Array type light-receiving device and hyperspectral spectrometer including array type light-receiving device

1. Field of the Invention

The present invention relates to an array type light-receiving device and a hyperspectral spectrometer including the array type light-receiving device.

2. Description of the Related Art

Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2013-93385) discloses light-receiving devices and related techniques. The light-receiving device described in Patent Literature 1 has a plurality of pixels disposed on a semiconductor substrate. Each of the pixels of the light-receiving device includes a light-receiving layer for receiving light, a p-n junction disposed in the light-receiving layer, and a mesa structure defined by grooves. The plurality of pixels is spaced apart from each other by the grooves disposed around the mesa structures. An impurity wall layer is disposed on a wall surface of the mesa structure so as to prevent the p-n junction from being exposed at the wall surface of the mesa structure. Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 2013-201219) discloses light-receiving devices and related techniques. The light-receiving device described in Patent Literature 2 has a plurality of pixels disposed on a semiconductor substrate. Each of the pixels includes a mesa structure defined by a groove. The mesa structure includes a light-receiving layer disposed in a stacked semiconductor layer, and a p-n junction located at an interface between the light-receiving layer and a p-type semiconductor layer disposed on the light-receiving layer. The plurality of pixels is separated from each other by the grooves disposed between the mesa structures. The groove is extended from a surface of the stacked semiconductor layer toward the semiconductor substrate through the p-n junction. The sidewall of the mesa structure is tapered such that the sectional area of the light-receiving layer is decreased toward the p-n junction. The semiconductor layer disposed on the light-receiving layer has an overhang portion that surrounds the p-n junction. The overhang portion of the semiconductor layer is overhung toward the grooves defining the mesa structure. Non-Patent Literature 1 (“MOVPE grown InGaAs/GaAsSb Type II Quantum Well Photodiode for SWIR Focal Plane Array”, H. Inada, H. Mori, Y. Nagai, Y. Iguchi, T. Saitoh, K. Fujii, T. Ishizuka, K. Akita, Proceeding of SPIE, vol. 8012 801220 (2011)) discloses a technique related to photodiodes having a type-II InGaAs/GaAsSb quantum well structure. Non-Patent Literature 1 describes a pixel size with a pixel pitch of 30 μm and a diameter of 15 μm.

A hyperspectral camera includes a two-dimensional array sensor that includes a plurality of pixels arranged in a lateral direction and a longitudinal direction. From the pixels arranged in the lateral direction, spatial information (image information) is obtained. In addition, from the pixels arranged in the longitudinal direction, wavelength information is obtained. By using the hyperspectral camera, the optical spectrum for each of the pixels arranged in the lateral direction for obtaining the spatial information (image information) is simultaneously obtained. For example, in the two-dimensional array sensor having 320×256 pixels, the 320 pixels arranged in the lateral direction provide spatial information. The 256 pixels arranged in the longitudinal direction provide wavelength information. In order to obtain the wavelength information, light that has been reflected from or passed through an object to be measured is spectrally diffracted by a spectroscope such as a prism. The light components diffracted spectrally are then incident on the 256 pixels of the array sensor arranged in the longitudinal direction so as to be converted into electrical signals (photocurrent). Where necessary, the object to be measured is irradiated with light by using a halogen lamp as a light source, especially in infrared hyperspectral systems. The electrical signals output from the array sensor are accumulated in capacitors in a read-out IC for a predetermined time (for example, 1 msec) and are thereafter read out to the outside. Usually, the array sensor has a responsivity having a wavelength dependence related to the semiconductor material constituting a light-receiving layer included in the pixels. When the light-receiving layer in the pixels is made of InGaAs, for example, the array sensor has a peak of responsivity at a wavelength of 1620 nm. Therefore, the photocurrent output from the pixel received a light component having a wavelength of 1620 nm is larger than the photocurrents output from the pixels received light components having wavelengths other than the wavelength of 1620 nm even when the light components have the same optical intensity. Capacitors in a read-out IC can store a limited amount of charges. The conditions (incident light intensity and accumulation time) to fully charge capacitors in a read-out IC are different in each of the capacitors according to the pixels connected to the capacitors. Specifically, when the light-receiving layer in the pixels is made of InGaAs, the capacitor connected to the pixel that receives light with a wavelength near 1620 nm is fully charged with a smaller optical intensity of the incident light and/or in a smaller accumulation time as compared with the capacitor connected to a pixel that receives light having a wavelength (a wavelength of below 1000 nm or above 1620 nm). When the conditions of the incident light intensity and the accumulation time of the capacitor are adjusted so that the capacitor connected to a pixel receiving a light having a wavelength at which the pixel has a smaller responsivity has an optimum amount of charges, the capacitor connected to a pixel receiving a light having a wavelength near 1620 nm at which the pixel has a larger responsivity is oversaturated. In the reverse case, the capacitor connected to a pixel receiving a light having a wavelength at which the pixel has a smaller responsivity is charged insufficiently and consequently the S/N ratio (the signal to noise ratio) of the pixel is decreased as compared with the capacitor connected to a pixel receiving a light having a wavelength near 1620 nm at which the pixel has a larger responsivity. In order to improve the S/N ratio of the pixel in the array sensor, it is desirable that conditions allow charges to be accumulated until immediately before the capacitors are saturated. However, the wavelength dependency of the responsivity of the pixel in the array sensor causes significant variations in the amounts of charges accumulated in the capacitors depending on wavelengths. Consequently, the S/N ratios are variable depending on wavelengths.

An array type light-receiving device according to an aspect of the present invention includes a plurality of pixels two-dimensionally arranged in a first direction and a second direction perpendicular to the first direction, each of the pixels including a light-receiving layer having a responsivity to a wavelength of light. The pixels arranged in the second direction constitute a plurality of pixel lines extending in the second direction, the plurality of pixel lines being arranged in the first direction to form an array. The pixels in each of the pixel lines have different pixel areas from each other. In addition, the pixel area of each of the pixels included in at least one of the pixel lines is determined in accordance with the responsivity to a wavelength of light received by each of the pixels.

FIG. 1 is a view illustrating an outside configuration of a hyperspectral spectrometer according to an embodiment.

FIG. 2 is a view illustrating an inside configuration of a hyperspectral spectrometer according to an embodiment.

FIG. 3 is a view illustrating a pixel array of an array type light-receiving device according to an embodiment.

FIG. 4 is a diagram illustrating spectral sensitivity characteristics of pixels having InGaAs light-receiving layers.

FIG. 5 is a view illustrating an arrangement of pixels and pixel areas for InGaAs light-receiving layers.

FIGS. 6A and 6B are views illustrating inside configurations of mesa-type photodetectors having mesa structures corresponding to pixels.

FIGS. 7A and 7B are views illustrating processes for manufacturing mesa-type photodetectors having mesa structures corresponding to pixels.

FIGS. 8A and 8B are views illustrating inside configurations of planar-type photodetectors having impurity diffusion regions corresponding to pixels.

FIGS. 9A and 9B are views illustrating processes for manufacturing planar-type photodetectors having impurity diffusion regions corresponding to pixels.

First, embodiments of the present invention will be listed and described. An array type light-receiving device according to an aspect of the present invention includes a plurality of pixels two-dimensionally arranged in a first direction and a second direction perpendicular to the first direction, each of the pixels including a light-receiving layer having a responsivity to a wavelength of light. The pixels arranged in the second direction constitute a plurality of pixel lines extending in the second direction, the plurality of pixel lines being arranged in the first direction to form an array. The pixels in each of the pixel lines have different pixel areas from each other. In addition, the pixel area of each of the pixels included in at least one of the pixel lines is determined in accordance with the responsivity to a wavelength of light received by each of the pixels.

In the array type light-receiving device according to one aspect of the invention, preferably, the pixels included in each of the pixel lines include a first pixel configured to receive light with a wavelength at which the pixel has a lowest responsivity in the responsivities to the wavelengths of incident light, and a second pixel other than the first pixel. The first pixel has the largest pixel area of the pixels included in the pixel line. The second pixel has a pixel area determined by the relational expression:

A β =E/R β ,

where A β represents the pixel area of the second pixel, E represents product of the responsivity of the first pixel at the wavelength of light received by the first pixel multiplied by the pixel area of the first pixel, and R β represents the responsivity of the second pixel at the wavelength of light received by the second pixel.

In the array type light-receiving device, the pixel area of each of the pixels included in at least one of the pixel lines is determined in accordance with the responsivity to the wavelength of light received by each of the pixels. Specifically, the pixel areas of the pixels are determined so that the product of the responsivity to the wavelength of light received by each of the pixels multiplied by the pixel area is constant. As a result, the amounts of light received by the pixels are controlled by changing the pixel areas of the pixels in accordance with the responsivities to wavelengths of light received by the pixels. Accordingly, photocurrents (charges) output from the pixels are uniform in receiving light components with the same intensity even when light components received by the pixels have different wavelengths. The difference in photocurrents (charges) output from the pixels due to the spectral sensitivity characteristics depending on the wavelengths of light is reduced. Accordingly, the S/N ratios of the pixels in the array type light-receiving device are improved.

In the array type light-receiving device according to one aspect of the invention, preferably, the plurality of pixels included in each of the pixel lines are arranged so as to receive corresponding light components having different wavelengths, the light components being separated along the second direction depending on the wavelengths. In the array type light-receiving device, the pixels included in each of the pixel lines receive corresponding light components having predetermined wavelengths. The pixel areas of the pixels are determined in accordance with the responsivities to the predetermined wavelengths of light components.

In the array type light-receiving device according to one aspect of the invention, the pixels arranged in the first direction may constitute a plurality of pixel rows extending in the first direction. The pixel areas of the pixels in each of the pixel rows may be approximately equal to each other.

Preferably, the array type light-receiving device according to one aspect of the invention further includes a plurality of mesas corresponding to the pixels, each of the mesas including the light-receiving layer, a passivation film disposed on a top surface and a side surface of the mesa, the passivation film including an opening on the top surface of the mesa, and an electrode disposed in the opening in contact with the top surface of the mesa.

Preferably, the array type light-receiving device according to one aspect of the invention further includes a plurality of impurity diffusion regions corresponding to the pixels, each of the impurity diffusion regions extending from a top surface of the pixel toward the light-receiving layer, a mask disposed on the top surface of the pixel, the mask having an opening on the impurity diffusion region, and an electrode disposed in the opening in contact with a top surface of the impurity diffusion region.

In the array type light-receiving device according to one aspect of the invention, the light-receiving layer may include an InGaAs layer. In addition, the light-receiving layer may have a multi quantum well structure including InGaAs layers and GaAsSb layers stacked alternately.

A hyperspectral spectrometer according to another aspect of the present invention includes an array type light-receiving device and a spectroscope configured to disperse an incident light spectrally into a plurality of light components having different wavelengths, the spectroscope outputting a dispersed light to the array type light-receiving device. The array type light-receiving device includes a plurality of pixels two-dimensionally arranged in a first direction and a second direction perpendicular to the first direction, each of the pixels including a light-receiving layer having a responsivity to a wavelength of light. The pixels arranged in the second direction constitute a plurality of pixel lines extending in the second direction, the plurality of pixel lines being arranged in the first direction to form an array. The light components of the dispersed light are separated along the second direction depending on the wavelengths. Each of the pixels in the pixel line is configured to receive at least one of the light components. In addition, the pixels in each of the pixel line have different pixel areas, each of which is determined in accordance with the responsivity to the wavelength of the light component received by each of the pixels.

Specific examples of the array type light-receiving devices according to embodiments of the present invention will be described below with reference to the drawings. However, the scope of the invention is defined by the appended claims and is not limited to such examples. It is intended that the scope of the invention covers all modifications that are within the spirit and scope equivalent to the claims.

FIG. 1 is a view illustrating a principal configuration of a hyperspectral spectrometer 1 . The hyperspectral spectrometer 1 includes a photodetector 2 , a spectroscopic device 3 and a cabinet 4 . The spectroscopic device 3 includes a lens 31 and a spectroscope 32 . The lens 31 is positioned to face a belt conveyer 5 . The spectroscope 32 is disposed on the lens 31 . The cabinet 4 is disposed on the spectroscope 32 . The photodetector 2 is disposed in the cabinet 4 and is positioned to face the spectroscopic device 3 . The spectroscopic device 3 receives light P 1 reflected from or passed through an object Ob 1 placed on the belt conveyer 5 . The light P 1 includes a plurality of light components having different wavelengths. When the light P 1 is incident on the spectroscopic device 3 , the spectroscopic device 3 spectrally disperses the light P 1 along a direction D 2 (the second direction) according to wavelengths, and outputs the dispersed light as light P 2 to the photodetector 2 . The light components of the dispersed light are separated along the direction D 2 (the second direction) depending on the wavelengths. The light P 1 and the light P 2 extend in a direction D 1 (the first direction) in accordance with the width of the object Ob 1 . The direction D 1 is perpendicular to the direction D 2 . A direction D 3 is perpendicular to the direction D 1 and the direction D 2 .

FIG. 2 is a schematic view illustrating a configuration of the hyperspectral spectrometer 1 as seen from a plane along line I-I in FIG. 1 . The photodetector 2 includes a read-out circuit board 21 and an array type light-receiving device 22 . The array type light-receiving device 22 has a surface S 1 and a surface S 2 opposite to the surface S 1 . The surface S 1 and the surface S 2 of the array type light-receiving device 22 extend along the direction D 1 and the direction D 2 . The surface S 1 is positioned to face the spectroscopic device 3 . In the embodiment, the surface S 1 of the array type light-receiving device 22 serves as a light incident surface on which light is incident. The read-out circuit board 21 is electrically connected to electrodes of the array type light-receiving device 22 disposed on the surface S 2 . The array type light-receiving device 22 includes a plurality of pixels K α×β . On the surface S 2 of the array type light-receiving device 22 , the plurality of pixels K α×β is two-dimensionally arranged to form a pixel array. The light P 1 coming from the object Ob 1 is dispersed by the spectroscopic device 3 in the direction D 2 and the dispersed light P 2 is incident on the plurality of pixels K α×β through the surface S 1 of the array type light-receiving device 22 .

The arrangement of N 1 ×N 2 pixels K α×β that constitute a pixel array KA of the array type light-receiving device 22 will be described with reference to FIG. 3 . The N 1 ×N 2 pixels K α×β are composed of the same material. Accordingly, the plurality of pixels K α×β constituting the pixel array KA has identical spectral sensitivity characteristics. FIG. 4 illustrates an example of the spectral sensitivity characteristics of the pixels included in the array type light-receiving device 22 . The spectral sensitivity characteristics indicate the responsivity (unit: A/W) according to the wavelength of incident light, namely, the wavelength dependency of responsivity. As shown in FIG. 4 , each of the pixels K α×β has spectral sensitivity characteristics depending on the wavelengths of the incident light. The responsivity of each of the pixels K α×β is varied according to the wavelengths of the incident light.

N 1 and N 2 are both integers of 2 or greater. For example, N 1 is 320 and N 2 is 256. The N 1 ×N 2 pixels K α×β are two-dimensionally arranged along the direction D 1 and direction D 2 on the surface S 2 of the array type light-receiving device 22 . The positions of the pixels K α×β in the direction D 1 correspond to the positions on a line of the object Ob 1 at which light P 1 is reflected from or passed through the object Ob 1 . The positions of the pixels K α×β in the direction D 2 correspond to the wavelengths of the light P 2 dispersed by the spectroscopic device 3 .

N 1 indicates the number of pixels K α×β in the direction D 1 . N 2 indicates the number of pixels K α×β in the direction D 2 . The character α indicates the position of the pixel in the array of the pixels K α×β in the direction D 1 , specifically, is any of the integers of 1 to N 1 . The character β indicates the position of the pixel in the array of the pixels K α×β in the direction D 2 , specifically, is any of the integers of 1 to N 2 . The N 1 pixels K α×β arranged in the direction D 1 have constant pitches L 1 . The N 2 pixels K α×β arranged in the direction D 2 have constant pitches L 2 .

The number of the plurality of pixels K α×β arranged in the direction D 1 (the line of pixels having a constant β) is N 1 . Specifically, the pixels K α×β include a pixel K 1×β , a pixel K 2×β , . . . and a pixel K N1×β (β is constant) arranged sequentially in the direction D 1 . The pixels K α×β (β is constant) arranged in the direction D 1 constitute a plurality of pixel rows extending in the direction D 1 . The pixel K 1×β , the pixel K 2×β , . . . and the pixel K N1×β (β is constant) have identical shapes such as squares or circles as seen in the direction D 3 that is perpendicular to the direction D 1 and the direction D 2 , and also have approximately equal pixel areas as seen in the direction D 3 . Of the light P 2 entering the array type light-receiving device 22 , a light component having a predetermined wavelength is incident on the pixel K 1×β , the pixel K 2×β , . . . and the pixel K N1×β (β is constant).

On the other hand, the number of the plurality of pixels K α×β arranged in the direction D 2 (the line of pixels having a constant α) is N 2 . Specifically, the pixels K α×β include a pixel K α×1 , a pixel K α×2 , . . . and a pixel K α×N2 (α is constant) arranged sequentially in the direction D 2 . The pixels K α×β (α is constant) arranged in the direction D 2 constitute a plurality of pixel lines extending in the direction D 2 . The pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant) have identical shapes such as squares or circles as seen in the direction D 3 . The pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant) have different pixel areas from each other. The respective pixel areas (areas as seen in the direction D 3 ) of the pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant) are determined in accordance with the wavelengths of light incident on the respective pixels.

The method for determining the respective pixel areas of a pixel K α×1 , a pixel K α×2 , . . . and a pixel K α×N2 (α is constant) will be described below. It is provided that the pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant) each have a responsivity R β (β is an integer of 1 to N 2 ) and a pixel area A β (β is an integer of 1 to N 2 ) as seen in the direction D 3 in accordance with the wavelengths of light incident on the respective pixels. Specifically, the light P 2 dispersed by the spectroscopic device 3 includes a plurality of light components having a wavelength λ 1 , a wavelength λ 2 , . . . and a wavelength λN 2 . In the line of the pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant), a light component having a wavelength λβ is incident on the pixel K α×β (α is constant and β is an integer of 1 to N 2 ). The magnitudes of the values of the wavelength λ 1 , the wavelength λ 2 , . . . and the wavelength λN 2 are λ 1 <λ 2 < . . . <λN 2 . Provided that the pixels K α×β (α is constant and β is an integer of 1 to N 2 ) show the lowest responsivity at a certain wavelength λi among the wavelength λ 1 the wavelength λ 2 , . . . and the wavelength λN 2 , this lowest responsivity R i of the responsivities R β is exhibited by a pixel in which β is i, namely, a pixel K α×i . In other words, the pixel K α×i is least responsive to the wavelength of light incident thereon among the pixels in the same pixel line, namely, the pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant). The pixel area A i of this pixel K α×i is made to be largest of the pixel areas A β . In other words, the pixel K α=i is given the largest pixel area A i of all the pixels included in the line of the pixel K α×1 , the pixel K α×2 , . . . and the pixel K α×N2 (α is constant). The pixel area A i is multiplied by the responsivity R i to give a product E, and the pixel areas A β are determined using A β =E/R β . That is, specifically, the pixel areas A β of the pixels K α×β (β is not i) in the line of the pixel K α×1 the pixel K α×2 , . . . and the pixel K α×N2 except the pixel K α×i (α is constant) are the quotients of the product E divided by the responsivities R β of the pixels K α×β (β is not i). Here, the product E is defined as the product of the responsivity R i and the pixel area A i of the pixel K α×i . The responsivities R β of the pixels K α×β (β is not i) correspond to the wavelengths of light incident on the respective pixels K α×β (β is not i).

As described above, the pixel areas A β of the pixels K α×β are determined such that the product of the responsivity R β multiplied by the pixel area A β is constant (the product E). Consequently, the pixels K α×β are allowed to output uniform charges (or photocurrents) even when each of the pixels K α×β receives one of light components of the light P 2 having different wavelengths from each other. That is, an amount of light received by each of the pixels K α×β is adjusted by controlling the pixel area A β according to the responsivity R β of the pixels K α×β . As a result, the difference in charges (or photocurrents) output from the pixels K α×β is reduced. Accordingly, the signals of the wavelength information having uniform and large S/N ratios are obtained for the pixels K α×β (α is constant and β is an integer of 1 to N 2 ) in the array type light-receiving device 22 .

As mentioned above, FIG. 4 illustrates spectral sensitivity characteristics of pixels K α×β in an array type light-receiving device 22 . The spectral sensitivity characteristics illustrated in FIG. 4 show a measurement result for the pixel K α×β having a light-receiving layer made of InGaAs. In FIG. 4 , the horizontal axis indicates the wavelength (unit: nm) of incident light, and the vertical axis indicates the responsivity (unit: A/W) at the wavelength. As illustrated in FIG. 5 , the pixels periodically arranged in the direction D 1 such as the pixels K 1×1 , to K 4×1 have pitches L 1 , and the pixels periodically arranged in the direction D 2 such as the pixels K 1×1 to K 1×6 in have pitches L 2 . In the embodiment, the pitches L 1 are the same as the pitches L 2 and are about 30 μm.

The arrangement of pixels K α×β illustrated in FIG. 5 is applicable to array type light-receiving devices 22 illustrated in FIG. 6A (First Example) and FIG. 8A (Second Example). The array type light-receiving devices 22 illustrated in FIG. 6A and FIG. 8A have sensitivity for light having wavelengths in the range of 1000 to 1640 nm. The array type light-receiving devices 22 will be described assuming that N 1 is 320 and N 2 is 256. Light components having a wavelength 43 ( 13 is an integer of 1 to 256) are incident on the 256 pixels K α×β (α is constant) arranged in the direction D 2 , at wavelength intervals of 2.5 nm (=640 nm/256). For example, a light component of the light P 2 which has λ 1 of 1000 nm is incident on the pixel K α×1 ; a light component of the light P 2 which has λ 2 of 1002.5 nm is incident on the pixel K α×2 ; a light component of the light P 2 which has λ 3 of 1005 nm is incident on the pixel K α×3 ; a light component of the light P 2 which has λ 4 of 1007.5 nm is incident on the pixel K α×4 ; a light component of the light P 2 which has λ 5 of 1010 nm is incident on the pixel K α×5 ; and a light component of the light P 2 which has λ 6 of 1012.5 nm is incident on the pixel K α×6 .

Referring to the spectral sensitivity characteristics illustrated in FIG. 4 , the responsivity of the 256 pixels K α×β (a is constant) arranged in the direction D 2 is lowest when β is 1, namely, the pixel K α×1 . The pixel K α×1 receives light having a wavelength λ 1 of 1000 nm. Referring to FIG. 4 , it is shown that the responsivity in the wavelength range of 1000 to 1640 nm is lowest at 1000 nm. Given that the pixels are squares and L 1 =L 2 =30 μm, the pixel area A 1 of this pixel K α×1 is the largest area available, namely, 26 μm×26 μm. The responsivity R 1 of the pixel K α×1 is about 0.7 [A/W]. That is, in array type light-receiving devices 22 including InGaAs light-receiving layers as will be described with reference to FIG. 6A (First Example) and FIG. 8A (Second Example), the product E (the product of the responsivity R 1 multiplied by the pixel area A 1 of the pixel K α×1 ) is approximately 26×26×0.7. The pixel areas A β of the pixels K α×β (α is constant) are determined using this product E and the responsivities R β corresponding to the wavelengths of light incident on the respective pixels K α×β .

First Example

Configurations of the photodetectors 2 will be described with reference to FIG. 6A and FIG. 6B . FIG. 6A schematically illustrates an inside configuration of the photodetector 2 as seen along a plane extending perpendicularly to the direction D 1 and the direction D 2 . FIG. 6B illustrates Modified Example 1 of the configuration illustrated in FIG. 6A . The photodetector 2 includes a read-out circuit board 21 , an array type light-receiving device 22 and bumps 23 . The read-out circuit board 21 and the array type light-receiving device 22 are electrically connected to each other through the bumps 23 . For example, the bumps 23 are composed of indium (In). The read-out circuit board 21 includes a substrate 211 and a plurality of electrodes 212 . The electrodes 212 are connected to the bumps 23 and are connected to p-side electrodes 22 f of the array type light-receiving device 22 through the bumps 23 . The array type light-receiving device 22 includes a substrate 22 a , a stacked semiconductor layer disposed on a principal surface of the substrate 22 a , a passivation film 22 e , the p-side electrode 22 f , an n-side electrode 22 g and a wiring electrode 22 h . The stacked semiconductor layer includes a buffer layer 22 b , a light-receiving layer 22 c and a capping layer 22 d . The array type light-receiving device 22 includes a plurality of mesas M.

The plurality of mesas M corresponds to the plurality of pixels K α×β . The pixel areas of the plurality of pixels K α×β are defined by the mesas M. Specifically, the pixel areas of the plurality of pixels K α×β correspond to areas of the mesas M as seen in the direction D 3 that is the direction perpendicular to the principal surface of the substrate 22 a . The buffer layer 22 b is disposed on the principal surface of the substrate 22 a . The light-receiving layer 22 c is disposed on the buffer layer 22 b . The capping layer 22 d is disposed on the light-receiving layer 22 c . The mesas M are disposed on the substrate 22 a . The mesa M includes the buffer layer 22 b , the light-receiving layer 22 c and the capping layer 22 d . A region E 1 shown in FIG. 6A includes the mesa M. The top surface and side surface of the mesa M are covered by the passivation film 22 e . The passivation film 22 e has an opening on the top surface of the capping layer 22 d . The p-side electrode 22 f is disposed in the opening of the passivation film 22 e . The p-side electrode 22 f is in contact with the capping layer 22 d through the opening of the passivation film 22 e . The wiring electrode 22 h and the n-side electrode 22 g are disposed at an outer periphery of the array type light-receiving device 22 . The wiring electrode 22 h is disposed on the passivation film 22 e and is in contact with the n-side electrode 22 g and the bump 23 . The n-side electrode 22 g is disposed on the substrate 22 a in contact with the buffer layer 22 b . The n-side electrode 22 g is connected to the electrode 212 of the read-out circuit board 21 through the wiring electrode 22 h and the bump 23 .

The buffer layer 22 b , the light-receiving layer 22 c and the capping layer 22 d are semiconductor layers sequentially disposed on the substrate 22 a . For example, the substrate 22 a is made of Fe-doped InP. The buffer layer 22 b is made of n-type InGaAs doped with Si. The thickness of the buffer layer 22 b is about 0.5 μm. The light-receiving layer 22 c is made of non-doped InGaAs. The thickness of the light-receiving layer 22 c is about 3 μm. The capping layer 22 d is made of p-type InGaAs doped with Zn. The thickness of the capping layer 22 d is about 1 μm. The p-side electrode 22 f includes Ti/Pt/Au. The n-side electrode 22 g includes Au/Ge/Ni. The passivation film 22 e is made of a dielectric material such as SiO 2 or SiN.

A process for manufacturing the photodetectors 2 will be schematically described with reference to FIG. 7A . First, a substrate 22 a _ 1 is provided. The substrate 22 a _ 1 corresponds to the substrate 22 a . The material of the substrate 22 a _ 1 is the same as the material of the substrate 22 a . On the substrate 22 a _ 1 , a semiconductor layer 22 b _ 1 , a semiconductor layer 22 c _ 1 and a semiconductor layer 22 d _ 1 are sequentially grown by an epitaxial growth method such as a metal-organic vapor phase epitaxy (MOVPE) method to form a stacked semiconductor layer. The semiconductor layer 22 b _ 1 corresponds to the buffer layer 22 b . The material of the semiconductor layer 22 b _ 1 is the same as the material of the buffer layer 22 b . The semiconductor layer 22 c _ 1 corresponds to the light-receiving layer 22 c . The material of the semiconductor layer 22 c _ 1 is the same as the material of the light-receiving layer 22 c . The semiconductor layer 22 d _ 1 corresponds to the capping layer 22 d . The material of the semiconductor layer 22 d _is the same as the material of the capping layer 22 d.

Next, the stacked semiconductor layer including the semiconductor layer 22 b _ 1 , the semiconductor layer 22 c _ 1 and the semiconductor layer 22 d _ 1 is etched by using a dry etching method. This etching results in the formation of mesas M corresponding to the pixels. A p-n junction is formed at an interface between the semiconductor layer 22 c _ 1 (light-receiving layer 22 c ) and the semiconductor layer 22 d _ 1 (capping layer 22 d ) in each of the mesas M. Further, a passivation film of SiO 2 (corresponding to the passivation film 22 e ) is formed on the surface of the mesas M. The passivation film covers the p-n junction exposed at a side surface of the mesa M to reduce a leak current. Next, openings are formed in the passivation film to reach the surface of the semiconductor layer 22 d _ 1 , and p-side electrodes 22 f are formed in the openings of the passivation film. Further, n-side electrodes 22 g are formed on the surface of the semiconductor layer 22 b _ 1 at locations corresponding to outer peripheries of array type light-receiving devices 22 . Through these steps, a wafer is formed which includes array type light-receiving devices 22 illustrated in FIG. 6A . Thereafter, the wafer is divided into a plurality of chips corresponding to the array type light-receiving devices 22 illustrated in FIG. 6A . On each of the chips, a plurality of bumps 23 is formed. This chip and a read-out circuit board 21 are bonded to each other through the plurality of bumps 23 by flip chip bonding. Through these steps, the photodetectors 2 of First Example are produced.

Another configuration of the mesas M illustrated in FIG. 6B will be described (Modified Example 1 of First Example). The mesas M may include a light-receiving layer 22 i , a semiconductor layer 22 j and a capping layer 22 k in place of the light-receiving layer 22 c and the capping layer 22 d illustrated in FIG. 6A . The light-receiving layer 22 i is disposed on the buffer layer 22 b . The semiconductor layer 22 j is disposed on the light-receiving layer 22 i . The capping layer 22 k is disposed on the semiconductor layer 22 j . The light-receiving layer 22 i , the semiconductor layer 22 j and the capping layer 22 k are semiconductor layers disposed sequentially on the substrate 22 a . The light-receiving layer 22 i has a type-II multi quantum well (MQW) structure. For example, the MQW structure is composed of non-doped InGaAs layers (thickness 5 nm) and non-doped GaAsSb layers (thickness 5 nm) that are staked alternately. The MQW structure includes 250 pairs of the InGaAs layers and the GaAsSb layers. The thickness of the light-receiving layer 22 i is about 2.5 μm. The semiconductor layer 22 j is made of non-doped InGaAs. The thickness of the semiconductor layer 22 j is about 0.1 μm. The capping layer 22 k is made of p-type InGaAs doped with Zn, for example. The thickness of the capping layer 22 k is about 0.6 μm.

A process for manufacturing the photodetectors 2 of Modified Example 1 will be schematically described with reference to FIG. 7B . First, a substrate 22 a _ 1 is provided. The substrate 22 a _ 1 corresponds to the substrate 22 a . The material of the substrate 22 a _ 1 is the same as the material of the substrate 22 a . On the substrate 22 a _ 1 , a semiconductor layer 22 b _ 1 , a semiconductor layer 22 i _ 1 , a semiconductor layer 22 j _ 1 and a semiconductor layer 22 k _ 1 are sequentially grown by an epitaxial growth method such as a MOVPE method to form a stacked semiconductor layer. The semiconductor layer 22 i _ 1 corresponds to the light-receiving layer 22 i . The material of the semiconductor layer 22 i _ 1 is the same as the material of the light-receiving layer 22 i . The semiconductor layer 22 j _ 1 corresponds to the semiconductor layer 22 j . The material of the semiconductor layer 22 j _ 1 is the same as the material of the semiconductor layer 22 j . The semiconductor layer 22 k _ 1 corresponds to the capping layer 22 k . The material of the semiconductor layer 22 k _ 1 is the same as the material of the capping layer 22 k.

Next, the stacked semiconductor layer including the semiconductor layer 22 b _ 1 , the semiconductor layer 22 i _ 1 , the semiconductor layer 22 j _ 1 and the semiconductor layer 22 k _ 1 is etched by using a dry etching method to form mesas M corresponding to the pixels. A p-n junction is formed at an interface between the semiconductor layer 22 i _ 1 (light-receiving layer 22 i ) and the semiconductor layer 22 j _ 1 (semiconductor layer 22 j ) in each of the mesas M. Further, a passivation film of SiO 2 (corresponding to the passivation film 22 e ) is formed on the surface of the mesas M. The passivation film covers the p-n junction exposed at a side surface of the mesa M to reduce a leak current. Next, openings are formed in the passivation film to reach the surface of the semiconductor layer 22 k _ 1 , and p-side electrodes 22 f are formed in the openings of the passivation film. Further, n-side electrodes 22 g are formed on the surface of the semiconductor layer 22 b _ 1 at locations corresponding to outer peripheries of array type light-receiving devices 22 of Modified Example 1. Through these steps, a wafer is formed which includes array type light-receiving devices 22 of Modified Example 1. Thereafter, the wafer is divided into a plurality of chips corresponding to the array type light-receiving devices 22 of Modified Example 1. On each of the chips, a plurality of bumps 23 is formed. This chip and a read-out circuit board 21 are bonded to each other through the plurality of bumps 23 by flip chip bonding. Through these steps, the photodetectors 2 of Modified Example 1 are produced.

Second Example

Configurations of photodetectors 2 _ 1 will be described with reference to FIG. 8A and FIG. 8B . The configurations of the photodetectors 2 _ 1 correspond to the configurations of the photodetectors 2 of First Example except that the array type light-receiving device 22 of First Example is replaced by an array type light-receiving device 22 _ 1 of Second Example. The configurations of hyperspectral spectrometers 1 _ 1 correspond to the configurations of the hyperspectral spectrometers 1 of First Example except that the photodetector 2 of First Example is replaced by the photodetector 2 _ 1 of Second Example. Referring to FIGS. 1 to 3 , the hyperspectral spectrometer 1 may be replaced by the hyperspectral spectrometer 1 _ 1 of Second Example, the photodetector 2 may be replaced by the photodetector 2 _ 1 of Second Example, and the array type light-receiving device 22 may be replaced by the array type light-receiving device 22 _ 1 of Second Example.

FIG. 8A schematically illustrates an inside configuration of the photodetector 2 _ 1 as seen along a plane extending perpendicularly to the direction D 1 and the direction D 2 . FIG. 8B illustrates Modified Example 2 of the configuration illustrated in FIG. 8A . The photodetector 2 _ 1 includes a read-out circuit board 21 , an array type light-receiving device 22 _ 1 and bumps 23 . The read-out circuit board 21 and the array type light-receiving device 22 _ 1 are electrically connected to each other through the bumps 23 . For example, the bumps 23 are composed of indium (In). The read-out circuit board 21 includes a substrate 211 and a plurality of electrodes 212 . The electrodes 212 of the read-out circuit board 21 are connected to the bumps 23 . The electrodes 212 are also connected to p-side electrodes 22 t of the array type light-receiving device 22 _ 1 through the bumps 23 . The array type light-receiving device 22 _ 1 includes a substrate 22 m , a stacked semiconductor layer disposed on a principal surface of the substrate 22 m , a mask 22 s , the p-side electrode 22 t , an n-side electrode 22 u and a wiring electrode 22 v . The stacked semiconductor layer includes a buffer layer 22 n , a light-receiving layer 22 p , a capping layer 22 q and an impurity diffusion region 22 r . The array type light-receiving device 22 _ 1 includes a plurality of impurity diffusion regions 22 r.

The plurality of impurity diffusion regions 22 r corresponds to the plurality of pixels K α×β . The pixel areas of the plurality of pixels K α×β , are defined by the impurity diffusion regions 22 r . Specifically, the pixel areas of the plurality of pixels K α×β correspond to areas of the impurity diffusion regions 22 r as seen in the direction D 3 that is the direction perpendicular to the principal surface of the substrate 22 m . The buffer layer 22 n is disposed on the principal surface of the substrate 22 m . The light-receiving layer 22 p is disposed on the buffer layer 22 n . The capping layer 22 q is disposed on the light-receiving layer 22 p . The impurity diffusion regions 22 r are disposed on the surface (the surface S 2 ) of the capping layer 22 q . The impurity diffusion regions 22 r extend from the surface of the capping layer 22 q toward the light-receiving layer 22 p . A region E 2 shown in FIG. 8A includes the impurity diffusion region 22 r . The top surface of the capping layer 22 q is covered by the mask 22 s . The mask 22 s has an opening on the top surface of the capping layer 22 q (the top surface of the impurity diffusion region 22 r ). The p-side electrode 22 t is disposed in the opening of the mask 22 s . The p-side electrode 22 t is in contact with the capping layer 22 q (the impurity diffusion region 22 r ) through the opening of the mask 22 s . The wiring electrode 22 v and the n-side electrode 22 u are disposed at an outer periphery of the array type light-receiving device 22 _ 1 . The wiring electrode 22 v is disposed on the mask 22 s and is in contact with the n-side electrode 22 u and the bump 23 . The n-side electrode 22 u is disposed on the substrate 22 m in contact with the buffer layer 22 n . The n-side electrode 22 u is connected to the electrode 212 of the read-out circuit board 21 through the wiring electrode 22 v and the bump 23 .

The buffer layer 22 n , the light-receiving layer 22 p and the capping layer 22 q are semiconductor layers sequentially disposed on the substrate 22 m . For example, the substrate 22 m is made of Si-doped InP. The buffer layer 22 n is made of n-type InGaAs doped with Si. The thickness of the buffer layer 22 n is about 0.5 m. The light-receiving layer 22 p is made of non-doped InGaAs. The thickness of the light-receiving layer 22 p is about 3 μm. The capping layer 22 q is made of non-doped InP. The thickness of the capping layer 22 q is about 1.5 μm. The p-side electrode 22 t includes Au/Zn. The n-side electrode 22 u includes Au/Ge/Ni. The mask 22 s is made of a SiN film, for example.

A process for manufacturing the photodetectors 2 _ 1 will be schematically described with reference to FIG. 9A . First, a substrate 22 m _ 1 is provided. The substrate 22 m _ 1 corresponds to the substrate 22 m . The material of the substrate 22 m _ 1 is the same as the material of the substrate 22 m . On the substrate 22 m _ 1 , a semiconductor layer 22 n _ 1 , a semiconductor layer 22 p _ 1 and a semiconductor layer 22 q _ 1 are sequentially grown by an epitaxial growth method such as a MOVPE method to form a stacked semiconductor layer. The semiconductor layer 22 n _ 1 corresponds to the buffer layer 22 n . The material of the semiconductor layer 22 n _ 1 is the same as the material of the buffer layer 22 n . The semiconductor layer 22 p _ 1 corresponds to the light-receiving layer 22 p . The material of the semiconductor layer 22 p _ 1 is the same as the material of the light-receiving layer 22 p . The semiconductor layer 22 q _ 1 corresponds to the capping layer 22 q . The material of the semiconductor layer 22 q _ 1 is the same as the material of the capping layer 22 q.

Next, a mask composed of a SiN film (corresponding to the mask 22 s ) is provided on the surface of the semiconductor layer 22 q _ 1 . The mask has a pattern having openings through which p-type impurity such as zinc (Zn) is selectively diffused. Through the mask, zinc (Zn) is diffused from the surface of the semiconductor layer 22 q _ 1 (capping layer 22 q ) toward the semiconductor layer 22 p _ 1 (light-receiving layer 22 p ). This diffusion results in the formation of impurity diffusion regions 22 r corresponding to the pixels. A p-n junction is formed at a diffusion front of Zn in the impurity diffusion regions 22 r . For example, the p-n junction is formed at an interface between the semiconductor layer 22 q _ 1 and the semiconductor layer 22 p _ 1 in each of the pixels. The p-n junction may be formed at an upper portion of the semiconductor layer 22 p _ 1 . Next, p-side electrodes 22 t are formed in the openings of the mask in contact with the top surface of the impurity diffusion regions 22 r . In the embodiment, the mask on the surface of the semiconductor layer 22 q _ 1 that is used for diffusing zinc (Zn) is not removed and becomes the mask 22 s . Further, n-side electrodes 22 u are formed on the surface of the semiconductor layer 22 n _ 1 at locations corresponding to outer peripheries of array type light-receiving devices 22 _ 1 . Through these steps, a wafer is formed which includes array type light-receiving devices 22 _ 1 illustrated in FIG. 8A . Thereafter, the wafer is divided into a plurality of chips corresponding to the array type light-receiving devices 22 _ 1 illustrated in FIG. 8A . On each of the chips, a plurality of bumps 23 is formed. This chip and a read-out circuit board 21 are bonded to each other through the plurality of bumps 23 by flip chip bonding. Through these steps, the photodetectors 2 _ 1 of Second Example are produced.

Next, another configuration illustrated in FIG. 8B will be described (Modified Example 2 of Second Example). The array type light-receiving device 221 may include a light-receiving layer 22 w , a semiconductor layer 22 x and a capping layer 22 y in place of the light-receiving layer 22 p and the capping layer 22 q illustrated in FIG. 8A . The light-receiving layer 22 w is disposed on the buffer layer 22 n . The semiconductor layer 22 x is disposed on the light-receiving layer 22 w . The capping layer 22 y is disposed on the semiconductor layer 22 x . The buffer layer 22 n , the light-receiving layer 22 w , the semiconductor layer 22 x and the capping layer 22 y are semiconductor layers disposed sequentially on the substrate 22 m . The light-receiving layer 22 w has a type-II MQW structure. For example, the MQW structure is composed of non-doped InGaAs layers (thickness 5 nm) and non-doped GaAsSb layers (thickness 5 nm) that are stacked alternately. The MQW structure includes 250 pairs of the InGaAs layers and the GaAsSb layers. The thickness of the light-receiving layer 22 w is about 2.5 μm. The semiconductor layer 22 x is made of non-doped InGaAs. The thickness of the semiconductor layer 22 x is about 1 μm. The capping layer 22 y is made of non-doped or Si-doped InP to form a n-type InP layer. The thickness of the capping layer 22 y is about 0.8 μm. An impurity diffusion region 22 z is a Zn-diffused region and extends from the surface of the capping layer 22 y to the light-receiving layer 22 w.

A process for manufacturing the photodetectors 2 _ 1 of Modified Example 2 will be schematically described with reference to FIG. 9B . First, a substrate 22 m _ 1 is provided. The substrate 22 m _ 1 corresponds to the substrate 22 m . The material of the substrate 22 m _ 1 is the same as the material of the substrate 22 m . On the substrate 22 m _ 1 , a semiconductor layer 22 n _ 1 , a semiconductor layer 22 w _ 1 , a semiconductor layer 22 x _ 1 and a semiconductor layer 22 y _ 1 are sequentially grown by an epitaxial growth method such as a MOVPE method to form a stacked semiconductor layer. The semiconductor layer 22 w _ 1 corresponds to the light-receiving layer 22 w . The material of the semiconductor layer 22 w _ 1 is the same as the material of the light-receiving layer 22 w . The semiconductor layer 22 x _ 1 corresponds to the semiconductor layer 22 x . The material of the semiconductor layer 22 x _ 1 is the same as the material of the semiconductor layer 22 x . The semiconductor layer 22 y _ 1 corresponds to the capping layer 22 y . The material of the semiconductor layer 22 y _ 1 is the same as the material of the capping layer 22 y.

Next, a mask composed of a SiN film is formed on the surface of the semiconductor layer 22 y _ 1 . The mask has a pattern having openings through which p-type impurity such as zinc (Zn) is selectively diffused. Through the mask, zinc (Zn) is selectively diffused from the surface of the semiconductor layer 22 y _ 1 (capping layer 22 y ) toward the semiconductor layer 22 w _ 1 (light-receiving layer 22 w ) through the semiconductor layer 22 x _ 1 (semiconductor layer 22 x ). This selective diffusion results in the formation of impurity diffusion regions 22 z corresponding to the pixels. A p-n junction is formed at a diffusion front of Zn in the impurity diffusion regions 22 z . The concentration and diffusion depth of Zn impurity in the semiconductor layer 22 w _ 1 (light-receiving layer 22 w ) is controlled by adjusting the thickness of the semiconductor layer 22 x _ 1 . For example, the p-n junction is formed in the semiconductor layer 22 x _ 1 or at an interface between the semiconductor layer 22 x _ 1 and the semiconductor layer 22 w _ 1 . The p-n junction may be formed at an upper portion of the semiconductor layer 22 w _ 1 . Next, p-side electrodes 22 t are formed in the openings of the mask on the surface of the impurity diffusion regions 22 z while remaining the mask on the surface of the semiconductor layer 22 y _ 1 . The p-side electrodes 22 t are in contact with the top surface of the impurity diffusion regions 22 z . Further, n-side electrodes 22 u are formed on the surface of the semiconductor layer 22 n _ 1 at locations corresponding to outer peripheries of array type light-receiving devices 22 _ 1 of Modified Example 2. Through these steps, a wafer is formed which includes array type light-receiving devices 22 _ 1 of Modified Example 2. Thereafter, the wafer is divided into a plurality of chips corresponding to the array type light-receiving devices 22 _ 1 of Modified Example 2. On each of the chips, a plurality of bumps 23 is formed. This chip and a read-out circuit board 21 are bonded to each other through the plurality of bumps 23 by flip chip bonding. Through these steps, the photodetectors 2 _ 1 of Modified Example 2 are produced.

While preferred embodiments have been discussed above while illustrating the principle of the present invention, those skilled in the art will appreciate that various modifications may be made to the configurations and the details discussed above without departing from the principle of the invention. The scope of the invention is not limited to any specific configurations disclosed in the embodiments. Therefore, the features defined in the appended claims and all modifications and alterations which are within the spirit of the invention are claimed.