Group III intride semiconductor light emitting element

The present application is based on Japanese patent application No.2006-106805, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

This invention relates to a group III nitride semiconductor light emitting element and, in particular, to a group III nitride semiconductor light emitting element that uses as a light emitting layer an MQW (multiquantum well) structure with a well layer such as InGaN layer.

2. Description of the Related Art

In recent years, light emitting apparatuses using a semiconductor element (light emitting element) such as an LED (light emitting diode) and a LD (laser diode) are widely used as a light source since they are smaller, more excellent in power efficiency or longer in lifetime than light bulbs.

In such a semiconductor light emitting element, a blue/green light emitting diode and a violet semiconductor laser diode using an active layer (light emitting layer) with an In x Ga 1−x N MQW structure have been commercialized already.

A conventional group III nitride semiconductor light emitting element is known that plural well layers composing the light emitting layer are set to be different from each other in composition ratio of components to compose the well layers (e.g., JP-A-10-022525).

However, the conventional group III nitride semiconductor light emitting element has a problem that the well layers each have an emission wavelength different from each other to cause deterioration in color purity and reduction in emission intensity, since the screening effect is different between the well layers due to a difference in piezooptical effect level and in carrier concentration therebetween.

It is an object of the invention to provide a group III nitride semiconductor light emitting element that has well layers to-coincide in emission wavelength with each other to achieve excellent color purity and to enhance the emission intensity.

According to one embodiment of the invention, a group III nitride semiconductor light emitting element comprises:

a light emitting layer comprising a multiquantum well structure comprising a group III nitride semiconductor, wherein the light emitting layer comprises a plurality of well layers, and the plurality of well layers are formed to coincide in emission wavelength with each other.

In the above invention, the following modifications and changes can be made.

(i) The light emitting layer comprises a plurality of pair layers, each of the pair layers comprising a well layer and a barrier layer, the light emitting element further comprises a p-semiconductor layer, and the barrier layer is situated nearer the p-semiconductor layer in relation to the well layer.

(ii) The plurality of well layers comprises InGaN, and

the plurality of well layers are different from each other in composition ratio of the InGaN. The light emitting element further comprises an n-semiconductor layer and a p-semiconductor layer, and an In composition ratio of the InGaN decreases in a direction from the n-semiconductor layer to the p-semiconductor layer.

(iii) The plurality of well layers comprises InGaN and silicon (Si) doped as an impurity, and the plurality of well layers are different from each other in doping amount of the Si. The light emitting element further comprises an n-semiconductor layer and a p-semiconductor layer, and the Si doping amount increases in a direction from the n-semiconductor layer to the p-semiconductor layer.

(iv) The plurality of well layers comprises InGaN, and the plurality of well layers are different from each other in thickness. The light emitting element further comprises an n-semiconductor layer and a p-semiconductor layer, and the thickness decreases in a direction from the n-semiconductor layer to the p-semiconductor layer.

(v) The plurality of well layers comprises InGaN, and the plurality of well layers are different from each other in bandgap width. The light emitting element further comprises an n-semiconductor layer and a p-semiconductor layer, and a bandgap width of the plurality of well layers increases in a direction from the n-semiconductor layer to the p-semiconductor layer.

(vi) The light emitting element further comprises an n-semiconductor layer and a p-semiconductor layer, and the bandgap width increases in a direction from the n-semiconductor layer to the p-semiconductor layer.

The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:

FIG. 1A is a schematic cross sectional view showing a group III nitride semiconductor light emitting element in a first preferred embodiment according to the invention;

FIG. 1B is a schematic cross sectional view showing a light emitting layer of the light emitting element in FIG. 1A ;

FIG. 2A is a diagram showing an emission spectrum of light emitted from the group III nitride semiconductor light emitting element of the first embodiment;

FIG. 2B is a diagram showing an emission spectrum of light emitted from a conventional group III nitride semiconductor light emitting element;

FIG. 3 is a schematic cross sectional view showing a light emitting layer of a group III nitride semiconductor light emitting element in a second preferred embodiment according to the invention; and

FIG. 4 is a schematic cross sectional view showing a light emitting layer of a group III nitride semiconductor light emitting element in a second preferred embodiment according to the invention.

First Embodiment

FIG. 1A is a schematic cross sectional view showing a group III nitride semiconductor light emitting element in the first preferred embodiment according to the invention. FIG. 1B is a schematic cross sectional view showing a light emitting layer of the light emitting element in FIG. 1A .

As shown in FIG. 1A , the group III nitride semiconductor light emitting element 1 comprises a p-side electrode 18 and an n-side electrode 19 , and further comprises an AlN buffer layer 11 grown on a sapphire substrate under low-temperature growth conditions, an Si-doped n + -GaN layer 12 , an Si-doped n-AlGaN layer 13 , an MQW 14 with a multiquantum well structure formed of InGaN/GaN, an Mg-doped p-AlGaN layer 15 , an Mg-doped p + -GaN layer 16 , and a current spreading layer 17 as a conductive film, which are stacked sequentially. It functions as a blue LED element to emit, e.g., a bluish light with an emission wavelength of 460 nm to 463 nm.

The AlN buffer layer 11 is formed by supplying trimethylgallium (TMG) into a reactor in which the sapphire substrate 10 is placed under a growth temperature condition of 350° C. to 550° C. (preferably 400° C. to 550° C.) while using H 2 as a carrier gas.

The n + -GaN layer 12 and the p + -GaN layer 16 are formed by supplying NH 3 and trimethylgallium (TMG) into the reactor under a growth temperature condition of 1100° C. while using H 2 as a carrier gas. Monosilane as an Si source is used for a dopant to provide n-type conductivity with the n + -GaN layer 12 , and cyclopentadienyl magnesium (Cp 2 Mg) as an Mg source used for a dopant to provide p-type conductivity with the p + -GaN layer 16 .

The n-AlGaN layer 13 and the p-AlGaN layer 15 are formed by supplying NH 3 , TMG and trimethylaluminum (TMA) into the reactor under a temperature condition of 1100° C. SiH 4 as an Si source is used for a dopant to provide n-type conductivity with the n-AlGaN layer 13 , and cyclopentadienyl magnesium (Cp 2 Mg) as an Mg source used for a dopant to provide p-type conductivity with the p-AlGaN layer 15 .

As shown in FIG. 1B , the MQW 14 is formed with a light emitting layer comprising a first pair layer 21 to a fourth pair layer 24 , each being formed of a group III nitride semiconductor. A first well layer to a fourth well layer to compose the MQW 14 are each formed under growth conditions to coincide in emission wavelength with each other, as mentioned later. Si is doped as an impurity into the second well layer to the fourth well layer. The amount of the Si doped is set to increase gradually from the n-semiconductor layer side to the p-semiconductor layer side. The thickness of the first well layer to the fourth well layer is set to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The group III nitride semiconductor means at least group III-V nitride semiconductor represented by In x Ga 1−x N (where 0≦x≦1). In x (x: composition ratio) is set to have composition ratios to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The MQW 14 is formed by supplying NH 3 , TMG and trimethylindium (TMI) into the reactor under a growth temperature condition of 700° C. to 900° C. while using N 2 as a carrier gas.

The first pair layer 21 is composed of the first well layer 21 A and a first barrier layer 21 B, and formed on the n-AlGaN 13 . The first well layer 21 A is disposed on the n-semiconductor layer side in relation to the first barrier layer 21 B, and formed of an In 0.26 Ga 0.74 N layer with a thickness of about 38 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The first barrier layer 21 B is disposed on the p-semiconductor layer side in relation to the first well layer 21 A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer 22 is composed of a second well layer 22 A and a second barrier layer 22 B, and formed on the first pair layer 21 . The second well layer 22 A is disposed on the n-semiconductor layer side in relation to the second barrier layer 22 B, and formed of an In 0.23 Ga 0.77 N layer with a thickness of about 34 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The second well layer 22 A is doped with an impurity, silicon (Si) at a doping amount of about 2×10 −7 cm −3 . The second barrier, layer 22 B is disposed on the p-semiconductor layer side in relation to the second well layer 22 A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer 23 is composed of a third well layer 23 A and a third barrier layer 23 B, and formed on the second pair layer 22 . The third well layer 23 A is disposed on the n-semiconductor layer side in relation to the third barrier layer 23 B, and formed of an In 0.20 Ga 0.80 N layer with a thickness of about 30 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The third well layer 23 A is doped with an impurity, silicon (Si) at a doping amount of about 4×10 −7 cm −3 . The third barrier layer 23 B is disposed on the p-semiconductor layer side in relation to the third well layer 23 A, and formed of a GaN layer with a thickness of about 5 nm.

The fourth pair layer 24 is composed of a fourth well layer 24 A and a fourth barrier layer 24 B, and formed on the third pair layer 23 . The fourth well layer 24 A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer 24 B, and formed of an In 0.17 Ga 0.83 N layer with a thickness of about 26 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The fourth well layer 24 A is doped with an impurity, silicon (Si) at a doping amount of about 6×10 −7 cm −3 . The fourth barrier layer 24 B is disposed on the p-semiconductor layer side in relation to the fourth well layer 24 A, and formed of a GaN layer with a thickness of about 5 nm.

The In (=indium) composition ratio, thickness and Si doping concentration of the first well layer 21 A to the fourth well layer 24 A are as shown in Table 1.

The current spreading layer 17 is disposed on the p + -GaN layer 16 , and formed of a transparent electrode made of Indium tin oxide (ITO).

The p-side electrode 18 is formed on the surface of the current spreading layer 17 , and the n-side electrode 19 is formed on the surface of the n + -GaN layer 12 exposed by etching.

In applying a voltage from a power source to the group III nitride semiconductor light emitting element 1 thus structured, light emitted from the MQW 14 is observed where an emission spectrum with a sharp emission wavelength peak (emission wavelength: 460 nm to 463 nm) is confirmed. This is as shown in FIG. 2A where the vertical axis indicates emission intensity and the horizontal axis indicates wavelength. As shown in FIG. 2A , the emission spectrum observed has an FWHM (=full-width at half-maximum) of 20 nm.

In contrast, as shown in FIG. 2B , the emission spectrum of light emitted from a conventional MQW has an emission wavelength peak of 440 nm to 470 nm and an FWHM of 27 nm.

In addition, as shown in FIGS. 2A and 2B , the emission intensity of this embodiment can be enhanced to 1.3 relative to 1 in case of the conventional MQW.

The following effects can be obtained by the first embodiment as mentioned above.

Since the first well layer 21 to the fourth well layer 24 are each formed to coincide in emission wavelength with each other, excellent color purity can be achieved and the emission intensity can be enhanced.

Second Embodiment

FIG. 3 is a schematic cross sectional view showing a light emitting layer of a group III nitride semiconductor light emitting element in the second preferred embodiment according to the invention.

As shown in FIG. 3 , an MQW 30 of the group III nitride semiconductor light emitting element of the second embodiment is formed with the light emitting layer comprising a first pair layer 31 to a sixth pair layer 36 , each being formed of a group III nitride semiconductor. A first well layer to a sixth well layer to compose the MQW 30 are each formed under growth conditions to coincide in emission wavelength with each other, as mentioned later. Si is doped as an impurity into the second well layer to the sixth well layer. The amount of the Si doped is set to increase gradually from the n-semiconductor layer side to the p-semiconductor layer side. The thickness of the first well layer to the sixth well layer is set to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The group III nitride semiconductor means at least group III-V nitride semiconductor represented by In x Ga 1−x N (where 0≦x≦1). In x (x: composition ratio) is set to have composition ratios to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The MQW 30 is formed by supplying NH 3 , TMG and TMI into the reactor under a growth temperature condition of 700° C. to 900° C. while using N 2 as a carrier gas.

The first pair layer 31 is composed of the first well layer 31 A and a first barrier layer 31 B, and formed on the n-AlGaN 13 as shown in FIG. 1A . The first well layer 31 A is disposed on the n-semiconductor layer side in relation to the first barrier layer 31 B, and formed of an In 0.26 Ga 0.74 N layer with a thickness of about 39 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The first barrier layer 31 B is disposed on the p-semiconductor layer side in relation to the first well layer 31 A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer 32 is composed of a second well layer 32 A and a second barrier layer 32 B, and formed on the first pair layer 31 . The second well layer 32 A is disposed on the n-semiconductor layer side in relation to the second barrier layer 32 B, and formed of an In 0.24 Ga 0.76 N layer with a thickness of about 36 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The second well layer 32 A is doped with an impurity, silicon (Si) at a doping amount of about 1×10 −7 cm −3 . The second barrier layer 32 B is disposed on the p-semiconductor layer side in relation to the second well layer 32 A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer 33 is composed of a third well layer 33 A and a third barrier layer 33 B, and formed on the second pair layer 32 . The third well layer 33 A is disposed on the n-semiconductor layer side in relation to the third barrier layer 33 B, and formed of an In 0.22 Ga 0.78 N layer with a thickness of about 30 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The third well layer 33 A is doped with an impurity, silicon (Si) at a doping amount of about 2×10 −7 cm −3 . The third barrier layer 33 B is disposed on the p-semiconductor layer side in relation to the third well layer 33 A, and formed of a GaN layer with a thickness of about 5 nm.

A fourth pair layer 34 is composed of a fourth well layer 34 A and a fourth barrier layer 34 B, and formed on the third pair layer 33 . The fourth well layer 34 A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer 34 B, and formed of an In 0.20 Ga 0.80 N layer with a thickness of about 30 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The fourth well layer 34 A is doped with an impurity, silicon (Si) at a doping amount of about 3×10 −7 cm −3 . The fourth barrier layer 34 B is disposed on the p-semiconductor layer side in relation to the fourth well layer 34 A, and formed of a GaN layer with a thickness of about 5 nm.

A fifth pair layer 35 is composed of a fifth well layer 35 A and a fifth barrier layer 35 B, and formed on the fourth pair layer 34 . The fifth well layer 35 A is disposed on the n-semiconductor layer side in relation to the fifth barrier layer 35 B, and formed of an In 0.18 Ga 0.82 N layer with a thickness of about 27 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The fifth well layer 35 A is doped with an impurity, silicon (Si) at a doping amount of about 4×10 −7 cm −3 . The fifth barrier layer 35 B is disposed on the p-semiconductor layer side in relation to the fifth well layer 35 A, and formed of a GaN layer with a thickness of about 5 nm.

The sixth pair layer 36 is composed of a sixth well layer 36 A and a sixth barrier layer 36 B, and formed on the fifth pair layer 35 . The sixth well layer 36 A is disposed on the n-semiconductor layer side in relation to the sixth barrier layer 36 B, and formed of an In 0.16 Ga 0.84 N layer with a thickness of about 24 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The sixth well layer 36 A is doped with an impurity, silicon (Si) at a doping amount of about 5×10 −7 cm −3 . The sixth barrier layer 36 B is disposed on the p-semiconductor layer side in relation to the sixth well layer 36 A, and formed of a GaN layer with a thickness of about 5 nm.

The In (indium) composition ratio, thickness and Si doping concentration of the first well layer 31 A to the sixth well layer 36 A are as shown in Table 2.

The same effects as the first embodiment can be obtained by the second embodiment as mentioned above.

Third Embodiment

FIG. 4 is a schematic cross sectional view showing a light emitting layer of a group III nitride semiconductor light emitting element in the third preferred embodiment according to the invention.

As shown in FIG. 4 , an MQW 40 of the group III nitride semiconductor light emitting element of the third embodiment is formed with the light emitting layer comprising a first pair layer 41 to an eighth pair layer 48 , each being formed of a group III nitride semiconductor. A first well layer to an eighth well layer to compose the MQW 40 are each formed under growth conditions to coincide in emission wavelength with each other, as mentioned later. Si is doped as an impurity into the second well layer to the eighth well layer. The amount of the Si doped is set to increase gradually from the n-semiconductor layer side to the p-semiconductor layer side. The thickness of the first well layer to the eighth well layer is set to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The group III nitride semiconductor means at least group III-V nitride semiconductor represented by In x Ga 1−x N (where 0≦x≦1). In x (x: composition ratio) is set to have composition ratios to decrease gradually from the n-semiconductor layer side to the p-semiconductor layer side. The MQW 40 is formed by supplying NH 3 , TMG and TMI into the reactor under a growth temperature condition of 700° C. to 900° C. while using N 2 as a carrier gas.

The first pair layer 41 is composed of the first well layer 41 A and a first barrier layer 41 B, and formed on the n-AlGaN 13 as shown in FIG. 1A . The first well layer 41 A is disposed on the n-semiconductor layer side in relation to the first barrier layer 41 B, and formed of an In 0.29 Ga 0.71 N layer with a thickness of about 42 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The first barrier layer 41 B is disposed on the p-semiconductor layer side in relation to the first well layer 41 A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer 42 is composed of a second well layer 42 A and a second barrier layer 42 B, and formed on the first pair layer 41 . The second well layer 42 A is disposed on the n-semiconductor layer side in relation to the second barrier layer 42 B, and formed of an In 0.26 Ga 0.74 N layer with a thickness of about 39 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The second well layer 42 A is doped with an impurity, silicon (Si) at a doping amount of about 1×10 −7 cm −3 . The second barrier layer 42 B is disposed on the p-semiconductor layer side in relation to the second well layer 42 A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer 43 is composed of a third well layer 43 A and a third barrier layer 43 B, and formed on the second pair layer 42 . The third well layer 43 A is disposed on the n-semiconductor layer side in relation to the third barrier layer 43 B, and formed of an In 0.24 Ga 0.76 N layer with a thickness of about 36 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The third well layer 43 A is doped with an impurity, silicon (Si) at a doping amount of about 2×10 −7 cm −3 . The third barrier layer 43 B is disposed on the p-semiconductor layer side in relation to the third well layer 43 A, and formed of a GaN layer with a thickness of about 5 nm.

A fourth pair layer 44 is composed of a fourth well layer 44 A and a fourth barrier layer 44 B, and formed on the third pair layer 43 . The fourth well layer 44 A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer 44 B, and formed of an In 0.22 Ga 0.78 N layer with a thickness of about 33 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The fourth well layer 44 A is doped with an impurity, silicon (Si) at a doping amount of about 3×10 −7 cm −3 . The fourth barrier layer 44 B is disposed on the p-semiconductor layer side in relation to the fourth well layer 44 A, and formed of a GaN layer with a thickness of about 5 nm.

A fifth pair layer 45 is composed of a fifth well layer 45 A and a fifth barrier layer 45 B, and formed on the fourth pair layer 44 . The fifth well layer 45 A is disposed on the n-semiconductor layer side in relation to the fifth barrier layer 45 B, and formed of an In 0.20 Ga 0.80 N layer with a thickness of about 30 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The fifth well layer 45 A is doped with an impurity, silicon (Si) at a doping amount of about 4×10 −7 cm −3 . The fifth barrier layer 45 B is disposed on the p-semiconductor layer side in relation to the fifth well layer 45 A, and formed of a GaN layer with a thickness of about 5 nm.

A sixth pair layer 46 is composed of a sixth well layer 46 A and a sixth barrier layer 46 B, and formed on the fifth pair layer 45 . The sixth well layer 46 A is disposed on the n-semiconductor layer side in relation to the sixth barrier layer 46 B, and formed of an In 0.18 Ga 0.82 N layer with a thickness of about 27 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The sixth well layer 46 A is doped with an impurity, silicon (Si) at a doping amount of about 5×10 −7 cm −3 . The sixth barrier layer 46 B is disposed on the p-semiconductor layer side in relation to the sixth well layer 46 A, and formed of a GaN layer with a thickness of about 5 nm.

A seventh pair layer 47 is composed of a seventh well layer 47 A and a seventh barrier layer 47 B, and formed on the sixth pair layer 46 . The seventh well layer 47 A is disposed on the n-semiconductor layer side in relation to the seventh barrier layer 47 B, and formed of an In 0.16 Ga 0.84 N layer with a thickness of about 24 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The seventh well layer 47 A is doped with an impurity, silicon (Si) at a doping amount of about 6×10 −7 cm −3 . The seventh barrier layer 47 B is disposed on the p-semiconductor layer side in relation to the seventh well layer 47 A, and formed of a GaN layer with a thickness of about 5 nm.

The eighth pair layer 48 is composed of an eighth well layer 48 A and an eighth barrier layer 48 B, and formed on the seventh pair layer 47 . The eighth well layer 48 A is disposed on the n-semiconductor layer side in relation to the eighth barrier layer 48 B, and formed of an In 0.14 Ga 0.86 N layer with a thickness of about 21 Å. It is adapted to emit bluish light with an emission wavelength of 460 nm to 463 nm. The eighth well layer 48 A is doped with an impurity, silicon (Si) at a doping amount of about 7×10 −7 cm −3 . The eighth barrier layer 48 B is disposed on the p-semiconductor layer side in relation to the eighth well layer 48 A, and formed of a GaN layer with a thickness of about 5 nm.

The In (indium) composition ratio, thickness and Si doping concentration of the first well layer 41 A to the eighth well layer 48 A are as shown in Table 3.

The same effects as the first embodiment can be obtained by the third embodiment as mentioned above.

Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

For example, the following modifications can be made according to the invention.

(1) In the above embodiments, the composition ratios of the plural InGaN well layers are set different from each other such that emission wavelengths thereof coincide with each other. However, the invention is not limited to this. For example, the plural InGaN well layers may comprise different bandgap widths. In this case, it is desired that the bandgap width of the plural well layers increases gradually from the n-semiconductor layer side to the p-semiconductor layer side.

(2) In the above embodiments, the light emitting layer (i.e., MQW layer) has 4, 6 or 8 pair layers. However, the invention is not limited to this. The number of the pair layers can be arbitrarily changed on condition that the pair layers are formed such that a barrier layer is stacked on the p-semiconductor layer side of a well layer.

(3) In the above embodiments, the barrier layer of each pair layer is formed of GaN. However, the invention is not limited to this. For example, the barrier layer may be formed of GaN-based semiconductor comprising at least a composition ratio represented by Al x Ga 1−x N (where 0≦x≦ 1 ).

(4) In the above embodiments, the group III nitride semiconductor light emitting element is an LED element. However, the invention is not limited to this. For example, it may be an LD element.