Group III intride semiconductor light emitting element

A group III nitride semiconductor light emitting element, comprising having a light emitting layer with a multiquantum well structure formed of a group III nitride semiconductor. The light emitting layer has plural well layers, and the plural well layers are formed to coincide in emission wavelength with each other.

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

BACKGROUND OF THE INVENTION

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 InxGa1−xN 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.

SUMMARY OF THE INVENTION

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, andthe 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

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

As shown inFIG. 1A, the group III nitride semiconductor light emitting element1comprises a p-side electrode18and an n-side electrode19, and further comprises an AlN buffer layer11grown on a sapphire substrate under low-temperature growth conditions, an Si-doped n+-GaN layer12, an Si-doped n-AlGaN layer13, an MQW14with a multiquantum well structure formed of InGaN/GaN, an Mg-doped p-AlGaN layer15, an Mg-doped p+-GaN layer16, and a current spreading layer17as 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 layer11is formed by supplying trimethylgallium (TMG) into a reactor in which the sapphire substrate10is placed under a growth temperature condition of 350° C. to 550° C. (preferably 400° C. to 550° C.) while using H2as a carrier gas.

The n+-GaN layer12and the p+-GaN layer16are formed by supplying NH3and trimethylgallium (TMG) into the reactor under a growth temperature condition of 1100° C. while using H2as a carrier gas. Monosilane as an Si source is used for a dopant to provide n-type conductivity with the n+-GaN layer12, and cyclopentadienyl magnesium (Cp2Mg) as an Mg source used for a dopant to provide p-type conductivity with the p+-GaN layer16.

The n-AlGaN layer13and the p-AlGaN layer15are formed by supplying NH3, TMG and trimethylaluminum (TMA) into the reactor under a temperature condition of 1100° C. SiH4as an Si source is used for a dopant to provide n-type conductivity with the n-AlGaN layer13, and cyclopentadienyl magnesium (Cp2Mg) as an Mg source used for a dopant to provide p-type conductivity with the p-AlGaN layer15.

As shown inFIG. 1B, the MQW14is formed with a light emitting layer comprising a first pair layer21to a fourth pair layer24, each being formed of a group III nitride semiconductor. A first well layer to a fourth well layer to compose the MQW14are 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 InxGa1−xN (where 0≦x≦1). Inx(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 MQW14is formed by supplying NH3, TMG and trimethylindium (TMI) into the reactor under a growth temperature condition of 700° C. to 900° C. while using N2as a carrier gas.

The first pair layer21is composed of the first well layer21A and a first barrier layer21B, and formed on the n-AlGaN13. The first well layer21A is disposed on the n-semiconductor layer side in relation to the first barrier layer21B, and formed of an In0.26Ga0.74N 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 layer21B is disposed on the p-semiconductor layer side in relation to the first well layer21A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer22is composed of a second well layer22A and a second barrier layer22B, and formed on the first pair layer21. The second well layer22A is disposed on the n-semiconductor layer side in relation to the second barrier layer22B, and formed of an In0.23Ga0.77N 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 layer22A is doped with an impurity, silicon (Si) at a doping amount of about 2×10−7cm−3. The second barrier, layer22B is disposed on the p-semiconductor layer side in relation to the second well layer22A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer23is composed of a third well layer23A and a third barrier layer23B, and formed on the second pair layer22. The third well layer23A is disposed on the n-semiconductor layer side in relation to the third barrier layer23B, and formed of an In0.20Ga0.80N 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 layer23A is doped with an impurity, silicon (Si) at a doping amount of about 4×10−7cm−3. The third barrier layer23B is disposed on the p-semiconductor layer side in relation to the third well layer23A, and formed of a GaN layer with a thickness of about 5 nm.

The fourth pair layer24is composed of a fourth well layer24A and a fourth barrier layer24B, and formed on the third pair layer23. The fourth well layer24A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer24B, and formed of an In0.17Ga0.83N 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 layer24A is doped with an impurity, silicon (Si) at a doping amount of about 6×10−7cm−3. The fourth barrier layer24B is disposed on the p-semiconductor layer side in relation to the fourth well layer24A, 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 layer21A to the fourth well layer24A are as shown in Table 1.

The current spreading layer17is disposed on the p+-GaN layer16, and formed of a transparent electrode made of Indium tin oxide (ITO).

The p-side electrode18is formed on the surface of the current spreading layer17, and the n-side electrode19is formed on the surface of the n+-GaN layer12exposed by etching.

In applying a voltage from a power source to the group III nitride semiconductor light emitting element1thus structured, light emitted from the MQW14is observed where an emission spectrum with a sharp emission wavelength peak (emission wavelength: 460 nm to 463 nm) is confirmed. This is as shown inFIG. 2Awhere the vertical axis indicates emission intensity and the horizontal axis indicates wavelength. As shown inFIG. 2A, the emission spectrum observed has an FWHM (=full-width at half-maximum) of 20 nm.

In contrast, as shown inFIG. 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 inFIGS. 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 layer21to the fourth well layer24are 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. 3is 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 inFIG. 3, an MQW30of the group III nitride semiconductor light emitting element of the second embodiment is formed with the light emitting layer comprising a first pair layer31to a sixth pair layer36, each being formed of a group III nitride semiconductor. A first well layer to a sixth well layer to compose the MQW30are 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 InxGa1−xN (where 0≦x≦1). Inx(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 MQW30is formed by supplying NH3, TMG and TMI into the reactor under a growth temperature condition of 700° C. to 900° C. while using N2as a carrier gas.

The first pair layer31is composed of the first well layer31A and a first barrier layer31B, and formed on the n-AlGaN13as shown inFIG. 1A. The first well layer31A is disposed on the n-semiconductor layer side in relation to the first barrier layer31B, and formed of an In0.26Ga0.74N 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 layer31B is disposed on the p-semiconductor layer side in relation to the first well layer31A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer32is composed of a second well layer32A and a second barrier layer32B, and formed on the first pair layer31. The second well layer32A is disposed on the n-semiconductor layer side in relation to the second barrier layer32B, and formed of an In0.24Ga0.76N 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 layer32A is doped with an impurity, silicon (Si) at a doping amount of about 1×10−7cm−3. The second barrier layer32B is disposed on the p-semiconductor layer side in relation to the second well layer32A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer33is composed of a third well layer33A and a third barrier layer33B, and formed on the second pair layer32. The third well layer33A is disposed on the n-semiconductor layer side in relation to the third barrier layer33B, and formed of an In0.22Ga0.78N 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 layer33A is doped with an impurity, silicon (Si) at a doping amount of about 2×10−7cm−3. The third barrier layer33B is disposed on the p-semiconductor layer side in relation to the third well layer33A, and formed of a GaN layer with a thickness of about 5 nm.

A fourth pair layer34is composed of a fourth well layer34A and a fourth barrier layer34B, and formed on the third pair layer33. The fourth well layer34A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer34B, and formed of an In0.20Ga0.80N 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 layer34A is doped with an impurity, silicon (Si) at a doping amount of about 3×10−7cm−3. The fourth barrier layer34B is disposed on the p-semiconductor layer side in relation to the fourth well layer34A, and formed of a GaN layer with a thickness of about 5 nm.

A fifth pair layer35is composed of a fifth well layer35A and a fifth barrier layer35B, and formed on the fourth pair layer34. The fifth well layer35A is disposed on the n-semiconductor layer side in relation to the fifth barrier layer35B, and formed of an In0.18Ga0.82N 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 layer35A is doped with an impurity, silicon (Si) at a doping amount of about 4×10−7cm−3. The fifth barrier layer35B is disposed on the p-semiconductor layer side in relation to the fifth well layer35A, and formed of a GaN layer with a thickness of about 5 nm.

The sixth pair layer36is composed of a sixth well layer36A and a sixth barrier layer36B, and formed on the fifth pair layer35. The sixth well layer36A is disposed on the n-semiconductor layer side in relation to the sixth barrier layer36B, and formed of an In0.16Ga0.84N 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 layer36A is doped with an impurity, silicon (Si) at a doping amount of about 5×10−7cm−3. The sixth barrier layer36B is disposed on the p-semiconductor layer side in relation to the sixth well layer36A, 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 layer31A to the sixth well layer36A 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. 4is 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 inFIG. 4, an MQW40of the group III nitride semiconductor light emitting element of the third embodiment is formed with the light emitting layer comprising a first pair layer41to an eighth pair layer48, each being formed of a group III nitride semiconductor. A first well layer to an eighth well layer to compose the MQW40are 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 InxGa1−xN (where 0≦x≦1). Inx(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 MQW40is formed by supplying NH3, TMG and TMI into the reactor under a growth temperature condition of 700° C. to 900° C. while using N2as a carrier gas.

The first pair layer41is composed of the first well layer41A and a first barrier layer41B, and formed on the n-AlGaN13as shown inFIG. 1A. The first well layer41A is disposed on the n-semiconductor layer side in relation to the first barrier layer41B, and formed of an In0.29Ga0.71N 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 layer41B is disposed on the p-semiconductor layer side in relation to the first well layer41A, and formed of a GaN layer with a thickness of about 5 nm.

A second pair layer42is composed of a second well layer42A and a second barrier layer42B, and formed on the first pair layer41. The second well layer42A is disposed on the n-semiconductor layer side in relation to the second barrier layer42B, and formed of an In0.26Ga0.74N 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 layer42A is doped with an impurity, silicon (Si) at a doping amount of about 1×10−7cm−3. The second barrier layer42B is disposed on the p-semiconductor layer side in relation to the second well layer42A, and formed of a GaN layer with a thickness of about 5 nm.

A third pair layer43is composed of a third well layer43A and a third barrier layer43B, and formed on the second pair layer42. The third well layer43A is disposed on the n-semiconductor layer side in relation to the third barrier layer43B, and formed of an In0.24Ga0.76N 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 layer43A is doped with an impurity, silicon (Si) at a doping amount of about 2×10−7cm−3. The third barrier layer43B is disposed on the p-semiconductor layer side in relation to the third well layer43A, and formed of a GaN layer with a thickness of about 5 nm.

A fourth pair layer44is composed of a fourth well layer44A and a fourth barrier layer44B, and formed on the third pair layer43. The fourth well layer44A is disposed on the n-semiconductor layer side in relation to the fourth barrier layer44B, and formed of an In0.22Ga0.78N 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 layer44A is doped with an impurity, silicon (Si) at a doping amount of about 3×10−7cm−3. The fourth barrier layer44B is disposed on the p-semiconductor layer side in relation to the fourth well layer44A, and formed of a GaN layer with a thickness of about 5 nm.

A fifth pair layer45is composed of a fifth well layer45A and a fifth barrier layer45B, and formed on the fourth pair layer44. The fifth well layer45A is disposed on the n-semiconductor layer side in relation to the fifth barrier layer45B, and formed of an In0.20Ga0.80N 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 layer45A is doped with an impurity, silicon (Si) at a doping amount of about 4×10−7cm−3. The fifth barrier layer45B is disposed on the p-semiconductor layer side in relation to the fifth well layer45A, and formed of a GaN layer with a thickness of about 5 nm.

A sixth pair layer46is composed of a sixth well layer46A and a sixth barrier layer46B, and formed on the fifth pair layer45. The sixth well layer46A is disposed on the n-semiconductor layer side in relation to the sixth barrier layer46B, and formed of an In0.18Ga0.82N 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 layer46A is doped with an impurity, silicon (Si) at a doping amount of about 5×10−7cm−3. The sixth barrier layer46B is disposed on the p-semiconductor layer side in relation to the sixth well layer46A, and formed of a GaN layer with a thickness of about 5 nm.

A seventh pair layer47is composed of a seventh well layer47A and a seventh barrier layer47B, and formed on the sixth pair layer46. The seventh well layer47A is disposed on the n-semiconductor layer side in relation to the seventh barrier layer47B, and formed of an In0.16Ga0.84N 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 layer47A is doped with an impurity, silicon (Si) at a doping amount of about 6×10−7cm−3. The seventh barrier layer47B is disposed on the p-semiconductor layer side in relation to the seventh well layer47A, and formed of a GaN layer with a thickness of about 5 nm.

The eighth pair layer48is composed of an eighth well layer48A and an eighth barrier layer48B, and formed on the seventh pair layer47. The eighth well layer48A is disposed on the n-semiconductor layer side in relation to the eighth barrier layer48B, and formed of an In0.14Ga0.86N 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 layer48A is doped with an impurity, silicon (Si) at a doping amount of about 7×10−7cm−3. The eighth barrier layer48B is disposed on the p-semiconductor layer side in relation to the eighth well layer48A, 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 layer41A to the eighth well layer48A are as shown in Table 3.

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

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 AlxGa1−xN (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.