JP4284946B2 - Nitride semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor light emitting device, and more particularly to a nitride semiconductor light emitting device having a small threshold current and a large slope efficiency.
[0002]
[Prior art]
The gallium nitride-based light emitting device is a semiconductor light emitting device composed of a mixed crystal compound semiconductor containing GaN, In, and Al, and the lattice constant of the compound semiconductor increases in the order of AlN, GaN, and InN.
Conventionally, when fabricating a 405 nm gallium nitride semiconductor laser device 90, for example, as shown in FIG. 7, an n-GaN buffer layer 92, an n-AlGaN cladding layer 93, and a GaN light guide are formed on a sapphire substrate or GaN substrate 91. A layer 94, an active layer 95, a GaN light guide layer 96, a p-AlGaN cladding layer 97, and a p-GaN contact layer 98 are stacked.
Here, although not illustrated, the active layer 95 is configured as a quantum well structure including an InGaN well layer and an InGaN barrier layer having a larger band gap energy than the well layer, and the In composition of the well layer and the barrier layer is respectively 8% and 2%.
[0003]
When the active layer is crystal-grown with the structure of the above laminated structure, the well layer and the barrier layer constituting the active layer have a lattice constant larger than that of GaN, but strain is introduced into the well layer. In the wavelength band of 405 nm, since the In composition of the well layer is low, a phenomenon in which lattice defects are generated from the interface between the compound semiconductor layers or from within each compound semiconductor layer hardly occurs.
[0004]
[Problems to be solved by the invention]
By the way, in order to fabricate a semiconductor laser device having a blue band (wavelength of 460 nm) or a green band (wavelength of 510 nm) with such a laminated structure composed of nitride-based compound semiconductor layers, the In composition of the InGaN well layer is , 20% and 30%.
However, when the In composition of the InGaN well layer is increased to 20% or 30% in order to increase the emission wavelength, the lattice constant of the InGaN well layer increases, and the well layer and the barrier layer constituting the active layer Distortion occurs in the interface of the above or in the film of the well layer.
As a result, there is a problem that lattice defects are introduced and the luminous efficiency is deteriorated. This is because when a lattice defect is introduced, when a current is injected to emit light, the lattice defect functions as a non-emission center and the light emission efficiency deteriorates.
In addition, since distortion occurs, the phase separation into a phase with a large In composition and a phase with a small In composition occur in the well layer, so that the light emission efficiency at a predetermined light emission wavelength deteriorates.
[0005]
For example, in order to emit light at 460 nm, an In _X3 Ga _{1 -X3} N (X3 = 0.18) well layer with a thickness of 25 mm and an In _X1 Ga _{1 -X1} N (X1 = 0.02) barrier with a thickness of 50 mm In the conventional quantum well structure composed of layers, when the in-plane distribution of the cathode minescence intensity of the active layer is observed, as shown in FIG. 8, a non-light emitting region A (black region) that does not emit light of 460 nm is obtained. ) Exists in large numbers. FIG. 8 is a copy of the cathode minescence intensity in-plane distribution, and the original photograph has been submitted to the JPO as a reference photograph.
When the non-light emitting region overlaps the laser stripe, the threshold value of the semiconductor laser element is increased and the slope efficiency is deteriorated.
[0006]
Accordingly, an object of the present invention is to provide a nitride-based semiconductor light-emitting device having an active layer having a quantum well structure with good crystallinity and high light emission efficiency.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a nitride-based semiconductor light-emitting device according to the present invention (hereinafter referred to as a first invention) has a quantum well structure active layer made of a nitride-based compound semiconductor layer containing In. In a physical semiconductor light emitting device,
The strain compensation layer having a band gap energy larger than the band gap energy of the barrier layer constituting the quantum well structure includes at least one well layer and the at least one well layer among the well layers constituting the quantum well structure. It is characterized by being interposed between the barrier layers.
[0008]
In the first invention, although it is preferable that a strain compensation layer is interposed between all well layers and both barrier layers sandwiching the well layers, at least one well layer and both barriers sandwiching the at least one well layer are provided. A strain compensation layer may be interposed between the layers.
The composition of all strain compensation layers does not have to be the same, and the composition of the two strain compensation layers interposed between the well layer and both barrier layers sandwiching the well layer may be different from each other.
[0009]
Another nitride-based semiconductor light-emitting device according to the present invention (hereinafter referred to as a second invention) is a nitride-based semiconductor light-emitting device having an active layer having a quantum well structure composed of a nitride-based compound semiconductor layer containing In. ,
A strain compensation layer having a band gap energy larger than that of the barrier layer constituting the quantum well structure is interposed in the barrier layer or the well layer.
[0010]
In the second invention, although it is preferable to interpose a strain compensation layer in every barrier layer or well layer, a strain compensation layer is interposed in at least one barrier layer or in at least one well layer. May be.
The composition of all strain compensation layers does not have to be the same. For example, even if the composition of at least two barrier layers among the barrier layers interposed in each barrier layer or each well layer is different from each other, good.
[0011]
The first and second inventions can be applied as long as the active layer has a quantum well structure made of a nitride-based compound semiconductor layer containing In. For example, when the well layer and the barrier layer are composed of InGaN layers, the strain compensation layer is an AlGaN layer having Al instead of In.
[0012]
The strain compensation layer is not necessarily interposed between the well layer and the barrier layer, in the well layer, or in the barrier layer, but may be interposed in the light guide layer.
That is, another nitride-based semiconductor light-emitting device according to the present invention (hereinafter referred to as a third invention) is a nitride-based semiconductor light-emitting device having an active layer having a quantum well structure composed of a nitride-based compound semiconductor layer containing In. In the element
A strain compensation layer having a band gap energy larger than the band gap energy of both the light guide layer and the barrier layer constituting the quantum well structure is provided in at least one of the light guide layers provided above and below the active layer. It is characterized by intervening.
[0013]
In a preferred embodiment of the third invention, a plurality of strain compensation layers are periodically interposed in the light guide layer. When the light guide layer is composed of an InGaN layer, the strain compensation layer is an AlGaN layer having Al instead of In.
[0014]
In a preferred embodiment of the first to third inventions, the strain compensation layer is thinner than both the well layer and the barrier layer. Thereby, it is possible to prevent the strain compensation layer from affecting the optical characteristics of the nitride-based semiconductor light-emitting element.
In the first to third aspects of the invention, the nitride semiconductor laser element is a semiconductor laser element having a laminated structure of nitride compound semiconductor layers. A nitride-based compound semiconductor has nitrogen (N) as a group V and has a composition of Al _a B _b G _c In _d N _x P _y As _z (a + b + c + d = 1, 0 ≦ a, b, c, d ≦ 1, x + y + z = 1, 0 <x ≦ 1, 0 ≦ y, z ≦ 1).
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below specifically and in detail with reference to the accompanying drawings. It should be noted that the film formation method, the composition and thickness of the compound semiconductor layer, and the like shown in the following embodiment examples are merely examples for facilitating the understanding of the present invention, and the present invention is limited to these examples. It is not a thing.
Embodiment 1
This embodiment is an example of an embodiment in which the nitride-based semiconductor light-emitting device according to the first invention is applied to a GaN-based semiconductor laser device. FIG. 1 shows the activity of the GaN-based semiconductor laser device of this embodiment. FIG. 2 is a cross-sectional view showing the configuration in the vicinity of the layer, and FIG. 2 is a band structure diagram in the vicinity of the active layer.
The GaN-based semiconductor laser device of the present embodiment is a semiconductor laser device having an emission wavelength of 460 nm, and the structure 10 near the active layer has a lower GaN light guide layer 12 having a thickness of 80 nm, as shown in FIG. The barrier layer 14, the strain compensation layer 16 </ b> A, the well layer 18, and the strain compensation layer 16 </ b> B are composed of three periods, the barrier layer 14, and the upper GaN light guide layer 20 having a thickness of 80 nm.
[0016]
The barrier layer 14 is an In _X1 Ga _{1 -X1} N (X1 = 0.02) layer having a thickness of 50 mm, and the strain compensation layer 16 is an Al _X2 Ga _{1 -X2} N (X2 = 0.04) layer having a thickness of 10 mm. The well layer 18 is configured as an In _X3 Ga _{1 -X3} N (X3 = 0.18) layer having a thickness of 25 mm.
In this embodiment, the strain compensation layer 16 is interposed between all the well layers 18 and the adjacent barrier layers 14. As shown in FIG. 2, the band gap energy of the strain compensation layers 16A, B is larger than the band gap energy of the barrier layer 14, and the lattice constant in the free standing of the strain compensation layers 16A, B is Smaller than that.
[0017]
Observing the in-plane distribution of the cathode minescence intensity of the active layer having the active layer structure of Embodiment 1, as shown in FIG. 3, the entire region emits light at 460 nm, and no non-light emitting region exists. Compared with the in-plane distribution of the cathode minence intensity of the conventional active layer shown in FIG. 8, the effect of the present invention can be fully recognized. FIG. 3 shows a copy of the cathode minescence intensity in-plane distribution. The original photo was submitted to the JPO as a reference photo.
In the present embodiment example, when the active layer is crystal-grown, the strain compensation layer 16 is interposed between the well layer 18 and the barrier layer 14 so that the accumulation of strain is alleviated, so that crystal defects are hardly generated. Thus, the non-light emitting area is reduced.
As a result, the threshold value of the nitride-based semiconductor laser device having the structure 10 in the vicinity of the active layer of this embodiment is lowered, and the slope efficiency is improved.
[0018]
In this embodiment, the strain compensation layers 16A and 16B are AlGaN layers. However, the present invention is not limited to this, and the strain compensation layers 16A and B may be composed of InAlGaN layers as long as the band gap energy is larger than that of the barrier layer 14. In the present embodiment, the strain compensation layers 16A and 16B have the same film thickness and the same composition, but may have different compositions and film thicknesses.
In this embodiment, the strain compensation layer 16 is interposed between all the well layers 18 and the barrier layer 14 sandwiching the well layers 18. However, the present invention is not limited to this. May be interposed between the barrier layer 14 and the barrier layer 14.
Furthermore, the active layer is not limited to a three-period quantum well structure.
[0019]
In this embodiment, the barrier layer 14 is an InGaN layer, but may be composed of a quaternary mixed crystal InAlGaN layer.
Moreover, although the light guide layers 12 and 20 are GaN layers, they are not limited to GaN, and any of InGaN, AlGaN, and InAlGaN may be used, and a structure in which they are stacked may be used. The light guide layers 12 and 20 do not have to be the same. For example, the Al and In compositions may be different or the film thicknesses may be different, and one may be a single layer film and the other may be a laminated film. good.
[0020]
Embodiment 2
This embodiment is an example of an embodiment in which the nitride-based semiconductor light-emitting device according to the second invention is applied to a GaN-based semiconductor laser device, and FIG. 4 is a band structure diagram in the vicinity of the active layer.
The GaN-based semiconductor laser device of the present embodiment is a semiconductor laser device having an emission wavelength of 460 nm, and the structure 30 in the vicinity of the active layer includes a lower GaN light guide layer 32 having a thickness of 80 nm, as shown in FIG. The barrier layer 34, the strain compensation layer 36 provided in the barrier layer 34, and the three periods of the well layer 38, the barrier layer 34, and the upper GaN light guide layer 40 having a thickness of 80 nm are included.
[0021]
The compositions of the barrier layer 34, the strain compensation layer 36, and the well layer 38 are the same as those in the first embodiment.
As shown in FIG. 3, the band gap energy of the strain compensation layer 36 is larger than the band gap energy of the barrier layer 34, and the lattice constant in the free standing of the strain compensation layer 36 is smaller than that of the barrier layer 34.
[0022]
In the present embodiment example, when the active layer is crystal-grown, the strain compensation layer 36 is interposed in the barrier layer 34, so that the accumulation of strain is alleviated, so that crystal defects are generated and reduced. Similarly, the non-light emitting area is reduced.
As a result, the threshold value of the nitride-based semiconductor laser device having the structure 30 in the vicinity of the active layer of this embodiment is lowered, and the slope efficiency is improved.
[0023]
Embodiment 3
The present embodiment is another example of an embodiment in which the nitride-based semiconductor light-emitting device according to the second invention is applied to a GaN-based semiconductor laser device, and FIG. 5 is a band structure diagram in the vicinity of the active layer.
The GaN-based semiconductor laser device of the present embodiment is a semiconductor laser device having an emission wavelength of 460 nm, and the structure 50 in the vicinity of the active layer includes a lower GaN light guide layer 52 having a thickness of 80 nm, as shown in FIG. The barrier layer 54, the well layer 56, the strain compensation layer 58 provided in the well layer 56, the barrier layer 54, and the upper GaN light guide layer 60 having a thickness of 80 nm are configured.
[0024]
The compositions of the barrier layer 54, the well layer 56, and the strain compensation layer 58 are the same as those in the first embodiment.
As shown in FIG. 5, the band gap energy of the strain compensation layer 58 is larger than the band gap energy of the barrier layer 54, and the lattice constant in the free standing of the strain compensation layer 58 is smaller than that of the barrier layer 54.
[0025]
In this embodiment example, when the active layer is crystal-grown, the strain compensation layer 58 is interposed in the well layer 56, so that the accumulation of strain is alleviated, so that crystal defects are less likely to occur. Similarly, the non-light emitting area is reduced.
As a result, the threshold value of the nitride-based semiconductor laser device having the structure 50 in the vicinity of the active layer of this embodiment is lowered, and the slope efficiency is improved.
[0026]
Embodiment 4
This embodiment is an example of an embodiment in which the nitride-based semiconductor light-emitting device according to the third invention is applied to a GaN-based semiconductor laser device, and FIG. 6 is a band structure diagram in the vicinity of the active layer.
The GaN-based semiconductor laser device of the present embodiment is a semiconductor laser device having an emission wavelength of 460 nm, and the structure 70 in the vicinity of the active layer includes a lower GaN light guide layer 72 having a thickness of 80 nm, as shown in FIG. The active layer 74 has a multiple quantum well structure and an upper GaN light guide layer 76 having a thickness of 80 nm.
[0027]
In this embodiment, a plurality of strain compensation layers 78 are interposed in the lower and upper GaN light guide layers 72 and 76, respectively.
The average composition of the GaN light guide layers 72 and 76 is In _x Ga ₁ -XN (X = 0.02), and as shown in FIG. In each case, an Al _X1 Ga _{1 -X1} N (X1 = 0.04) strain compensation layer 78 having a thickness of 10 mm is interposed with a period of 200 mm.
[0028]
As shown in FIG. 6, the band gap energy of the strain compensation layer 78 is larger than the band gap energy of the GaN light guide layers 72 and 76, and the lattice constant in the free standing of the strain compensation layer 78 is GaN light guide layer 72. And less than that of 76.
[0029]
In the present embodiment example, since the strain compensation layer 78 is interposed in the light guide layers 72 and 76, strain accumulation is mitigated during crystal growth of the active layer, so that crystal defects are less likely to occur. Non-light emitting areas are reduced.
As a result, the threshold value of the nitride-based semiconductor laser device having the light guide layer structure of this embodiment is lowered, and the slope efficiency is improved.
[0030]
In this embodiment, a strain compensation layer may be interposed between the well layer and the barrier layer in addition to the light guide layers 72 and 76.
That is, as shown in FIG. 6, the active layer 74 having a multiple quantum well structure has an In _X3 Ga _{1 -X3} N (X3 = 0.18) well layer 80 with a thickness of 25 mm and a thickness of 50 mm with the well layer 80 interposed therebetween. In _X2 Ga _{1 -X2} N (X2 = 0.08) barrier layer 82 and a well layer 80 and a barrier layer 82 on both sides of the well layer 80 with a thickness of 10 mm Al _X4 Ga _{1 -X4} N (X4 = 0.04) It is composed of strain compensation layers 84A and 84B.
As shown in FIG. 6, the band gap energy of the strain compensation layer 84 is larger than the band gap energy of the barrier layer 82, and the lattice constant in the free standing of the strain compensation layer 84 is smaller than that of the barrier layer 82.
Thereby, in this embodiment, the effect of the present invention is further increased.
[0031]
【The invention's effect】
According to the first and second inventions, the strain compensation layer having a band gap energy larger than the band gap energy of the barrier layer is interposed between the well layer and both the barrier layers sandwiching the well layer, or the strain compensation By interposing the layer in the well layer or the barrier layer, the strain accumulation is reduced during crystal growth of the active layer, thereby suppressing the generation of crystal defects and reducing the non-light emitting region.
According to the third aspect of the present invention, the strain compensation layer having a band gap energy larger than the band gap energy of the light guide layer is interposed in the light guide layer, thereby reducing the accumulation of strain, thereby Generation | occurrence | production is suppressed and the non-light-emission area | region is reduced.
By applying the nitride semiconductor light emitting device according to the first to third inventions, a nitride semiconductor laser device having a small threshold current, an increased slope efficiency, and a high light emission efficiency at a predetermined light emission wavelength In addition, it is possible to realize a nitride-based light emitting diode with high emission efficiency at a constant emission wavelength.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration in the vicinity of an active layer of a GaN-based semiconductor laser device according to Embodiment 1;
2 is a band structure diagram in the vicinity of an active layer of a GaN-based semiconductor laser device according to Embodiment 1; FIG.
FIG. 3 is a copy of a photograph of an in-plane distribution of cathode minence intensity.
4 is a band structure diagram in the vicinity of an active layer of a GaN-based semiconductor laser device according to Embodiment 2. FIG.
5 is a band structure diagram in the vicinity of an active layer of a GaN-based semiconductor laser device according to Embodiment 3. FIG.
6 is a band structure diagram in the vicinity of an active layer of a GaN-based semiconductor laser device according to Embodiment 4. FIG.
FIG. 7 is a cross-sectional view of a 405 nm semiconductor laser device.
FIG. 8 is a copy of a photograph of the cathode minescence intensity in-plane distribution.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Structure near the active layer of the GaN-based semiconductor laser device of Example 1 12 ... Lower GaN light guide layer, 14 ... Barrier layer, 16 ... Strain compensation layer, 18 ... Well layer, 20 ... ... upper GaN light guide layer, 30 ... structure near the active layer of the GaN-based semiconductor laser device of Embodiment 2, 32 ... lower GaN light guide layer, 34 ... barrier layer, 36 ... strain compensation layer, 38 ... Well layer, 40... Upper GaN light guide layer, 50... Structure near the active layer of the GaN-based semiconductor laser device of Embodiment 3, 52... Lower GaN light guide layer, 54. ...... Well layer, 58 …… Strain compensation layer, 60 …… Upper GaN light guide layer, 70 …… Structure near the active layer of the GaN-based semiconductor laser device of Embodiment 4, 72 …… Lower GaN light guide layer, 74 …… Active layer with multiple quantum well structure, 76 …… GaN optical guide layer, 78... Strain compensation layer, 80... Well layer, 82... Barrier layer, 84 .. strain compensation layer, 90... 405 nm semiconductor laser element, 91. 92... N-GaN buffer layer, 93... N-AlGaN cladding layer, 94... GaN light guide layer, 95... Active layer, 96. ... p-GaN contact layer.

Claims (7)

The well layer and the barrier layer have an active layer having a quantum well structure composed of an InGaN layer,
A strain compensation layer composed of an AlGaN layer is interposed between at least one well layer of the well layers constituting the quantum well structure and both barrier layers sandwiching the at least one well layer ;
A blue or green band nitride-based semiconductor light-emitting device in which the AlGaN layer has a thickness smaller than both the thickness of the well layer and the thickness of the barrier layer . The nitride-based semiconductor light-emitting element according to claim 1, wherein a laminated structure including a nitride-based compound semiconductor layer including the active layer is provided on a sapphire substrate. The light guide layer made of an InGaN layer is provided above and below the active layer, and a strain compensation layer made of an AlGaN layer is interposed in at least one light guide layer of the light guide layer. Nitride-based semiconductor light emitting device. The nitride-based semiconductor light-emitting element according to claim 3, wherein a plurality of the AlGaN layers are periodically interposed in the light guide layer. The nitride-based semiconductor light-emitting device according to claim 4, wherein the AlGaN layer is periodically interposed in the light guide layer with a period of 200 μm. The nitride-based semiconductor light-emitting element according to claim 5, wherein the thickness of the AlGaN layer in the light guide layer is 10 mm. The nitride-based semiconductor light-emitting element according to claim 6, wherein the thickness of the AlGaN layer of the active layer is 10 mm.

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