JPH1022586A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device using a low-threshold current density and long-life nitride III-V compound semiconductor. SOLUTION: A GaN semiconductor laser is constructed by sequentially depositing an n-type GaN layer 2, an n-type InGaN light absorbing layer 3, an n-type AlGaN clad layer 4, an n-type GaN light waveguide layer 5, an active layer 6 of InGaN, a p-type GaN light waveguide layer 7, a p-type AlGaN clad layer 8, a p-type InGaN light absorbing layer 9 and a p-type GaN layer 10, on a c-surface sapphire substrate 1. The compositional ratio of In of the n-type InGaN light absorbing layer 3 and the p-type InGaN light absorbing layer 9 is higher than that of the active layer 6 of InGaN, such that these n-type InGaN light absorbing layer 3 and the p-type InGaN light absorbing layer 9 absorb light of an emission wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device which is suitably applied to a semiconductor light emitting device using a nitride III-V compound semiconductor such as GaN.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a semiconductor laser capable of emitting light at a short wavelength in order to increase the recording / reproducing density or the resolution of an optical disk or a magneto-optical disk which performs recording / reproducing using a laser beam. Research is being actively conducted for practical use.

FIG. 4 shows an example of a GaN-based semiconductor laser which has been actively studied recently as such a semiconductor laser. As shown in FIG. 4, in this GaN-based semiconductor laser, an n-type GaN layer 102, an n-type AlGaN cladding layer 103, and an n-type GaN optical waveguide are formed on a c-plane sapphire substrate 101 via a GaN buffer layer (not shown). Wave layer 10
4. Active layer 105 made of InGaN, p-type GaN optical waveguide layer 106, p-type AlGaN cladding layer 107 and p-type
Type GaN layers 108 are sequentially stacked. Where n
The GaN layer 102 is used not only as a contact layer for an n-side electrode (not shown) but also as a buffer layer. The p-type GaN layer 108 is used as a contact layer for a p-side electrode (not shown).

[0004] However, according to the findings of the present inventors,
The conventional GaN-based semiconductor laser shown in FIG. 4 described above has a problem when the laser structure is considered optically. that is,
This is because GaN is transparent to light having an oscillation wavelength in the blue-violet band of the GaN-based semiconductor laser.

That is, FIG. 5 shows a result obtained by calculation of an optical field during operation of the GaN-based semiconductor laser shown in FIG. However, in this calculation, the oscillation wavelength is set to 4
10 nm, the In composition ratio of the active layer 105 made of InGaN is 0.2, the thickness is 5 nm, the refractive index is 2.7, and n-type Al is used.
The Al composition ratio of the GaN cladding layer 103 and the p-type AlGaN cladding layer 107 is 0.15, the thickness is 1 μm, the refractive index is 2.45, the n-type GaN optical waveguide layer 104 and the p-type G
The thickness of the aN optical waveguide layer 106 is 0.1 μm, and the refractive index is 2.
54, the thickness of the n-type GaN layer 102 is 3 μm, the refractive index is 2.54, and the refractive index of the c-plane sapphire substrate 101 is 1.6.
It was set to 5. As can be seen from FIG. 5, the light generated in the laser resonator is pulled by the n-type GaN layer 102, so that most of the light is concentrated on the n-type GaN layer 102. In this case, the light confinement coefficient of this laser structure becomes very small (10 ^{-10 in} this example), and a large gain is required to cause laser oscillation. This is because, if the gain required for oscillation is g, the optical confinement coefficient is Γ, and the loss of the laser resonator is α _loss , then Γg = α _loss . From this equation, if the loss is constant, the gain required for oscillation is This is because it is inversely proportional to the light confinement coefficient.

On the other hand, recently, pulsed laser oscillation at room temperature has been reported for GaN-based semiconductor lasers (for example, Nikkei Electronics, January 15, 1996).
JP, page 13). The GaN-based semiconductor laser does not have an optical field as shown in FIG. The reason is,
The active layer is composed of an InGaN well layer having a thickness of 2.5 nm and an InG well layer.
This is because the multiple quantum well structure in which the aN barrier layer and the aN barrier layer are stacked for 26 periods is designed to be sufficiently thick so that the effective refractive index of the optical field is larger than that of GaN. In this case, the light confinement coefficient is as large as 0.34.

However, in this GaN-based semiconductor laser, since the total thickness of the InGaN well layers constituting the active layer is as large as 2.5 × 26 = 65 nm, the threshold current density is high, and the life of the device itself and the electrode life are reduced. Is disadvantageous to the life of the device. In fact, the above-mentioned documents point out that the reliability of the electrode is a problem. Also, this G
In an aN-based semiconductor laser, since the thickness of the active layer exceeds the critical thickness, mismatched dislocations enter the active layer, and the characteristics and life of the device are deteriorated. Further, since a large number of quantum wells exist in the active layer, it is expected that non-uniform current injection will occur (see FIG. 6). Further, from the viewpoint of the optical design of the semiconductor laser, there is a restriction that the effective refractive index cannot be made smaller than that of GaN. Therefore, the degree of freedom of design is required when controlling a far-field image (FFP). Is small and inconvenient.

[0008]

From the above, it is necessary to devise a structure to increase the light confinement coefficient and prevent the active layer from exceeding the critical film thickness. Has not been proposed before.

Therefore, an object of the present invention is to provide a nitride III-V having a low threshold current density, a long life, and easy control of a far-field image by improving the distribution of an optical field during operation.
An object of the present invention is to provide a semiconductor light emitting device using a group III compound semiconductor.

[0010]

In order to achieve the above object, the present invention provides a semiconductor light emitting device using a nitride III-V compound semiconductor, wherein at least a light absorbing layer for absorbing light having an emission wavelength is provided. It is characterized by having more.

In the present invention, the semiconductor light emitting device is
Specifically, it has a structure in which an active layer is sandwiched between an n-type cladding layer and a p-type cladding layer, and has a light absorption layer on at least one of the outside of the n-type cladding layer and the outside of the p-type cladding layer. In this case, the outside of the n-type cladding layer and p
When a light absorbing layer is provided on both sides of the mold cladding layer, n
There are cases where the light absorbing layer is provided only outside the mold cladding layer, and cases where the light absorbing layer is provided only outside the p-type cladding layer.

In the present invention, InGa is used as an active layer.
When an N layer is used, typically, an InGaN layer having a larger In composition ratio than the InGaN layer forming the active layer is used as the light absorbing layer. Specifically, for example, when an active layer having an In composition ratio of 0.2 is used, an InGaN layer having an In composition ratio larger than 0.2 is used as a light absorption layer.

In the present invention, the light absorbing layer is a GaN layer doped with both a donor impurity (eg, Si) and an acceptor impurity (eg, Mg or Zn) (an InGaN layer having an In composition ratio of 0). May be used. In this case, the light absorption band by the donor-acceptor pair generated in the GaN layer is 400 to 500 nm.
Occurs nearby. Further, for example, as a donor impurity, S
i, Mg is used as an acceptor impurity, and its doping concentration is represented by [Si] and [Mg], respectively.
By setting [Si]> [Mg] or [Mg]> [Si], the conductivity type of the GaN layer can be controlled.

By utilizing the above-described generation of a donor-acceptor pair by doping with a donor impurity and an acceptor impurity, the limitation on the In composition ratio of the InGaN layer as the light absorbing layer can be relaxed. Specifically, In
In whose composition ratio is smaller than 0.2 (for example, 0.05)
Even a GaN layer can be used as a light absorption layer by utilizing the generation of a donor-acceptor pair.

In the present invention, an AlGaInN layer or the like may be used as the light absorbing layer in addition to the above-described ones. If necessary, the formation of a donor-acceptor pair by doping with a donor impurity and an acceptor impurity may be further performed. May be used.

In the present invention, the nitride III-V compound semiconductor is composed of at least one group III element selected from the group consisting of Al, Ga and In and N, and some specific examples are given below. , GaN, AlGa
N, InGaN or the like.

The semiconductor light-emitting device according to the present invention having the above-described structure has a light-absorbing layer that absorbs light having an emission wavelength. The field distribution can be improved so that the peak of the light field distribution is located substantially near the active layer. For this reason, a large light confinement coefficient can be obtained. Further, since it is not necessary to form the active layer thick to increase the light confinement coefficient, the thickness of the active layer can be suppressed to a critical thickness or less.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding portions are denoted by the same reference numerals.

FIG. 1 shows a G according to a first embodiment of the present invention.
1 shows an aN-based semiconductor laser. As shown in FIG. 1, in the GaN-based semiconductor laser according to the first embodiment,
On a c-plane sapphire substrate 1, an n-type GaN layer 2, an n-type InGaN light absorbing layer 3, an n-type AlGaN cladding layer 4, an n-type GaN optical waveguide layer 5, for example, InGaN via a GaN buffer layer not shown. Active layer 6, p-type GaN
Optical waveguide layer 7, p-type AlGaN cladding layer 8, p-type InG
The aN light absorbing layer 9 and the p-type GaN layer 10 are sequentially stacked. Here, the n-type GaN layer 2 is formed of n
In addition to being used as a contact layer for the side electrode, it is also used as a buffer layer. The p-type GaN layer 10 is used as a contact layer for a p-side electrode (not shown).

In the GaN-based semiconductor laser according to the first embodiment, the n-type InGaN light absorbing layer 3 is provided immediately below the n-type AlGaN cladding layer 4, and the p-type AlG
Immediately above the aN cladding layer 8, a p-type InGaN light absorbing layer 9
Is characteristically provided.

FIG. 2 shows GaN according to the first embodiment.
Is a result obtained by calculating an optical field during operation of a system semiconductor laser. However, in this calculation, the oscillation wavelength is 410 nm, the n-type InGaN light absorbing layer 3 and the p-type I
The nGaN light absorbing layer 9 has an In composition ratio of 0.25 and a thickness of 1
The absorption coefficient for light having a wavelength of 0 nm and a wavelength of 410 nm is 10 ⁵
cm ^-1 (0.3 as the extinction coefficient). Also, In
The active layer 6 made of GaN has an In composition ratio of 0.2, a thickness of 5 nm, a refractive index of 2.7, and an n-type AlGaN cladding layer 4.
And the Al composition ratio of the p-type AlGaN cladding layer 8 is 0.1.
15, the thickness is 1 μm, the refractive index is 2.45, and the thickness of the n-type GaN optical waveguide layer 5 and the p-type GaN optical waveguide layer 7 is 0.1 μm.
m, the refractive index is 2.54, and the thickness of the n-type GaN layer 2 is 3 μm.
m, the refractive index was 2.54, and the refractive index of the c-plane sapphire substrate 1 was 1.65. Note that these parameters used in the calculation of the optical field are based on the n-type InGaN light absorbing layer 3 and the p-type IGaN.
Except for the nGaN light absorbing layer 9, the parameters are the same as those used in the calculation of the optical field during the operation of the conventional GaN-based semiconductor laser shown in FIG.

The light confinement coefficient in the light field shown in FIG. 2 is 0.022. The light field shown in FIG.
The G according to the first embodiment except that the aN light absorption layer 3 and the p-type InGaN light absorption layer 9 are not provided.
The conventional G of the same structure as the aN-based semiconductor laser shown in FIG.
Compared with the optical field during the operation of the aN-based semiconductor laser, it is understood that the optical field is concentrated near the active layer 6 and the distribution of the optical field is greatly improved. Thus, n-type I
The provision of the nGaN light-absorbing layer 3 and the p-type InGaN light-absorbing layer 9 significantly improves the light field because the n-type InGaN light-absorbing layer 3 and the p-type InGaN
Since the loss of the light field is increased by the GaN light absorbing layer 9,
This is due to the fact that the light field itself changes to a light field with a smaller loss.

In order to manufacture the GaN-based semiconductor laser according to the first embodiment, each layer is grown on the c-plane sapphire substrate 1 by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). It should be done.

As described above, according to the GaN-based semiconductor laser according to the first embodiment, the n-type InGaN light absorbing layer 3 is provided immediately below the n-type AlGaN cladding layer 4, and the p-type AlGaN cladding layer 8 is provided. P-type InG just above
By providing the aN light absorption layer 9, the distribution of the light field during operation can be significantly improved as compared with the conventional case, and a high light confinement coefficient can be obtained. Therefore, the threshold current density can be significantly reduced.
Further, thereby, heat generation during operation can be reduced, and reliability can be improved (internal deterioration can be prevented). Further, since the thickness of the active layer 6 can be reduced, a reduction in threshold current density, a reduction in heat generation in the electrode portion, particularly in a contact portion of the p-side electrode, and an improvement in electrode reliability can be achieved. In addition, since the thickness of the active layer 6 can be set to be equal to or less than the critical thickness, it is possible to prevent the occurrence of mismatch dislocations in the active layer 6 and to improve the characteristics and life of the device.

As described above, a GaN-based semiconductor laser emitting blue-violet light with low threshold current density, high reliability and long life can be realized. Further, in this GaN-based semiconductor laser, there is no restriction that the effective refractive index of the light field cannot be made smaller than that of GaN as in the conventional GaN-based semiconductor laser, and the GaN-based semiconductor laser is used for controlling a far-field image (FFP). Large design freedom.

FIG. 3 shows G according to a second embodiment of the present invention.
1 shows an aN-based semiconductor laser. As shown in FIG. 2, in the GaN-based semiconductor laser according to the second embodiment,
n-type InG only under the n-type AlGaN cladding layer 4
The aN light absorbing layer 3 is provided, and the p-type GaN layer 10 is not provided. Other configurations are the same as those of the GaN-based semiconductor laser according to the first embodiment, and a description thereof will not be repeated.

The optical field during operation of the GaN-based semiconductor laser according to the second embodiment was obtained by calculation in the same manner as in the first embodiment, and was substantially the same as that shown in FIG. The coefficient was 0.022 as in the first embodiment. According to the second embodiment, various advantages similar to those of the first embodiment can be obtained.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various modifications based on the technical idea of the present invention are possible.

For example, the first embodiment and the second embodiment
The numerical values given in the embodiment are merely examples, and different numerical values may be used as needed. In the first and second embodiments described above,
Although the In composition ratio of the n-type InGaN light absorbing layer 3 and the p-type InGaN light absorbing layer 9 is 0.25, a different value of the In composition ratio may be used. Furthermore, these n
An undoped InGaN light absorbing layer may be used instead of the p-type InGaN light absorbing layer 3 and the p-type InGaN light absorbing layer 9. Also, instead of the c-plane sapphire substrate 1, Ga
An N substrate, a SiC substrate, or the like may be used.

In the first and second embodiments described above, the case where the present invention is applied to a GaN-based semiconductor laser has been described.
It is also possible to apply to an N-based light emitting diode.

[0031]

As described above, the semiconductor light emitting device according to the present invention has at least one light absorbing layer that absorbs light of an emission wavelength, thereby reducing the distribution of the light field during operation as compared with the prior art. Thus, it is possible to realize a semiconductor light emitting device using a nitride III-V compound semiconductor, which has a low threshold current density, a long life, and easy control of a far-field image.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a GaN-based semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing an optical field during operation of the GaN-based semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a configuration of a GaN-based semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a configuration of a conventional GaN-based semiconductor laser.

FIG. 5 is a schematic diagram illustrating an optical field during operation of a conventional GaN-based semiconductor laser.

FIG. 6 is a schematic diagram for explaining a problem of a conventional GaN-based semiconductor laser.

[Explanation of symbols]

1 ... c-plane sapphire substrate, 2 ... n-type GaN layer,
3 ... n-type InGaN light absorbing layer, 4 ... n-type AlG
aN cladding layer, 6 ... active layer, 8 ... p-type AlG
aN cladding layer, 9... p-type InGaN light absorbing layer, 1
0 ... p-type GaN layer

Claims (6)

[Claims] 1. A semiconductor light emitting device using a nitride III-V compound semiconductor, comprising at least one light absorbing layer for absorbing light having an emission wavelength. 2. An active layer sandwiched between an n-type cladding layer and a p-type cladding layer, wherein the light absorbing layer is provided on at least one of the outside of the n-type cladding layer and the outside of the p-type cladding layer. 2. The semiconductor light emitting device according to claim 1, wherein: 3. The semiconductor light emitting device according to claim 1, wherein said light absorbing layer is an InGaN layer. 4. The semiconductor light emitting device according to claim 1, wherein said light absorbing layer is a GaN layer doped with a donor impurity and an acceptor impurity. 5. An n-type GaN layer, a light absorption layer made of InGaN, an n-type clad layer made of AlGaN, an n-type optical waveguide layer made of GaN, an active layer made of InGaN, and a p-type light guide made of GaN on a substrate. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device has a structure in which a wave layer, a p-type clad layer made of AlGaN, the light absorption layer made of InGaN, and a p-type GaN layer are sequentially stacked. 6. An n-type GaN layer, an optical absorption layer made of InGaN, an n-type clad layer made of AlGaN, an n-type optical waveguide layer made of GaN, an active layer made of InGaN, and a p-type light guide made of GaN on a substrate. Wave layer and AlGaN
2. The semiconductor light-emitting device according to claim 1, wherein the semiconductor light-emitting device has a structure in which p-type cladding layers comprising