JP2000332364A - Nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To greatly reduce piezo electric field effect, and to obtain a GaN-based semiconductor device with large light-emitting efficiency by performing inclined doping for reducing the concentration of impurities monotonously or in steps to the barrier layer of an MQW active layer. SOLUTION: A buffer layer 2 is deposited onto a substrate 1 for increasing temperature, thus sequentially laminating an AlGaN layer 3, an nAlGaN cladding layer 4, an nGaN light guide layer 5, a multiple quantum well(MQW) active layer 8, and a pGaN contact layer 9. In this case, the concentration of Si that is n-type impurities in the band structure of the MQW active layer 6 and a barrier layer is reduced from 5×1018 cm-3 or the like successively or in steps. Also, doping is made merely at the side of the substrate (an n- cladding side). In either case, it is important that the concentration of the Si at the n-cladding side is high. Doping is made in this manner, thus greatly and effectively canceling a piezo electric field being generated by strain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor light emitting device such as a semiconductor laser expected to be applied to the field of optical information processing and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A nitride semiconductor having nitrogen (N) as a group V element has been regarded as a promising material for short-wavelength light emitting devices because of its large band gap. Of these gallium nitride-based compound semiconductor (GaN-based semiconductor: Al _x Ga _y In _z
N (0 ≦ x, y, z ≦ 1, x + y + z = 1) has been actively studied, and a blue light emitting diode (LED) and a green LED
Has been put to practical use. In addition, a semiconductor laser having an oscillation wavelength in the 400 nm band has been eagerly desired for increasing the capacity of the optical disk device, and a semiconductor laser using a GaN-based semiconductor as a material has attracted attention and is now reaching a practical level.

FIG. 4 shows GaN in which laser oscillation is achieved.
1 is a structural sectional view of a semiconductor laser. Sapphire substrate 4
01 on a metalorganic vapor phase epitaxy (MOVPE) method.
aN buffer layer 402, n-GaN layer 403, n-AlG
aN clad layer 404, n-GaN optical guide layer 405, G
a multiple quantum well (MQW) active layer 406 made of a _1-x In _x N / Ga _1-y In _y N (0 <y <x <1);
Light guide layer 407, p-AlGaN cladding layer 408, p-
A GaN contact layer 409 is grown. And p-Ga
A ridge stripe having a width of about 3 μm is formed on the N contact layer 409, and both sides are buried with SiO ₂ 411. Then ridge stripe and S
A p electrode 41 made of, for example, Ni / Au on iO ₂ 411
0, and an n-electrode 412 made of, for example, Ti / Al
Is formed. In this element, the n-electrode 412 is grounded,
When a voltage is applied to the p-electrode 410, the MQW active layer 406
Holes from the p-electrode 410 side and the n-electrode 4
Electrons are injected from the side 12 to generate an optical gain in the MQW active layer 406, and cause laser oscillation in an oscillation wavelength band of 400 nm. Ga _1-x I which is the material of the MQW active layer 406
_{n x N / Ga 1-y} In y N oscillation wavelength by the composition and thickness of the thin film changes. At present, continuous oscillation at room temperature or higher is realized.

By controlling the width and height of the ridge stripe, the laser is designed to oscillate in the fundamental mode in the horizontal transverse mode. That is, by providing a difference in the light confinement coefficient between the fundamental transverse mode and the higher-order mode (first-order or higher mode), oscillation in the fundamental transverse mode is enabled.

[0005]

The well layer of the MQW active layer is subjected to in-plane compressive strain in the horizontal direction. A nitride semiconductor is a material having a large piezoelectric effect, and an internal electric field is generated when compressive strain is applied (called a piezo electric field effect). For example, GaN grown on sapphire substrate
In a system semiconductor, the outermost surface of the crystal becomes a nitrogen surface, and an internal electric field (piezo electric field) is generated from the crystal surface toward the sapphire substrate. In the GaN-based semiconductor laser shown in FIG. 4, an electric field is generated in the direction shown in FIG.

Due to the internal electric field, the band is tilted in the well layer as shown in FIG. As a result, electrons and holes are spatially separated, and the luminous efficiency is reduced.

In GaN-based light emitting devices, recently, Si
Is added to the active layer. Si doping distributes carriers (electrons) in the well layer, and acts in a direction to cancel the internal electric field by the screening effect. However, it is difficult to completely cancel the internal electric field, and a problem remains.

The present invention has been made in view of the above circumstances, and provides a GaN-based semiconductor device that can greatly reduce the piezoelectric field effect and has high luminous efficiency. It is particularly effective in application to lasers for optical disks.

[0009]

In the GaN-based semiconductor device of the present invention, a gradient doping is applied to the barrier layer of the MQW active layer such that the impurity concentration decreases monotonically or stepwise.

[0010] In the nitride semiconductor device of the present invention, the outermost surface of the crystal is a nitrogen surface, and an n-type impurity is added to the barrier layer of the MQW active layer so as to increase the amount on the n-cladding side.

Further, the nitride semiconductor device of the present invention can
A p-type impurity is added to the barrier layer of the W active layer so as to increase the p-cladding side.

The GaN-based semiconductor device of the present invention has
The well layer of the QW active layer is subjected to graded doping in which the impurity concentration is gradually reduced in the well layer, so that a piezoelectric field effect generated by compressive stress can be effectively reduced, and a nitride semiconductor having a large luminous efficiency. An element can be obtained.

Further, in the GaN-based semiconductor device of the present invention, the outermost surface of the crystal is a nitrogen surface, and an n-type impurity is added to the well layer of the MQW active layer so as to increase the p-cladding side.

The GaN-based semiconductor device according to the present invention has
A p-type impurity is added to the well layer of the QW active layer so that the n-cladding side is increased.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. The production method of the present invention
The growth method of the nitride semiconductor is not limited to the MOVPE method, but has been proposed for growing a nitride semiconductor layer such as a hydride vapor phase epitaxy method (H-VPE method) or a molecular beam epitaxy method (MBE method). The method can be applied to all methods.

(Embodiment 1) FIG. 1 is a structural sectional view of a GaN-based semiconductor laser showing an embodiment of the present invention. The method for manufacturing the laser shown in FIG. 1 is as follows.

First, an organic metal and ammonia (NH ₃ ) are supplied on a sapphire substrate 1 at 500 ° C. to deposit a buffer layer 2. Thereafter, the temperature is raised, and tri-methyl gallium (TMG), monosilane (SiH ₄ ), tri-methyl aluminum (TMA), etc. are supplied to supply n-Al _0.15
Ga _0.85 N layer 3, n-Al _0.07 Ga _0.93 N cladding layer 4,
An n-GaN optical guide layer 5, a multiple quantum well (MQW) active layer 6, a p-GaN optical guide layer 7, a p-Al _0.07 Ga _0.93 N cladding layer 8, and a p-GaN contact layer 9 are sequentially stacked. p-GaN contact layer 9 and p-Al _0.07 Ga
_{The 0.93} N cladding layer 8 is used to control the horizontal and transverse modes.
It is processed into a ridge stripe shape. The stripe width is about 3-5 microns. p-GaN contact layer 9
A p-electrode 10 is formed thereon, and the side wall of the ridge is an insulating film 1.
Covered with 1. A wiring electrode 12 is provided on the surface of the p-electrode 10 in the opening of the insulating film 11 and on a part of the insulating film 11. An n-electrode 13 is formed on the surface etched until a part of the n-Al _0.15 Ga _0.85 N layer 3 is exposed.

In this device, when a voltage is applied between the n-electrode 13 and the p-electrode 10, holes are injected from the p-electrode 10 toward the MQW active layer 6, and electrons are injected from the n-electrode 13. It produces gain and causes laser oscillation at a wavelength of 405 nm. The MQW active layer 6 is made of Ga having a thickness of 3.5 nm.
It is composed of a _0.8 In _0.2 N well layer and a GaN barrier layer having a thickness of 10 nm.

FIG. 2 shows the band structure of the MQW active layer and the impurity concentration profile in the barrier layer of the device shown in FIG. Here, Si (silicon) which is an n-type impurity is shown as an example. In (a), the Si concentration is 5 × 10 ¹⁸ cm ^−3.
Has been decreasing continuously. In (b), it decreases on the stairs. In (c), only the substrate side (n clad side) is doped. In any of (a) to (c),
It is important that the Si concentration on the n-cladding side is high. Doping in this manner has a great effect on canceling out a piezo electric field caused by distortion. As a result, as shown in the band structure of FIG. 2, a flat band is formed, and the luminous efficiency can be maintained at a high level.

When a sapphire substrate is used, the outermost surface is N
Since a piezo electric field is generated from the p side to the n side, the Si concentration on the n clad layer side is high as shown in FIGS. 2 (a) to 2 (c). In the opposite case, ie G
In the case of the a-plane, the doping profile is reversed.

When a p-type impurity, for example, Mg is used, the profile shown in FIGS.
That is, by increasing the Mg concentration on the p-cladding layer side, the piezo electric field can be effectively canceled.

In the present invention, Si is used as an n-type impurity and Mg is used as a p-type impurity. The reason is that these dopants form a relatively shallow impurity level in the GaN-based crystal, and are also effective in canceling the piezo electric field since impurity diffusion hardly occurs.

In the present invention, since the piezoelectric field can be canceled very effectively, problems such as a decrease in the luminous efficiency and an increase in the threshold current of the semiconductor laser, which occur in the conventional GaN-based light emitting device, occur. Without doing so, a nitride semiconductor device having good characteristics can be obtained. It is particularly effective in application to lasers for optical disks.

(Embodiment 2) In Embodiment 1, the case where doping is performed on the barrier layer in the MQW active layer has been described because generation of a piezoelectric field can be canceled. Here, a case where the well layer is doped will be described.

FIG. 3 shows the band structure of the MQW active layer of this device and the impurity concentration profile in the well layer.
Here, Si (silicon) which is an n-type impurity is shown as an example. In (a), the Si concentration continuously increases to 5 × 10 ¹⁸ cm ⁻³ . In (b), it increases on the stairs. In (c), only the p-cladding side is doped. In any of (a) to (c), it is important that the Si concentration on the p-cladding side is high. Doping in this manner has a great effect on canceling out the piezoelectric field caused by the compressive stress. When a sapphire substrate is used, the outermost surface is the N-plane, and a piezo electric field is generated from the p-side to the n-side.
As shown in the figure, the Si concentration on the p-cladding layer side is high.

In the opposite case, that is, in the case of a Ga plane, the doping profile is also reversed.

When a p-type impurity, for example, Mg is used, the profile shown in FIGS.
That is, by increasing the Mg concentration on the n-cladding layer side, the piezoelectric field can be effectively canceled.

In the present invention, since the piezoelectric field can be canceled very effectively, problems such as a decrease in the luminous efficiency and an increase in the threshold current of the semiconductor laser, which occur in the conventional GaN-based light emitting device, occur. Without doing so, a nitride semiconductor device having good characteristics can be obtained. It is particularly effective in application to lasers for optical disks.

Although the present invention has been described with reference to a GaN-based semiconductor laser as an example, the present invention has a great effect when growing an active region such as a light emitting diode.

Although the first and second embodiments have been described, it is needless to say that the effect of the present invention is great even if these two are combined.

[0031]

As described above, according to the GaN-based semiconductor device of the present invention, the piezo-electric field effect generated by the compressive stress can be effectively reduced by performing the gradient doping on the barrier layer of the MQW active layer, and the light emission is improved. A highly efficient nitride semiconductor device can be obtained. It is particularly effective in application to lasers for optical disks.

In the GaN-based semiconductor device of the present invention, the outermost surface of the crystal is a nitrogen surface, and an n-type impurity is added to the barrier layer of the MQW active layer so as to increase the n-cladding side.

Alternatively, in the GaN-based semiconductor device of the present invention, a p-type impurity is added to the barrier layer of the MQW active layer so as to increase the p-cladding side. By doping in this way, the piezo electric field caused by the strain can be canceled very effectively, and the luminous efficiency seen in the conventional GaN-based light emitting device and the threshold current of the semiconductor laser increase. It is possible to obtain a nitride semiconductor device having good characteristics without causing any problem.

Further, the GaN-based semiconductor device of the present invention
The graded doping is applied to the well layer of the QW active layer,
The piezoelectric field effect generated by the compressive stress can be effectively reduced, and a nitride semiconductor device with high luminous efficiency can be obtained.

In the GaN-based semiconductor device of the present invention, the outermost surface of the crystal is a nitrogen surface, and n-type impurities are added to the well layer of the MQW active layer so as to increase the p-cladding side.

Alternatively, in the GaN-based semiconductor device of the present invention, the p-type impurity is added to the well layer of the MQW active layer so that the n-clad side is increased. By doping in this way, the piezoelectric field generated by the strain can be effectively canceled, and the problems such as a decrease in the luminous efficiency and an increase in the threshold current of the semiconductor laser seen in the conventional GaN-based light-emitting device can be achieved. Does not occur, and a nitride semiconductor device having good characteristics can be obtained. It is particularly effective in application to lasers for optical disks.

[Brief description of the drawings]

FIG. 1 is a sectional view of an element of a GaN-based semiconductor laser showing a first embodiment of the present invention;

FIG. 2 is a diagram showing a band diagram of an MQW active layer and an impurity profile of a barrier layer according to the present invention.

FIG. 3 is a diagram showing a band diagram of an MQW active layer and an impurity profile of a well layer according to the present invention.

FIG. 4 is a sectional view of a conventional GaN-based quantum well semiconductor laser device;

FIG. 5 shows MQW of a conventional GaN-based quantum well semiconductor laser.
Active layer band diagram

[Explanation of symbols]

_Reference Signs _List 1 sapphire substrate 2 buffer layer 3 n-Al _0.15 Ga _0.85 N layer 4 n-Al _0.07 Ga _0.93 N cladding layer 5 n-GaN optical guide layer 6 MQW active layer 7 p-GaN optical guide layer 8 p-Al _0.07 Ga _0.93 N cladding layer 9 p-GaN contact layer 10 p electrode 11 insulating film 12 wiring electrode 13 n electrode 401 sapphire substrate 402 buffer layer 403 n-GaN layer 404 n-AlGaN cladding layer 405 n-GaN optical guide layer 406 MQW active layer 407 p -GaN optical guide layer 408 p-AlGaN cladding layer 409 p-GaN contact layer 410 p electrode 411 SiO ₂ 412 n electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Kume 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Terms (reference) 5F073 AA13 AA45 AA74 BA05 CA07 CB14 EA29

Claims (10)

[Claims] 1. A nitride semiconductor device comprising: an active layer; and a cladding layer sandwiching the active layer, wherein the active layer has a multiple quantum well structure including a barrier layer and a well layer. Is a nitride semiconductor device to which an impurity is added, and the concentration of the impurity is gradually reduced in the barrier layer. 2. A nitride semiconductor device comprising: an active layer; and a clad layer sandwiching the active layer, wherein the active layer has a multiple quantum well structure including a barrier layer and a well layer. Is a nitride semiconductor device in which an impurity is added, and the concentration of the impurity changes stepwise in the barrier layer. 3. A nitride semiconductor device comprising an active layer and a clad layer sandwiching the active layer, wherein the outermost surface of the nitride semiconductor crystal is a nitrogen surface, A nitride semiconductor device in which an n-type impurity is added to a barrier layer of a multiple quantum well active layer so as to increase the number of n-cladding sides. 4. A nitride semiconductor device comprising an active layer and a cladding layer sandwiching the active layer, wherein the outermost surface of the nitride semiconductor crystal is a nitrogen surface, A nitride semiconductor device in which a p-type impurity is added to a barrier layer of a multiple quantum well active layer so as to increase the p-cladding side. 5. A nitride semiconductor device comprising: an active layer; and a cladding layer sandwiching the active layer, wherein the active layer has a multiple quantum well structure including a barrier layer and a well layer. Is a nitride semiconductor device to which an impurity is added, and the concentration of the impurity is gradually reduced in the well layer. 6. A nitride semiconductor device comprising: an active layer; and a clad layer sandwiching the active layer, wherein the active layer has a multiple quantum well structure including a barrier layer and a well layer. Is a nitride semiconductor device to which an impurity is added, and the concentration of the impurity changes stepwise in the well layer. 7. A nitride semiconductor device comprising an active layer and a clad layer sandwiching the active layer, wherein the outermost surface of the nitride semiconductor crystal is a nitrogen surface, and A nitride semiconductor device in which an n-type impurity is added to a well layer of a multiple quantum well active layer so as to increase the p-cladding side. 8. A nitride semiconductor device comprising an active layer and a clad layer sandwiching the active layer, wherein the outermost surface of the nitride semiconductor crystal is a nitrogen surface, A nitride semiconductor device in which a p-type impurity is added to a well layer of a multiple quantum well active layer so as to increase the number of n-cladding sides. 9. The nitride semiconductor device according to claim 3, wherein the n-type impurity is silicon. 10. The nitride semiconductor device according to claim 4, wherein the p-type impurity is magnesium.