JP2002359439A - Method for manufacturing nitride system semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nitride system semiconductor light-emitting element, having an In-containing layer whose In-composition is high, and whose in-composition fluctuation is small, and whose crystallinity is satisfactory as an active layer. SOLUTION: A GaN buffer layer 14, an n-type GaN contact layer 16, an n-type AlGaN clad layer 18, and an n-type GaN optical waveguide layer 20 are grown on a sapphire substrate 12, in the same way as in the conventional manner. Then, a Ga1-x Inx N well layer (x=0.22)/Ga1-y Iny N barrier layer (y=0.02), constituting an active layer 22 are grown in a nitride atmosphere at a growth temperature of 800 deg.C using MOCVD method. At the time of growth, the pressure division of raw gas, such as In is adjusted, so that the growth rate of the GaInN layer can be made higher than that of the optical waveguide layer, and that the agglomerate energy of the GaInN layer is made large. Then, a p-type GaN optical waveguide layer 24, a p-type AlGaN clad layer 26, and a p-type GaN contact layer 28 are grown, in the same way as in the conventional manner. At the growing of the optical waveguide layer 24, the growth rate of the optical waveguide layer is made the same or lower than that of the n-type optical waveguide layer 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a nitride-based semiconductor light-emitting device, and more particularly, to a method for manufacturing an I-type semiconductor light-emitting device having a high In composition, a small fluctuation of the In composition, and good crystallinity.
The present invention relates to a method for manufacturing a nitride-based semiconductor light emitting device having an n-containing layer as an active layer.

[0002]

2. Description of the Related Art In the field of optical recording, there is a demand for practical use of a semiconductor laser device that emits light in a short wavelength range in order to improve the recording density of an optical recording medium such as an optical disk. Thus, nitride III-V compound semiconductors, particularly G
GaN-based semiconductor laser devices using gallium nitride (GaN) -based III-V compound semiconductors such as aN, AlGaN mixed crystals, and GaInN mixed crystals have been actively studied. GaN-based compound semiconductors have a forbidden band width of 1.9.
a direct transition semiconductor ranging from eV to 6.2 eV,
As a material that can realize a semiconductor light emitting device that emits light in a wavelength range from the visible light region to the ultraviolet light region, a semiconductor laser device and a light emitting diode (LED) that emit light in a short wavelength range from green to blue, and even ultraviolet light are realized. It is a compound semiconductor that has attracted attention as a material that can be used.

In addition, nitride III-V compound semiconductors have attracted attention as materials for electronic devices such as field effect transistors (FETs) because of their high saturation electron velocity and high breakdown electric field. In particular, a GaN-based compound semiconductor is also desirable as a material for an electron transit element such as an FET. For example, the saturated electron velocity of GaN is about 2.5 × 1
It is 0 ⁷ cm / s, larger than Si, GaAs and SiC, and has a breakdown electric field of about 5 × 10 ⁶ V / cm, which is second only to diamond. Since GaN-based compound semiconductors have such excellent characteristics, they are considered promising as materials for high-frequency, high-temperature, high-power electron transit devices.

Here, a configuration of a GaN-based semiconductor laser device will be described with reference to FIG. FIG. 2 is a sectional view showing the configuration of the GaN-based semiconductor laser device. A GaN-based semiconductor laser device is a semiconductor laser device provided with a resonator having a stacked structure of a GaN-based compound semiconductor layer.
And a compound semiconductor layer containing at least nitrogen (N) as a group V element. GaN-based semiconductor laser device 10
As shown in FIG. 2, a GaN buffer layer 14 and an n-type GaN contact layer 1 are formed on a c-plane sapphire substrate 12.
6, n-type AlGaN cladding layer 18, n-type GaN optical waveguide layer 20, active layer 22, p-type GaN optical waveguide layer 24, p-type A
It has a stacked structure of an lGaN cladding layer 26 and a p-type GaN contact layer 28. The active layer 22 is made of Ga _1-x
In _x N well layer (for example, x = 0.22) / Ga _1-y In
_This is an active layer having a quantum well structure composed of a yN barrier layer (for example, y = 0.02).

A p-type GaN contact layer 28 and a p-type Al
The upper layer portion of the GaN clad layer 26 is etched to form a stripe ridge having a stripe width of, for example, about 2.5 μm. Further, the upper layer of the n-type GaN contact layer 16, the n-type AlGaN cladding layer 18, the n-type G
aN optical waveguide layer 20, active layer 22, p-type GaN optical waveguide layer 2
4 and the remaining layer of the p-type AlGaN cladding layer 26 are etched to form a mesa structure extending in a direction parallel to the stripe ridge extending direction with a width wider than the stripe width.

As an example of the thickness of each GaN-based III-V compound semiconductor layer, the GaN buffer layer 14 has a thickness of 50
nm, the thickness of the n-type GaN contact layer 16 is 3 μm,
The thickness of the n-type GaN optical waveguide layer 20 is 0.1 μm, the thickness of the p-type GaN optical waveguide layer 24 is 0.1 μm, and the thickness of the p-type AlGaN cladding layer 26 is 0.5 μm. The thickness is 0.5 μm, and the thickness of the p-type GaN contact layer 28 is 0.5 μm.

On the p-type GaN contact layer 28, a p-side electrode 30 made of, for example, a Ni / Au film is formed as an ohmic contact electrode. On the n-type GaN contact layer 16 beside the mesa structure, for example, Ti / Al
An n-side electrode 32 made of a film is formed as an ohmic contact electrode.

[0008] Nitride-based materials such as the above-mentioned GaN-based compound semiconductors
In general, a nitride-based semiconductor light-emitting device such as a semiconductor laser device or a light-emitting diode using a III-V compound semiconductor is generally known as MOCVD (Metal-organic Chemical Vapor Depth).
The nitride-based III-V compound semiconductor layer is grown on a substrate using a vapor phase growth method such as an osition (organic metal chemical vapor deposition) method.

By MOCVD, a layer containing no indium such as a GaN layer or an AlGaN mixed crystal layer (hereinafter referred to as a “GaN layer” or “AlGaN mixed crystal layer”)
When growing an In-free layer), the growth temperature is optimally about 1000 ° C. or higher because of the decomposition of the nitrogen raw material.

For example, in the GaN-based semiconductor laser device 10 described above, a nitride-based II having a composition ratio of In to Ga of 9% is used.
By using an IV group compound semiconductor, a semiconductor light emitting device having an emission wavelength of about 405 nm can be manufactured. By the way, the color of the laser light having a wavelength of about 405 nm is blue-violet, and in order to manufacture a light-emitting device that emits blue or green which is one of the three primary colors of light, for example, an In composition of 20% or more is required. A semiconductor light emitting device having an In-free layer in a light emitting region is required.

[0011] GaI, which is frequently used in an active layer of a semiconductor light emitting device that emits blue or green light having a wavelength longer than blue-violet light,
In the nN well layer, the desorption speed of In increases as the growth temperature increases. For example, at a growth temperature on the order of 1000 ° C., In desorbs during growth, which means that GaI
An nN well layer cannot be grown. Therefore, an AlGaN layer is grown at a growth temperature suitable for growing an AlGaN layer having good crystallinity, for example, 1000 ° C., and then, for example, a GaInN layer containing In is removed with a small amount of In.
It grows at 00-800 ° C. A growth temperature suitable for growing an In-free layer having good crystallinity, for example, 100
Suitably, the In-free layer is grown at 0 ° C.

[0012]

However, 700-80
Even when the GaInN layer is grown at a growth rate of about 0 ° C., as the In composition ratio of the GaInN layer increases,
The composition fluctuation in the layer increases. For example, Ga _0.8 In _0.2
When growing N, the In composition ratio of the Ga _0.8 In _0.2 N layer is as follows:
Instability in the layer and poor uniformity in the layer. Therefore, in practice, it has been difficult to manufacture a nitride-based semiconductor light emitting device having a GaInN mixed crystal layer having a large In composition ratio as an active layer.

Therefore, a nitride-based semiconductor light emitting device containing indium (In) at an In composition ratio exceeding 0.2 with respect to a group 3B element other than In and having a GaInN mixed crystal layer having a uniform composition as an active layer. Development of a method for manufacturing a device is required. Therefore, it is an object of the present invention to provide an In composition having a high In composition, a small fluctuation of the In composition, and good crystallinity.
An object of the present invention is to provide a method for manufacturing a nitride-based semiconductor light emitting device having an n-containing layer as an active layer.

[0014]

Means for Solving the Problems In order to solve the above problems, the present inventor has proposed that the composition ratio of In to Ga is 0.2 or more while maintaining high quality of the crystallinity of the GaInN layer. As a result of intensive studies on a method for producing a uniform GaInN layer without fluctuation of the composition ratio, it was found that the cohesion energy of In is a very important factor of fluctuation of the In composition.

The composition fluctuation of the In composition is caused by the fact that the growth of the In-containing layer is in the form of an island with the progress of three-dimensional growth predominant over two-dimensional growth. The three-dimensional growth proceeds because the cohesive energy of In is small. Conversely, when the cohesive energy is large, layer growth (two-dimensional growth) is easy. As shown in FIG. 3, the cohesive energy of In increases as the growth temperature increases. In other words, the higher the growth temperature, the greater the cohesive energy of In, and the more difficult it is to grow into islands.

As shown in FIG. 4, the cohesive energy decreases as the amount of In in the GaInN layer increases. In other words, the larger the amount of In in the GaInN layer, the smaller the cohesive energy of In and the easier it is to grow like islands.

By the way, in order to obtain a semiconductor light emitting device that emits light of a wavelength of about 460 nm, which is blue, for example, using an In-containing layer as an active layer, the composition ratio of In to Ga is about 22%, The composition ratio is uniquely determined from the emission wavelength. Further, from the viewpoint of crystal quality and the viewpoint of desorption of indium, the growth temperature is restricted to a temperature range of about 700 ° C. or more and 800 ° C. or less. In other words, there are restrictions on increasing the growth temperature, increasing the cohesive energy, and making the progress of layered growth dominant.

Therefore, instead of increasing the growth temperature, S
The cohesion energy of In is adjusted by a method of controlling the binding energy between the In-free base layer and the In-containing layer by the anti-surfactant effect of i, a method of controlling the binding energy by the amount of strain applied to the In-free base layer, and the like. It has been proposed.

The inventor of the present invention has proposed that, when growing an active layer composed of an In-containing layer by a conventional method, the growth rate determined to grow the active layer exactly to a desired thickness is above and below the active layer. It was noted that the growth rate of the provided upper cladding layer and lower cladding layer was considerably lower than that of the provided cladding layer. On the other hand, as shown in FIG. 5, the cohesive energy of In qualitatively increases as the growth rate increases, the progress of island growth of three-dimensional growth becomes inferior, and the growth energy of layer growth of two-dimensional growth increases. Progress becomes dominant.

Therefore, the present inventor has increased the partial pressure of a source gas such as In so as to increase the growth rate of the active layer, which is an In-containing layer, from the cladding layers above and below the active layer. In which has a composition and good crystallinity
With the idea of growing the containing layer invented, the present inventors invented the present invention through repeated experiments.

In order to achieve the above object, based on the above-mentioned findings, the method for manufacturing a nitride-based semiconductor light-emitting device according to the present invention uses a nitride-based group III-V compound semiconductor and a method other than indium. An active layer composed of an In-containing layer containing indium (In) at an indium composition ratio of 0.2 or more with respect to the Group 3B element, and an upper In non-containing layer provided in contact with the upper and lower sides of the active layer. In the method for manufacturing a nitride-based semiconductor light-emitting device having a content layer and a lower In-free layer, the method comprises the steps of:
When the content-containing layer is epitaxially grown at a temperature of 700 ° C. or more and 800 ° C. or less, the growth rate of the In-containing layer and the growth rate of the upper In-free layer are controlled by adjusting the partial pressure of a source gas such as In. The feature is to make it larger than the speed.

In the method of the present invention, a nitride-based semiconductor light-emitting device is a nitride-based semiconductor light emitting device containing nitrogen (N) as a Group 5B element.
V compound semiconductor, specifically _{Al a B b Ga c In d} N
A semiconductor light emitting device having a laminated structure of (a + b + c + d = 1, 0 ≦ a, b, c, d ≦ 1), for example, a nitride-based semiconductor laser device, a nitride-based light-emitting diode, and the like. The In-containing layer refers to a nitride-based III-V compound semiconductor layer containing indium (In) as a Group 3B element and containing nitrogen (N) as a Group 5B element. An In-free layer is a nitride-based layer containing nitrogen (N) as a Group 5B element and not containing indium (In) as a Group 3B element.
A group V compound semiconductor layer.

In the method for fabricating a nitride-based semiconductor light emitting device according to the present invention, the nitride-based III-V compound semiconductor is a GaN-based compound semiconductor, the In-containing layer is a GaInN layer, The present invention can be suitably applied to the production of a nitride-based semiconductor light-emitting device in which the upper In-free layers are (Al) GaN layers. (Al) GaN layer means a GaN layer or an AlGaN layer.

In a further preferred embodiment, the nitride-based semiconductor light emitting device comprises an AlGaN lower cladding layer, a GaN
A GaN-based semiconductor laser device having a laminated structure of a lower optical waveguide layer, an active layer made of GaInN, an upper GaN optical waveguide layer, and an upper AlGaN cladding layer, wherein the MOCV
When the active layer is epitaxially grown at a temperature of 700 ° C. or more and 800 ° C. or less by the method D, the AlGaN lower cladding layer, the GaN lower optical waveguide layer, the GaN upper optical waveguide layer, And A
The growth rate of the active layer is higher than any of the growth rates of the lGaN upper cladding layer. By manufacturing according to the above-described embodiment, a nitride-based semiconductor laser device having a GaInN mixed crystal layer having a band gap energy corresponding to an emission wavelength of 460 nm as an active layer can be manufactured.

[0025]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The film forming method, the composition and thickness of the compound semiconductor layer, the ridge width, the process conditions, and the like described in the following embodiments are merely examples for facilitating understanding of the present invention. It is not limited to this example. Embodiment Example This embodiment is an example of an embodiment in which the method for manufacturing a nitride-based semiconductor light-emitting device according to the present invention is applied to the manufacture of the GaN-based semiconductor laser device 10 described above. (C) shows GaN according to the method of the present embodiment.
FIG. 4 is a cross-sectional view for each step when manufacturing a semiconductor laser element. First, in the same manner as in the conventional method, MOCVD is performed at a growth temperature of 1000 ° C. in a hydrogen atmosphere.
As shown in (a), a GaN buffer layer 14 and an n-type GaN contact layer 1 are formed on a c-plane sapphire substrate 12.
6. The n-type AlGaN cladding layer 18 and the n-type GaN optical waveguide layer 20 are sequentially epitaxially grown.

Next, in the method of this embodiment, n-type Ga
Subsequent to the growth of the N optical waveguide layer 20, a Ga _1-x In _x N well layer (for example, x = 0.22) constituting the active layer 22 at a growth temperature of 800 ° C. and in a nitrogen atmosphere by MOCVD.
/ Ga _1-y In _y N barrier layer (for example, y = 0.02) is grown. During the growth of the active layer 22, the growth rate of the GaInN well layer and the GaInN barrier layer is controlled by adjusting the partial pressure of the source gas such as In.
The growth rate is set higher than 0 so that the cohesive energy of the GaInN layer is increased.

Subsequently, in the same manner as in the conventional method, the MOC
According to the VD method, at a growth temperature of 1000 ° C. in a hydrogen atmosphere,
As shown in FIG. 1C, p-type GaN is formed on the active layer 22.
Optical waveguide layer 24, p-type AlGaN cladding layer 26, and p
Type GaN contact layers 28 are sequentially epitaxially grown. When growing the p-type GaN optical waveguide layer 24, p
The growth rate of the n-type GaN optical waveguide layer 24 is equal to or slower than the growth rate of the n-type GaN optical waveguide layer 20. In this embodiment, the growth rate of the active layer 22 made of a GaInN layer is set to
It was shown that both the well layer having an In composition ratio to Ga of, for example, 0.22 and the barrier layer having, for example, 0.02 have a growth rate higher than that of an adjacent In non-containing layer.
As described in the means for solving the problem of the present inventor, although the growth rate is sufficient in the conventional case at a small stage of the In composition, the present invention is an essential technique in a well layer having a large In composition. It is.

Thereafter, a stripe ridge, a mesa structure, and an electrode are formed in the same manner as in the prior art to form a GaInN mixed crystal having the structure shown in FIG. 2 and having a band gap energy corresponding to an emission wavelength of 460 nm. The GaN-based semiconductor laser device 10 including the active layer 22 can be manufactured.

As described above, the method of the present invention has been specifically described with reference to one example of the embodiment. However, the present invention is not limited to the above-described embodiment, and various methods based on the technical idea of the present invention are possible. Is possible. For example, the numerical values, structures, materials, processes, and the like described in the above-described embodiments are merely examples, and different numerical values, structures, materials, processes, and the like may be used as necessary. Also,
In the embodiment, a sapphire substrate is used as the substrate 12, but if necessary, instead of the sapphire substrate,
A GaN substrate, a SiC substrate, a ZnO substrate, a spinel substrate, or the like may be used. When a conductive substrate such as a GaN substrate or a SiC substrate is used, an electrode can be formed on the back surface of the substrate.

[0030]

According to the method of the present invention, indium (In) is a nitride-based III-V compound semiconductor with an indium composition ratio of 0.2 or more to a group 3B element other than indium. In producing a nitride-based semiconductor light-emitting device having an upper In non-containing layer and a lower In non-containing layer that do not contain indium, which are provided in contact with the active layer composed of the In-containing layer and the active layer, respectively.
The In-containing layer is heated to 700 ° C. or higher by chemical vapor deposition
When epitaxial growth is performed at a temperature of 0 ° C. or less, the growth rate of the In-containing layer is made higher than that of the lower In-free layer and the upper In-free layer by adjusting the partial pressure of a source gas such as In. Thus, a nitride-based semiconductor light-emitting device having a high In composition ratio, a small composition fluctuation, and a structurally and optically high quality In-containing layer as an active layer can be easily manufactured.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (c) are cross-sectional views for respective steps when fabricating a GaN-based semiconductor laser device according to a method 1 of an embodiment.

FIG. 2 is a sectional view showing a configuration of a GaN-based semiconductor laser device.

FIG. 3 is a qualitative diagram showing the relationship between cohesive energy and growth temperature.

FIG. 4 is a qualitative diagram showing the relationship between the cohesive energy and the amount of indium.

FIG. 5 is a qualitative diagram showing the relationship between cohesive energy and growth rate.

[Explanation of symbols]

10 GaN-based semiconductor laser device, 12 sapphire substrate, 14 GaN buffer layer, 16 n-type Ga
N contact layer, 18 n-type AlGaN cladding layer,
20: n-type GaN optical waveguide layer, 22: Ga _1-x In _x N
An active layer composed of a well layer (for example, x = 0.22) / Ga _1-y In _y N barrier layer (for example, y = 0.02), 24...
p-type GaN optical waveguide layer, 26... p-type AlGaN cladding layer, 28... p-type GaN contact layer, 30... p-side electrode, 32.

Claims (3)

[Claims] Each of the nitride-based III-V compound semiconductors comprises an In-containing layer containing indium (In) at an indium composition ratio of at least 0.2 with respect to a group 3B element other than indium. An active layer and an upper layer I which is provided in contact with the upper and lower sides of the active layer and does not contain indium.
A method for manufacturing a nitride-based semiconductor light emitting device having an n-free layer and a lower In-free layer, wherein the In-containing layer is formed at a temperature of 700 ° C.
When epitaxial growth is performed at a temperature of 0 ° C. or less, by adjusting the partial pressure of the In source gas, the growth rate of the In-containing layer is made higher than that of the lower In-free layer and the upper In-free layer. Of manufacturing a nitride-based semiconductor light emitting device. 2. The nitride III-V compound semiconductor is Ga
The nitride-based compound semiconductor according to claim 1, wherein the nitride-based compound semiconductor is an N-based compound semiconductor, the In-containing layer is a GaInN layer, and the lower In-free layer and the upper In-free layer are each an (Al) GaN layer. A method for manufacturing a semiconductor light emitting element. 3. The nitride-based semiconductor light emitting device is an AlGaN
A GaN-based semiconductor laser device having a laminated structure of a lower cladding layer, a GaN lower optical waveguide layer, an active layer made of GaInN, a GaN upper optical waveguide layer, and an AlGaN upper cladding layer, wherein the active layer is formed at 700 ° C. by MOCVD. At the time of epitaxial growth at a temperature of not less than 800 ° C. and less than 800 ° C., by adjusting the partial pressure of the In source gas, the AlGaN lower cladding layer, the GaN lower optical waveguide layer, the GaN upper optical waveguide layer, and the A
2. The method according to claim 1, wherein the growth rate of the active layer is higher than any of the growth rates of the upper cladding layer of lGaN.