JPH11243229A - Semiconductor light-emitting element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the growth of a GaN layer without using a high-cost base substrate and by lowering a substrate temperature, by a method wherein the GaN layer is formed on a glass substrate or a silicon substrate by an ECR-MBE method. SOLUTION: First, a glass substrate 21 is placed on a substrate insertion rod 18 of an ECR-MBE device 1. Prebaking is performed in a substrate exchange chamber 4 for 30 minutes at a substrate temperature of 500 deg.C and moisture and adsorbed gas adhering on the substrate 21 are removed. After that, the substrate 21 is carried in a growth chamber 3. After the substrate 21 is carried in the chamber 3, a thermal cleaning of 700 deg.C is performed on the substrate 21 for 30 minutes to obtain the clean surface of a ZnO buffer layer 22. Then, formation of a low-temperature growth GaN buffer layer is conducted for 20 minutes on a prescribed film-forming condition to obtain a buffer layer 23 of a film thickness of 20 μm. This layer 23 is an amorphous layer and has an effect to raise the crystallizability of a single crystal GaN film 24, which is properly grown afterwards.

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 using III-V GaN material and InGaN material, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a light emitting diode (LED) using GaN having a wide forbidden band has been known as a semiconductor light emitting device that emits light in a blue region. In the case of using GaN, it is extremely difficult to form a bulk crystal thereof, so that selection of an optimum substrate and a method of growing a crystal are important issues. Regarding this point, a method of growing a GaN layer by a metalorganic compound vapor deposition method (hereinafter referred to as MOCVD method) using a single crystal sapphire substrate as a base substrate for growing the GaN layer has been attempted. However, since the sapphire substrate and GaN have significantly different lattice constants (specifically, the difference between the lattice constants is as large as about 16.1%), the grown GaN has a dislocation density of 108 to 10%.
A large number of crystal defects of 11 / cm 2 were generated, and it was difficult to grow a high-quality GaN layer having excellent crystallinity.

On the other hand, recently, a polycrystalline or amorphous AlN layer is interposed between a sapphire substrate and a GaN layer as a buffer layer to reduce the difference in lattice constant between the underlying substrate and the GaN layer. A method of growing a GaN layer having excellent crystallinity on a single-crystal sapphire substrate has been proposed. Furthermore, it has been found that by using a ZnO layer as a buffer layer, a GaN layer can be grown on an amorphous substrate such as quartz glass in addition to a single-crystal sapphire substrate. (For example, see
139361).

Incidentally, even in these prior arts in which a buffer layer of AlN, ZnO or the like is interposed between an underlying substrate and a GaN layer, MOCVD is mainly used as a method of forming the GaN layer. ing.

[0005]

However, the conventional semiconductor light emitting device has the following problems.

First, a single crystal sapphire substrate conventionally used as a base substrate for a GaN layer has a high manufacturing cost because the substrate is expensive.

In any of the above-mentioned prior arts, the GaN layer is formed by the MOCVD method.
In the case of using the CVD method, the substrate is heated to 1000 ° C. to 1
It is necessary to heat to a high temperature of about 200 ° C. Due to this high temperature, the following problems are caused. First, G
A substrate that can be used as a base substrate for growing an aN layer is
The substrate is limited to a substrate having high heat resistance that can withstand the high temperature described above. Second, since the substrate temperature during the formation of the GaN layer is high, the substrate temperature is strongly affected by the difference in the coefficient of thermal expansion between the underlying substrate and GaN. Specifically, for example, when a GaN layer is formed on a single-crystal sapphire substrate, the single-crystal sapphire substrate, the GaN , The single crystal sapphire substrate shrinks significantly compared to the GaN layer. For this reason, distortion, cracks, and crystal defects often occur in the GaN layer, and as a result, it is difficult to obtain an element having good crystal quality and sufficient luminous efficiency.

Accordingly, the present invention has been made to solve the above technical problems, and can grow a GaN layer without using an expensive undersubstrate.
An object of the present invention is to provide a semiconductor light emitting device in which a GaN layer is grown at a lower temperature and is less affected by a difference in thermal expansion coefficient between a substrate and GaN, and a method for manufacturing the same.

[0009]

According to a first aspect of the present invention, there is provided a semiconductor light emitting device, comprising: a glass substrate or a silicon substrate;
A GaN layer is formed by the E method. In forming the GaN layer, it is preferable to interpose ZnO having a lattice constant relatively close to that of GaN and easily formed on a glass substrate or a silicon substrate as a buffer layer from the viewpoint of improving the crystallinity of the GaN layer. GaN with better crystallinity
In order to form a layer, it is preferable to form a GaN layer on a low-temperature-grown GaN buffer layer formed at a low temperature of about 400 ° C. to 500 ° C.

As described above, by forming the GaN layer by the ECR-MBE method, the substrate temperature at the time of forming the GaN layer can be reduced, so that an inexpensive glass substrate or silicon substrate can be used as the base substrate. Become. In particular, when a glass substrate is used as the base substrate, since the difference in thermal expansion coefficient from GaN is small, the above-mentioned adverse effects caused by the difference in thermal expansion coefficient can be reduced.

[0011] In the semiconductor light emitting device according to claim 6 of the present invention, an ECR is provided on a glass substrate or a silicon substrate.
-Form an InGaN layer by MBE. Also,
In forming the InGaN layer, the lattice constant is InGa
ZnO, which is relatively close to N and is easily formed on a glass substrate or a silicon substrate, can be interposed as a buffer layer.
It is preferable from the viewpoint of improving the crystallinity of the nGaN layer. In order to form an InGaN layer with better crystallinity, about 4
Low temperature growth InG formed at a low temperature of about 00 to 500 ° C
Preferably, an InGaN layer is formed on the aN buffer layer.

As described above, the InGaN layer is formed by the ECR-MB
By forming by the E method, the substrate temperature at the time of forming the InGaN layer can be lowered, so that an inexpensive glass substrate or silicon substrate can be used as the base substrate. In particular, when a glass substrate is used as the base substrate,
Since the difference in thermal expansion coefficient from nGaN is small, the above-mentioned adverse effects caused by the difference in thermal expansion coefficient can be mitigated.

[0013]

Embodiments of the present invention will be described below.

First, FIG. 1 shows a schematic view of an ECR-MBE apparatus used for manufacturing the semiconductor light emitting device of the present invention. Book E
As shown in FIG. 1, the CR-MBE apparatus 1 includes three chambers, a plasma generation chamber 2, a growth chamber 3, and a substrate exchange chamber 4.

In the plasma generation chamber 2, the nitrogen gas whose flow rate is controlled by a mass flow controller (not shown) is 2.4.
By applying a microwave of 5 GHz and a magnetic field of 875 G, an electron cyclotron resonance (ECR) phenomenon is caused to generate plasma. The generated nitrogen gas plasma flows from the plasma generation chamber 2 to the growth chamber 3 by the divergent magnetic field.

First, a substrate holder 12 for holding a substrate 11 is provided in the growth chamber 3. Substrate holder 12
Is provided with a heater for heating the substrate 11. The growth chamber 3 is provided with voltage applying means 13 for applying a DC bias to the positive and negative directions between the vacuum chamber constituting the growth chamber 3 and the substrate holder 12. Thereby, the ionized raw material can be efficiently fixed on the substrate 11, and at the same time, the substrate 1
To reduce ion irradiation damage by suppressing collision with
The quality of the crystal film grown on the substrate 11 can be improved. Further, a Knudsen cell 14 for supplying metal Ga as a Ga source and a Knudsen cell 15 for supplying metal In as an In source are provided. These Ga and In materials react with the plasma-like nitrogen gas flowing from the plasma generation chamber 2 to form a GaN film or an InGaN film on the substrate 11. At this time, since the nitrogen gas is supplied in an ECR plasma state having high energy, the substrate temperature can be reduced by the amount of the excitation energy. An RHEED electron gun 16 and a screen 17 are provided as an apparatus for evaluating the state of film formation on the substrate 11.

The substrate exchange chamber 4 is provided with a substrate carrying rod 18 for carrying the substrate 11 into the growth chamber 3. Further, a heater for preheating the substrate is also attached to the substrate carrying rod 18. Thereby, film formation on the substrate can be performed continuously, and the substrate 11 can be formed in the growth chamber 3.
Can be reduced in the amount of outgassed gas generated when heating is performed.

The growth chamber 3 and the substrate exchange chamber 4 are provided with independent exhaust systems (for example, composed of a turbo molecular pump and an oil rotary pump (not shown)), and are separated from each other by the gate valve 19 except when the substrate is transported. . Thereby, the growth chamber 3 can always be kept in a state of high vacuum with few residual impurity molecules.

[First Embodiment, FIGS. 2 to 4] In this embodiment, a semiconductor light emitting element 20 having the film structure shown in FIG. 2 is formed on a substrate by using the ECR-MBE apparatus 1 described above. . Hereinafter, the substrate and raw materials used for the film formation of this example and the film formation procedure will be described.

The substrate used in this embodiment is an inexpensive borosilicate glass substrate 21 (hereinafter simply referred to as a glass substrate).
Is used. On this glass substrate 21, a ZnO buffer layer 22 having a thickness of about 3 μm is formed in advance by an RF magnetron sputtering method or the like. The ZnO buffer layer 22 is a c-axis oriented polycrystalline film. Further, as a group III raw material used for growing a GaN film, a purity of 8N (99.99) is used.
9999%) of metal Ga, and nitrogen gas having a purity of 5N is used as a group V raw material.

Next, a film forming procedure will be described. First, the glass substrate 21 is placed on the substrate carrying rod 18 of the ECR-MBE apparatus 1. Then, at a substrate temperature of 500 ° C. in the substrate exchange chamber 4,
Pre-bake for 0 minutes is performed to remove moisture and adsorbed gas adhering to the substrate 21. Thereafter, the glass substrate 21 is placed in the growth chamber 3.
Carry in. After carrying the glass substrate 21 into the growth chamber 3, thermal cleaning at 700 ° C. is performed for 30 minutes.
A cleaned surface of the ZnO buffer layer 22 is obtained. Next, a low-temperature-grown GaN buffer layer is formed for 20 minutes under the film forming conditions shown in Table 1 below to obtain a buffer layer 23 having a thickness of about 20 nm. This low-temperature-grown GaN buffer layer 23 is amorphous, and has an effect of improving the crystallinity of the single-crystal GaN film 24 to be finally grown later. The degree of vacuum in the growth chamber 3 is maintained at about 10-7 torr.

[0022]

[Table 1]

After forming the low-temperature-grown GaN buffer layer 23, the GaN film 24 is continuously formed under the film forming conditions shown in Table 2 below.
For 120 minutes. The degree of vacuum in the growth chamber 3 is similarly maintained at about 10-7 torr.

[0024]

[Table 2]

The semiconductor light emitting device 20 having the film structure shown in FIG. 2 is obtained through the above film forming procedure. Here, the time chart of the GaN film forming procedure described above is shown in FIG.
Shown in As is clear from FIG. 3, in the series of GaN film forming processes of the present embodiment, the substrate temperature was constantly set to 700.
It is possible to maintain the temperature below 200 ° C. (Note that, although not described, the process of forming the ZnO buffer layer 22 on the glass substrate 21 also requires the substrate temperature of about 200 ° C. when the RF magnetron sputtering method is used. The film can be formed with).
As a result, a material having a low melting point and softening point can be used as the base substrate, and a wide range of substrate materials can be selected. For example, the melting point of borosilicate glass, which has been difficult to use in the past, is low (specifically, the softening point of borosilicate glass is 775 ° C), but an inexpensive substrate material can be used. Becomes

Finally, the Ga film obtained through the above film forming procedure is obtained.
The optical characteristics of the N film will be discussed. As a method for evaluating optical characteristics, measurement of a photoluminescence spectrum using a He-Cd laser as an excitation light source is performed at a temperature of 77K. FIG. 4 shows the measurement results. 4, the horizontal axis represents the emission wavelength λ, and the vertical axis represents the light intensity (unit: au).
As can be seen from this figure, in the GaN film obtained in the present example, an emission spectrum mainly near the band edge (360 nm) was confirmed.

[Second Embodiment, FIGS. 5 to 6] In this embodiment, the semiconductor light emitting element 30 having the film structure shown in FIG. 5 is formed on a substrate by using the above-described ECR-MBE apparatus 1. . Hereinafter, the substrate and raw materials used for the film formation of this example and the film formation procedure will be described.

In this embodiment, a group III raw material used for growing an InGaN film has a purity of 8N (99.99999).
9%) of metal Ga and metal In of the same purity of 8N. Other materials and substrates are the same as in the first embodiment.

As for the film forming procedure, low-temperature growth InGaN
The conditions for forming the buffer layer 33 and the conditions for forming the InGaN layer 34 are set as shown in Table 3 below. Other points are the same as in the first embodiment, and the description thereof will be omitted.

[0030]

[Table 3]

The semiconductor light emitting device 30 having the film structure shown in FIG. 5 is obtained through the above film forming procedure. In the process of forming a series of InGaN films according to the present embodiment, the substrate temperature can be constantly maintained at 700 ° C. or lower.

FIG. 6 shows the optical characteristics of the InGaN film obtained through the above film forming procedure. The same evaluation method as that of the first embodiment was used. As can be seen from this figure, in the InGaN film obtained in this example, an emission spectrum was mainly observed near the band edge (380 nm).

[Other Embodiments] The present invention is not limited to the film forming conditions shown in the above embodiments, but may be variously modified within the scope of the invention. For example, in each of the above-described embodiments, a borosilicate glass substrate is used as a base substrate. However, the present invention is not limited to this, and a silicon substrate can also be used as an inexpensive base substrate. Since a silicon substrate has a higher melting point and softening point temperature than a glass substrate (specifically, about 1400 ° C.), it is possible to form a film at a higher substrate temperature. There is an advantage that a good GaN layer and an InGaN layer can be easily obtained (generally, the higher the film formation temperature, the better the crystallinity of the film formed). However, even in this case, the substrate temperature at the time of film formation needs to be kept below 900 ° C. This is because the substrate temperature is 900 ° C
This is because ZnO, which is the buffer layer, starts to sublime from the vicinity of over. As the sublimation of ZnO proceeds, its function as a buffer layer is reduced, so that the film quality (crystallinity) of the GaN layer formed thereon is deteriorated. in addition,
The sublimated active O and Zn combine with the film forming material, and there is a possibility that a large amount of impurities are taken into the GaN layer. From these viewpoints, it is necessary to keep the substrate temperature during film formation at less than 900 ° C. When a silicon substrate is used as the base substrate, another advantage is that another semiconductor device can be integrated and formed on the same substrate as the substrate on which the GaN layer is formed.

Further, it is also possible to form a semiconductor light emitting device which emits light in the blue region by mixing Al with the film forming material of each of the above embodiments.

[0035]

As is clear from the above description, according to the semiconductor light emitting device of the present invention, the following excellent effects can be obtained. That is, since the ECR-MBE method is used to form the GaN layer or the InGaN layer, it becomes possible to supply a nitrogen gas as a raw material into plasma by ECR and to supply the same, and it is possible to lower the substrate temperature by the amount of the excitation energy.

As described above, by lowering the substrate temperature during film formation, a material having a low melting point can be used as the base substrate, and a wide range of substrate materials can be selected. For example, inexpensive borosilicate glass, which was conventionally difficult to use, can be used as a substrate material, and the manufacturing cost of a semiconductor light emitting device can be reduced.

Further, by lowering the substrate temperature, it is possible to suppress an adverse effect due to a difference in thermal expansion coefficient between the underlying substrate and GaN. The coefficient of thermal expansion between GaN and the glass substrate is relatively close (specifically, the difference between the coefficient of thermal expansion between GaN and glass is about 10%. Note that the coefficient of thermal expansion between GaN and the sapphire substrate (The difference is about 34%.) Further, since the grown GaN film is free from cracks, a GaN film having good crystal quality and sufficient luminous efficiency can be obtained without cracking.

[Brief description of the drawings]

FIG. 1 is an EC used for manufacturing a semiconductor light emitting device of the present invention.
It is a schematic diagram of an R-MBE apparatus.

FIG. 2 is a sectional view showing a film structure of the semiconductor light emitting device of the first embodiment.

FIG. 3 shows a structure of a semiconductor light emitting device of the first embodiment, G
FIG. 3 is a time chart illustrating a procedure for forming an aN film.

FIG. 4 is a measurement diagram showing a result of photoluminescence spectrum measurement of the semiconductor light emitting device of the first embodiment.

FIG. 5 is a sectional view showing a film structure of a semiconductor light emitting device of a second embodiment.

FIG. 6 is a measurement diagram showing a result of a photoluminescence spectrum measurement of the semiconductor light emitting device of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... ECR-MBE apparatus 2 ... Plasma generation chamber 3 ... Growth chamber 4 ... Substrate exchange chamber 11 ... Substrate 12 ... Substrate holder 13 ... Voltage applying means 14 ... Knudsen cell (Ga) 15 ··· Knudsen cell (In) 16 ··· RHEED electron gun 17 ··· Screen 18 ··· Substrate carrying rod 19 ··· Gate valve 20 and 30 ··· Semiconductor light emitting element 21 31 ... borosilicate glass substrate 22, 32 ... ZnO buffer layer 23 ... low-temperature growth GaN buffer layer 24 ... GaN layer 33 ... low-temperature growth InGaN buffer layer 34 ... InGaN layer

Claims (10)

[Claims] 1. A method according to claim 1, wherein a glass substrate or a silicon substrate is provided with E
A semiconductor light emitting device, wherein a GaN layer is formed by a CR-MBE method. 2. The semiconductor light emitting device according to claim 1, wherein a ZnO buffer layer is formed on a surface of said glass substrate or silicon substrate. 3. The semiconductor light emitting device according to claim 1, wherein the GaN layer is formed on a low-temperature-grown GaN buffer layer. 4. The method according to claim 1, wherein the glass substrate or the silicon substrate has
A method for manufacturing a semiconductor light emitting device, wherein a GaN layer is formed by a CR-MBE method. 5. A step of preparing a glass substrate or a silicon substrate, and forming Zn on a surface of the glass substrate or the silicon substrate.
Laminating an O buffer layer, laminating a low-temperature grown GaN buffer layer on the ZnO buffer layer, and forming a GaN layer on the low-temperature grown GaN buffer layer by ECR-MBE.
And laminating the layers. 6. A method according to claim 1, wherein the glass substrate or the silicon substrate has
A semiconductor light emitting device, wherein an InGaN layer is formed by a CR-MBE method. 7. The semiconductor light emitting device according to claim 6, wherein a ZnO buffer layer is formed on a surface of said glass substrate or silicon substrate. 8. The InGaN layer is formed by low-temperature grown InGa.
8. The semiconductor light emitting device according to claim 6, wherein the semiconductor light emitting device is formed on an N buffer layer. 9. A glass substrate or a silicon substrate, wherein E
A method for manufacturing a semiconductor light emitting device, wherein an InGaN layer is formed by a CR-MBE method. 10. A step of preparing a glass substrate or a silicon substrate, and forming Z on the surface of the glass substrate or the silicon substrate.
laminating an nO buffer layer, laminating a low-temperature grown InGaN buffer layer on the ZnO buffer layer, and laminating an InGaN layer on the low-temperature grown InGaN buffer layer by ECR-MBE. Of manufacturing a semiconductor light emitting device.