JPS5948794B2 - Manufacturing method of gallium nitride single crystal film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a gallium nitride single crystal film free from large strains or defects.

Conventionally, gallium nitride single crystal films have been grown mainly on sapphire single crystals by chemical vapor deposition, chemical vapor deposition, or sputtering. When growing gallium nitride on a sapphire substrate, for example, on the sapphire (0001) plane, the (0001) plane of gallium nitride is parallel to the substrate surface, and the [11'20] orientation of gallium nitride is parallel to the [11'20] orientation of sapphire.
1Too] is epitaxially grown parallel to the direction. At this time, the lattice mismatch between gallium nitride and sapphire is about 13% in the sapphire [1 Too] direction, which causes large distortions and defects in the gallium nitride film, which becomes a factor in the deterioration of characteristics such as light emission of gallium nitride. There is. In order to avoid this, it is necessary to grow a gallium nitride film with a thickness of several micrometers or more, but defects due to lattice misalignment cannot be completely eliminated. In some cases, this is one of the factors that lowers the luminous efficiency. In view of the above circumstances, the inventors of the present application have conducted various experiments and research with the aim of growing a high quality gallium nitride single crystal film with few distortions and defects on a sapphire substrate, and have found that aluminum nitride can achieve this purpose. It has been found that this method is extremely effective.

That is, aluminum nitride has the same wurtzite crystal structure as gallium nitride, and the lattice mismatch is about 2%, which is extremely small compared to the 13% lattice mismatch between gallium nitride and sapphire, so it cannot be grown on aluminum nitride. It is expected that the gallium nitride produced by this process will have less distortion and defects. On the other hand, aluminum nitride and sapphire still have a large lattice mismatch of about 11%, but since aluminum is a common constituent element, a high quality aluminum nitride single crystal film can be obtained.

When making a light emitting device using gallium nitride, a method is used in which light is extracted to the outside through a sapphire substrate.
Aluminum nitride has a sufficiently larger band gap energy than gallium nitride and is transparent in the emission wavelength range of gallium nitride, so even if there is an aluminum nitride layer between sapphire and gallium nitride, light cannot be emitted from the sapphire substrate side. It does not prevent you from taking it outside. This invention was completed based on the above knowledge, and its gist is to grow an aluminum nitride single crystal film on a sapphire substrate, and then grow a gallium nitride single crystal film thereon. It is something. An important point in this method for producing a gallium nitride single crystal film is that an aluminum nitride single crystal is grown on the sapphire substrate in advance.

Aluminum nitride single-crystal films can be grown on sapphire substrates by chemical vapor deposition, in which aluminum is evaporated in an ammonia or hydrazine atmosphere, or chemical vapor deposition, in which aluminum-containing compound gas and ammonia gas are introduced into a reaction tube. It may depend on

Gallium nitride can be grown on an aluminum nitride single crystal film by either chemical vapor deposition, which evaporates gallium in an ammonium or hydrazine atmosphere, or chemical vapor deposition, which introduces a compound gas containing gallium and ammonia gas into a reaction tube. You can rely on it.

The chemical vapor deposition method will be described below with reference to illustrated embodiments.

Vacuum chamber 1 evacuated to an ultra-high vacuum of 10-8T0rr or less
Inside, there is a substrate heating heater 2 on the back or side, and a sapphire substrate 4 is arranged so that the front side of the heater 2 is blocked by a shutter 3, and an ammonia gas introduction pipe 5 is installed in the center of the front of the sapphire substrate 4. The pipe 5 is arranged with its opening facing the sapphire substrate 4, and an aluminum evaporation source 6 and a gallium evaporation source 7 are arranged on both sides of the pipe 5.

First, an aluminum molecular beam is introduced from an aluminum evaporation source 6 in a vacuum chamber 1 evacuated to an ultra-high vacuum of 10-8 T0rr or less, and a 10-
5T0rr of ammonia is simultaneously applied to the sapphire substrate 4 heated to 1000 to 1200°C to grow an aluminum nitride single crystal film. The growth rate of the film depends on the aluminum molecular beam intensity and ammonia partial pressure.
2×1015(:!l-SeC,5XlO-5T0rr
When , it is about 2λ/Sec. Next, the aluminum molecular beam is stopped, the substrate temperature is lowered to 600-700°C, the gallium molecular beam is applied from the gallium evaporation source 7, and the ammonia of 10?5 to 10-4 T0rr is applied to the aluminum nitride single crystal film from the gas introduction pipe 5. The light is simultaneously applied to the covered sapphire substrate 4 to grow a gallium nitride single crystal film.

The growth rate of the film also depends on the gallium molecular beam intensity and ammonia partial pressure, but it is 1X1015/Cd・Sec,l
When x10-4T0rr, it is approximately 2λ/Sec.

Note that in order to grow an aluminum nitride film or a gallium nitride film, it is preferable that the gas introduction pipe be oriented toward the substrate so that ammonia molecules are directly incident on the substrate.

Furthermore, when growing an aluminum nitride single crystal film, a film with a flat surface can be obtained by first injecting an aluminum molecular beam and then starting the introduction of ammonia. Furthermore, after growing the aluminum nitride single crystal film, it is necessary to grow a gallium nitride single crystal film without exposing the film to the atmosphere.

This is because when an aluminum nitride film is exposed to the atmosphere, a thin oxide layer is formed on the surface, and a high-quality gallium nitride single crystal film cannot be grown thereon. Next, we will discuss the differences in the characteristics of gallium nitride single crystal films grown directly on a sapphire substrate and those grown by this method.

FIG. 2a shows a cathode luminescence spectrum of a gallium nitride single crystal film grown directly on a sapphire substrate, and FIG. 2b shows a cathode luminescence spectrum of a gallium nitride single crystal film produced by this method. Both show similar spectral shapes and have a wavelength of 360n.
A sharp emission peak can be seen at m. However, the strength of the gallium nitride film produced by this method is about 50 times greater. In addition, as a result of measuring the electrical properties of the film by Ha'l measurement, the electron mobility of the gallium nitride film prepared by this method is 5 to 10
twice as big. Thus, it can be seen that the light emitting and electrical properties of the gallium nitride single crystal film produced by the present method are significantly improved compared to films produced by the conventional method. This invention thus enables the growth of high-quality gallium nitride single crystal films on sapphire substrates, and is expected to be used in various applications such as light emitting devices using gallium nitride. It is something.

[Brief explanation of drawings]

Figure 1 shows the principle of manufacturing gallium nitride and aluminum nitride single crystal films by chemical vapor deposition, and Figure 2 shows the cathode luminescence spectrum of gallium nitride single crystal films at 77K. FIG. 2B is a gallium nitride single-crystal film produced by the present method, and FIG. 1A is an enlarged view of FIG. In the figure, 1 is a vacuum chamber, 2 is a substrate heating heater, 3 is a shutter, 4 is a sapphire substrate, 5 is an ammonia gas introduction pipe, 6 is an aluminum evaporation source, and T is a gallium evaporation source.

Claims (1)

[Claims] 1. A method for producing a gallium nitride single crystal film, which comprises growing an aluminum nitride single crystal film on a sapphire substrate, and then growing a gallium nitride single crystal film thereon.