KR20010096329A - Preparation of Thick Film of Gallium Nitride by lower-layer Substrate-Sublimation and Reaction Apparatus Thereof - Google Patents

Abstract

PURPOSE: A method for manufacturing a GaN thick film using a lower substrate-sublimation method and a reaction device are provided to obtain an improved GaN thick film by using a lower substrate-sublimation method. CONSTITUTION: A crystal bath(4) is located in an inside of an electric furnace(3). A reaction vessel(5) is located in an inside of the crystal bath(4). The reaction vessel(5) is manufactured by a graphite coated with a silicon carbide. A substrate(2) is located at a lower portion of the reaction vessel(5). GaN powder(1) is located on an upper portion of the reaction vessel(5). A GaN substrate(2) is manufactured by using a lower substrate-sublimation method. Impurities are removed from a reaction device by using a vacuum pump. The GaN powder(1) is sublimated under a temperature of 1000 to 1100 degrees centigrade. The GaN substrate(2) is formed by performing the sublimation process during 1 to 4 hours.

Description

Preparation of Thick Film of Gallium Nitride by lower-layer Substrate-Sublimation and Reaction Apparatus Thereof}

The present invention relates to a method for producing a thick film of GaN and a reaction apparatus thereof, and more particularly, to obtain a single source of GaN powder at low temperature, thereby improving sublimation efficiency, and having a good crystallinity and surface structure. A method for producing a crystal and an apparatus used therefor.

GaN-based III-V nitride technology is advancing faster than experts predict, and the market for laser diodes, light emitting diodes (LEDs), outdoor billboards and digital video discs (DVDs) are emerging as next-generation video devices. It was recognized as a material technology that was the hottest development competition in 1999. For example, the diffusion of GaN's blue LEDs is expanding day by day, and downtown Seoul alone has been installed in dozens of full-color, high-resolution outdoor billboards. Recently, Nichia and Matsusida of Japan announced the next generation of DVDs that can store 15-Gbytes on a single CD using GaN LD.

In Korea, the development of III-V nitride began in 1996, and the competition for various developments is very intense. However, the selection of an appropriate substrate is very important because high quality crystal growth is required for commercialization of not only laser diodes but also electrical devices. It is now the most widely used as a substrate for GaN, but use a sapphire GaN or AlN buffer layer due to a difference (about 25%) of the difference (approximately 15%) and the thermal expansion coefficient of the larger lattice constant between GaN and the quality is also 10 ⁸ -10 Defects on the order of ⁹ cm ⁻² are generated and the reliability as electrical and optical elements is very weak. In the case of SiC substrates, not only is it expensive, but surface treatment is a problem. In addition, various materials such as spinnel, ZnO, LiGaO ₂ and LiAlO ₂ are considered as substrates for GaN.

The best way to solve the above problem is to use a GaN substrate in lattice match with GaN. This is because it is possible to deposit high quality GaN thin films by reducing defects, which are the most problematic problem in GaN deposition. Recently, Japan's Sakai and others have grown GaN single crystal using the upper substrate-sublimation method. Until now, an upper substrate-sublimation method has been used as a method for thick film growth of GaN. Here, the upper substrate-sublimation method is a case where GaN sublimation and crystal growth are performed on the bottom of the substrate by placing a source of GaN on the lower layer and placing the substrate to be sublimated on the upper layer. However, in the case of the upper substrate sublimation method, there are still difficulties in technical applications due to low sublimation efficiency, cracks and defects.

The present invention is to solve the problems as described above, by producing a GaN thick film as a technique of the developed lower substrate-sublimation method, through which the method of manufacturing a GaN thick film with improved crystallinity, surface structure and sublimation efficiency and An object of the present invention is to provide a reactor.

1 is a cross-sectional view showing a reaction apparatus for GaN thick film growth,

2, 3 and 4 are scanning microscopes, PL and X-ray diffraction photographs of the thick film crystals obtained in Example 1, respectively.

5 is a scanning micrograph of a thick film crystal obtained in Comparative Example 1. FIG.

* Explanation of symbols for the main parts of the drawings *

1: GaN powder, 2: substrate

3: electric furnace, 4: crystal tube

5: reaction vessel, 5-1: jaw

The manufacturing method of the present invention is characterized by preparing a single source of GaN, forming a stable powder by heat treatment, and then producing a thick film of GaN by a lower substrate-sublimation method.

Hereinafter, the present invention will be described in detail.

The manufacturing method of the present invention is a technique of the lower layer substrate-sublimation method in which a GaN thick film growth is placed in a silicon-carbide coated graphite reaction tube in a quartz tube and then a substrate is placed at a distance of 5 to 20 mm at the bottom thereof. Through this, it can be produced a GaN thick film of 20 ~ 1000 ?? m thick and 1cm × 1cm ~ 1 ″ × 1 ″ size.

The reactor of the present invention is configured as shown in FIG.

1 is a cross-sectional view of the reactor of the present invention, the quartz tube 4 is located inside the electric furnace 3, and the reaction vessel 5 is located inside the quartz tube. The reaction vessel 5 is made of graphite coated with silicon carbide. The substrate 2 is positioned below the reaction vessel 5, and the GaN powder 1 is positioned above.

As a problem of conventional GaN substrate fabrication by the upper substrate-sublimation method, vacancy occurs for gallium and nitrogen atoms, crack formation due to decomposition of GaN, and inefficiency of sublimation due to low gallium and nitrogen atom binding rates. Can be pointed out.

In the manufacturing method of the present invention, a GaN substrate is manufactured by a lower substrate-sublimation method using a reaction apparatus as shown in FIG.

Before starting the reaction, it is preferable to use a vacuum pump to remove impurities in the apparatus by applying a vacuum until the atmospheric pressure in the apparatus reaches a vacuum degree of about 1 × 10 ⁻⁴ torr. After removing the impurities, the GaN powder 1 is placed on the jaw 5-1 formed on the upper portion of the reaction vessel 5, and the substrate 2 is positioned below the reaction vessel 5. The suitable spacing between the GaN powder and the substrate 2 is 5-20 mm. For this reason, it is difficult to supplement the bond between the gallium atom and the nitrogen atom by ammonia gas because of the short distance in the case of less than the above range, and the reach of GaN molecules due to the long distance is insufficient when the above range is exceeded. There is a problem.

Suitable sublimation temperature of GaN powder is 1000-1100 ° C. If it is less than the above range, the sublimation efficiency of GaN is low, and if it exceeds the above range, gallium and nitrogen are decomposed to cause difficulty in growing GaN crystals. In order to prevent such decomposition, it is preferable to supply ammonia and nitrogen in the reaction apparatus at a ratio of 4: 1 to 1: 1 using a gas inhaler.

Sublimation at this temperature for 1 to 4 hours yields a GaN thick film having a thickness of 20 to 1000 µm. After the temperature in the reactor is lowered to room temperature and subjected to heat treatment for about 1 hour at 800 ℃ to obtain a crystal-grown GaN substrate. The obtained crystal grown GaN is surface treated using a laser and washed.

An embodiment of the present invention is as follows.

<Example>

The substrate was cleaned for single crystal thick film growth by the sublimation method. In the cleaning process, the substrate samples were prepared after ultrasonic cleaning in trichloroethylene, acetone, and methanol for 3 minutes each. Sublimation of GaN was attempted through the design device as shown in FIG. 1. In other words, an underlayer method of subliming GaN onto a substrate using a single source of GaN powder has been used. At this time, the distance between the substrate and the GaN powder was 5 mm. Meanwhile, a vacuum pump was used to remove impurities in the reaction tube during sublimation to maintain a vacuum degree of about 1 × 10 ⁻⁴ torr. After removing impurities, sublimation was performed for 2 hours at 1080 degrees Celsius.

In particular, in order to prevent the decomposition of gallium and nitrogen, ammonia and nitrogen gas at atmospheric pressure were injected through a gas inhaler at a ratio of 1: 1. After the desired crystal growth has taken place, it is heat-treated at 800 degrees Celsius and then the GaN substrate is taken out of the reaction tube. The product is taken out and then evaluated by SEM, PL, XRD.

Examples of evaluations are shown in FIGS. 2, 3 and 4. The GaN substrate was 20 mm thick. The diagram of FIG. 2 shows that the GaN crystals grew along the substrate surface as an hcp structure, and in FIG. 3, the graph relates to the light efficiency of GaN coming from near the UV. 4 shows that the GaN crystal was well grown in the substrate direction (0001).

Comparative Example

The same procedure as in Example 1 was performed except that the upper substrate method was used instead of the lower substrate method. As can be seen in FIG. 5, the crystal size was further reduced at this time, and the uniformity of the surface structure was weakened.

As can be seen from the above examples, the present invention not only improved the sublimation efficiency of the thick film growth of GaN by the sublimation method using the underlayer substrate method, but also induced the improvement of the surface structure and crystallinity. The obtained substrate has a large area, which can reduce production cost, and exhibits superior crystallinity and surface structure as compared with a substrate using a conventional upper substrate method.

Claims (5)

The crystal tube 4 is located inside the furnace 3, the reaction vessel 5 is positioned inside the quartz tube 4, and the reaction vessel 5 has a GaN powder loading jaw 5-1 formed thereon. Reactor for producing GaN thick film substrate, characterized in that. The reactor according to claim 1, wherein the reaction vessel (5) is made of silicon carbide coated graphite material. After placing the GaN powder on the upper portion, the substrate on the lower side, the reaction proceeds for 1 to 4 hours at a temperature of 1000-1100 ℃ to form a thick film and heat treatment after the GaN thick film substrate characterized in that the heat treatment. The method of manufacturing a GaN thick film substrate according to claim 3, wherein ammonia and nitrogen are supplied at a ratio of 4: 1 to 1: 1 using a gas injector while the reaction is in progress. The method of manufacturing a GaN thick film substrate according to claim 3, wherein the distance between the GaN powder and the substrate is 5-20 mm.