  |
The third-generation semiconductor material has a large band gap, and has the advantages of high breakdown electric field, high thermal conductivity, high electron saturation rate, and strong anti-radiation ability. Therefore, it is suitable for making high-voltage, high-frequency, high-current devices, and can also reduce The power consumption of the device.
Development history of gallium nitride materials and MOCVD preparation process Gallium nitride has the characteristics of large forbidden band width, high breakdown voltage, large thermal conductivity, high saturated electron drift speed and strong radiation resistance. It is the material with the highest electro-optical and photoelectric conversion efficiency theoretically so far.
The epitaxial growth methods of gallium nitride mainly include metal organic chemical vapor deposition MOCVD, hydride vapor phase epitaxy HVPE, and molecular beam epitaxy MBE. The basic chemical principle of MOCVD growth of gallium nitride is to pass Ga(CH)3 in vapor state and gaseous NH3 in the reaction chamber, a series of reactions occur in a high temperature environment, and finally a gallium nitride epitaxial layer is formed on the surface of the substrate:
MOCVD technology was first proposed by Manasevit in 1968. With the improvement of raw material purity and process improvement, this method has gradually become the second generation semiconductor material represented by gallium arsenide and phosphorus indium, and the third-generation semiconductor represented by gallium nitride. The main growth process of the material. In 1993, Nakamura and others of Nichia Chemical used the MOCVD method to achieve high-quality management of the preparation of InGaN indium gallium nitride epitaxial layers, which shows the importance of MOCVD in the third generation of semiconductor materials.
The advantage of MOCVD is that the reactants enter the reaction chamber in gaseous form, and the thickness, composition and carrier density of the epitaxial material can be controlled by precise control of various gas flows; the second is that the gas flow in the reaction chamber is fast, which can be changed The gas is used to obtain a steep heterojunction interface; the third is to obtain less impurities and high crystal quality; the fourth is that the equipment is relatively simple, which is conducive to large-scale industrial production.
MOCVD is becoming more and more important in the preparation of three-group compound semiconductor materials. In terms of equipment supply, in addition to Aixtron of Germany and VECCO of the United States, China Micro Corporation has also achieved major breakthroughs, and MOCVD has achieved domestic substitution. Hydride gas phase epitaxy process and its disadvantages In fact, the initial growth method of gallium nitride was hydride vapor phase epitaxy HVPE, which was originally used by Maruska et al. to make gallium nitride epitaxial layers. The HVPE reaction is usually carried out in a hot quartz reactor at atmospheric pressure. The basic chemical reaction is that gaseous hydrogen chloride reacts with metallic gallium in a low temperature environment to produce gaseous gallium chloride, which then reacts with gaseous ammonia in a high temperature environment. The reaction produces a gallium nitride film, and the by-products of the reaction hydrogen chloride and hydrogen can be recovered in gaseous form.
The preparation of gallium nitride by HVPE requires a two-step chemical reaction: a low-temperature reaction and a high-temperature reaction. Therefore, the HVPE reactor needs to divide the reaction chamber into a low-temperature zone and a high-temperature zone. At the same time, many parameters need to be adjusted in this process to achieve the gallium nitride film Controllable and deposition.
In the 1970s and 1980s, the HVPE method was widely used for the growth of gallium nitride, but many defects of this method were found in the application: the prepared gallium nitride has a large number of crystal defects, and the crystal quality is poor, mainly due to spatial parasitic reactions. Because HVPE operates under normal pressure, a large number of parasitic gallium nitride particles will be deposited on the outlet of gallium chloride gas in the reactor, the growth surface and the surface of the quartz glass tube wall, and the parasitic gallium nitride will not only consume gallium chloride This results in a decrease in the growth rate, damage to the gallium chloride pipeline, and crystal defects.
In addition, this method cannot control the doping well, and it is difficult to achieve P-type doping, so it was once abandoned. However, after the 1990s, HVPE was re-emphasized by the industry because of its relatively simple equipment. In addition, technological advances have made HVPE grow at a faster rate of gallium nitride, and it is easy to produce large-area films with better film uniformity.
In addition to MOCVD, MBE molecular beam epitaxy has also become an important growth method for semiconductor materials such as gallium nitride. MBE is an epitaxial growth method for growing high-quality crystal films on the surface of a substrate, but it needs to be performed in a high vacuum or even an ultra-high vacuum environment.
The advantages of MBE are: Although the MBE growth rate is usually no more than 1 micron/hour, which is equivalent to growing a single atomic layer per second or longer, it is easy to achieve precise control of film thickness, structure and composition, and it is easy to achieve steepness. The heterostructure and quantum structure of the interface; the second is the low epitaxial growth temperature, which reduces the lattice defects introduced by the different thermal expansion coefficients at the interface; the third is that MBE is a physical deposition process compared to the chemical processes of HVPE and MOCVD , So do not consider the impurity pollution caused by chemical reactions.
|
All contents are reproduced in all forms without written permission.© Copyright 2017 Wuxi Zhuohai Technology. All rights reserved. | 苏ICP备10225498号-2
We recommend that you use IE8.0 and above browser to visit this site.