Effect Of Showerhead Gap Position On The Growth Of GaN Epilayer By MOCVD

Since the20th century; with the continuous progress of high-tech technology, human society has entered a stage of rapid development, and semiconductor materials has been played an irreplaceable role in this process. After years of continuous development, following the first and second generation semiconductor materials, the third generation semiconductor material becomes hot topics in the field of optoelectronic materials with its prominent advantages. Direct and wide-band-gap semiconductor material gallium nitride (GaN), as a typical representative of the third generation semiconductor materials, has significant advantages such as high temperature resistant, radiation hardened, good thermal conductivity and high luminous efficiency. It has a broad application prospects in the production of high-temperature, high-frequency, high-power optoelectronic devices, attracts a large number of researchers’ attention and achieves continuous breakthrough since the1980s. Metal organic chemical vapor deposition (MOCVD), which is a widely used application of GaN epitaxial growth technique, becomes frontier and hot topics in recent years. The researcher conducts simulation analysis on the MOCVD internal structure and airflow field in theory, makes a number of improvements to improve the quality of the epitaxial GaN films. But there is relatively few studies conducted by experiment.In this paper, GaN epilayers were grown by MOCVD systems produced by the German AIXTRON. A series of GaN epilayers were grown with different showerhead gap position using MOCVD. The properties of GaN epilayers were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and White-Light Interferometry. The effect reason of showerhead gap position on the growth rate and quality of GaN epitaxial films was analyzed. The meaningful achievements are listed as follows:1. The showerhead gap position significantly affects the growth rate of the GaN films. Measuring the thickness of the different GaN films, the result shows that, the higher showerhead gap position height, the thinner the thickness of the films. Because the growth time is the same for all samples, the thickness changes reflect changes in the growth rate. To reduce the height of the showerhead gap position, the growth rate can be improved.2. The thickness of GaN films is more uniform with the increasing in showerhead gap position. Five different points were taken from each sample, measuring the film thickness by White-Light Interferometry; the covariancshows that, the uniformity can be improved by raising showerhead gap position. 3. The roughness of GaN epitaxy films decrease with the increasing in showerhcad gap position. This conclusion obtained by AFM. However, the thickness of the sample having a larger difference, it may also affect the surface roughness, so we need for further experiments by growing the sample of the same thickness to test and verify.4. The quality of GaN films is worse with the increasing in showerhead gap position. The FWHM of the test sample by XRD shows that, the edge dislocation are the main type of dislocation of all the samples, the dislocation density is significantly increased with the increasing in showerhead gap position, a high dislocation density will reduce the performance and reliability of the GaN-based devices..