Growths of III-V Nitride Semiconductors with the Techniques of Metalorganic Vapor Phase Deposition and Molecular Beam Epitaxy

• Main Authors: Jeng-Jie Huang, 黃政傑
• Other Authors: 楊志忠
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/43946718946711784153

博士 === 國立臺灣大學 === 光電工程學研究所 === 99 === In this dissertation, first pit-free a-plane GaN (11-20) growth on r-plane sapphire (1-102) substrate with metalorganic chemical vapor deposition (MOCVD) is reported. We use the flow-rate modulation epitaxy (FME) technique to improve the crystal quality of an a-plane GaN film. With the FME technique, the width of the rocking curve in X-ray diffraction measurement is significantly reduced. Also, the surface roughness based on either atomic-force-microscopy scanning or a-step profiling is decreased. Here, the FME technique means to alternatively turn on and off the supply of Ga atoms while N atoms are continuously supplied without changing the flow rate. Under the used growth conditions, the optimized FME parameters include the on/off period at 10/10 sec. During the period of closing the flow of TMGa, the continuous supply of nitrogen can lead to the formation of stoichiometry structure under the high-Ga growth condition, which is required for the growth pit-free morphology. Also, during this period, Ga atoms can further migrate to result in a flatter surface. Therefore, the crystal quality of the a-plane GaN sample can be improved. Besides, we study the crystal quality of a-plane GaN grown on r-plane sapphire substrate based on the FME technique combined with epitaxial lateral overgrowth (ELOG). With or without epitaxial lateral overgrowth (ELOG), either c- or m-mosaic condition is significantly improved in the samples of using FME. With ELOG, the surface roughness can be reduced from 1.58 to 0.647 nm in an area of 10 x 10 square microns by using the FME technique. Based on the results of photoluminescence measurement, one can also conclude the better optical property of the FME-grown a-plane GaN thin films. Besides, it is shown that tensile strain is more relaxed in the FME samples. In addition, we grow p-GaN layer on n-ZnO templates to fabricate a heterojunction ZnO-based LED. To prevent the thermal annealing effects of high temperature growth of the top p-GaN layer, the p-GaN layer is grown with molecular beam epitaxy (MBE) instead of high temperature MOCVD growth. The current-voltage (I-V) curves of p-GaN/n-GaN diodes are used as the indicators for the successful p-type doping of a p-GaN layer. It is found that only when the Mg effusion cell temperature is as high as 430 oC, we can obtain good current rectifying results. The electroluminescence (EL) characterization of such a p-GaN/n-ZnO diode shows broad band luminance, covering violet, blue, orange-red, red and near infra-red peaks. However, the expected near band edge ultra-violet (UV) luminance of the ZnO or GaN films cannot be observed. This is due to the high band-tail absorption of the top p-GaN layer. Only those photons with lower energy can pass through the p-GaN layer and be observed.