Fabricating Gallium Nitride Epilayer on Zinc Oxide Buffer Layer via Pulsed Laser Deposition System and Opto-electric Properties Analysis

• Main Authors: Chun-Wei Ku, 古竣偉
• Other Authors: Ching-Fuh Lin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/h2y3hz

碩士 === 國立臺灣大學 === 光電工程學研究所 === 101 === The study of this thesis is to investigate the hydrothermal method for growing high-quality zinc oxide thin film and the homemade pulsed laser deposition system for fabricating high-quality gallium nitride thin film on zinc oxide buffer layer. First, we introduce to obtain high-quality ZnO thin film via hydrothermal method. After that, we use homemade PLD to fabricate high-quality GaN thin film on ZnO buffer layer, and then the effect of nitrogen pressure on properties of GaN thin film is also investigated. In the study of growing high-quality ZnO thin film, the ZnO thin film was successfully fabricated on the p-type GaN epilayer via the hydrothermal method. We successfully used chemical kinetics to simulate the relationship of the growth concentration and the growth time, thus determining the optimal conditions to fabricate the ZnO thin film on a p-type GaN epilayer. Subsequently, we used AFM, EDS, XRD, and Hall measurements to analyze the characteristics of the ZnO thin film. The roughness of the ZnO thin film is determined by AFM to be about 5.46 nm, where there is no other impurity detected in the EDS spectrum. Besides, under the growth temperature of 90°C and the growth concentration of 100mM for 6 hours, the XRD FWHM of ZnO (0001) shows =0.1682°, which is neck and neck with that fabricated by PLD. This means that it is possible to fabricate good quality ZnO thin film via a low cost hydrothermal method and it can be applied in many fields. We have further fabricated n-ZnO layer onto p-GaN layer to fabricate hetero-junction LEDs and successfully achieved a rectifying I-V curve and light emission from current injection. The EL emission of the LED is dominated in the ZnO layer. All results show that the ZnO thin film fabricated by the low-cost hydrothermal method has good potential for possible applications in the industry of light-emitting diodes and take the place of GaN for the material of emitting layer. Next, we use homemade pulsed laser deposition system to epitaxy high-quality gallium nitride thin film on zinc oxide buffer layer. During the deposition process, the high energy plume collides or scatters with nitrogen in atmosphere. This phenomenon greatly affected the crystalline of GaN thin film. The experimental data shows that the properties of GaN thin film fabricate under deposition condition substrate heating temperature 900 oC, laser energy 600mJ/pulsed, 7 Hz laser repetition frequency, and operating nitrogen pressure at 1x10-2 torr are very good. The UV-visible spectrum shows that average transmittance in the visible range is 87 % , and the EDS spectrum reveals that the element ratio of Ga and N is approach to 1:1. The XRD FWHM of the GaN (0002) thin film shows =0.293°, which is neck and neck with that deposited by MOCVD. Furthermore, the surface roughness of the GaN thin film is only 1.6312 nm. It means that this high-quality GaN thin film is also fairly flat.