Enhanced Performances of GaN-based MOS-HEMTs by Surface Passivation and Post Oxide Annealing

• Main Authors: Wen-ChiaOu, 歐文家
• Other Authors: Wei-Chou Hsu
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/43386885006452789517

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 101 === The research is mainly investigated on the improvement of hydrogen peroxide (H2O2) Metal-Oxide-Semiconductor high electron mobility transistor by using post oxide annealing (POA). Hydrogen peroxide has a strong oxidation capability, it can oxidize the surface of AlGaN to form the surface oxide layer. After that, we use different ambiences, temperatures, time to improve the quality of oxide layer. In order to know (1) surface roughness, (2) chemical composition, (3) oxide thickness, and (4) passivation layer effect on two-dimensional electron gas concentration (2DEG) of oxide layer, the (1) Transmission Electron Microscopy (TEM) (2) X-ray Thin-film Diffraction (XRD) (3) Electron Spectroscopy for Chemical Analysis (ESCA) (4) Atomic Force Microscopy (AFM), and (5) Hall Measurement were required to use in the research. From TEM, we observe that the thickness of oxide layer which with post-oxide annealing would reduce. The oxide thickness of H2O2 treatment, POA with O2 400°C 10minutes, and N2 400°C 20minutes are 13.33 nm, 11.11 nm, 9.51 nm, respectively. From the XRD analysis, there are crystallization at the POA with O2 400°C 15 minutes, and N2 400°C 25 minutes. From ESCA, the results of the semi-quantitative analysis show the oxide layer is aluminum oxide. The observation of AFM compare without H2O2 treatment with H2O2 treatment 7 minutes 30seconds, POA with O2 400°C 10 minutes, and N2 400°C 20 minutes. Their surface roughnesses were 1.90 nm, 1.53 nm, 0.95 nm, and 0.90 nm, respectively. The Hall measurement was compared with H2O2 treatment 7 minutes 30seconds, POA with O2 and N2 ambiences, the sheet concentration was slightly reduced and the electron mobility would improve. In addition, the reduced oxide layer traps were confirmed by utilizing the hysteresis and interface state density. After material analysis, the POA was applied to the fabrication of high electron mobility transistors. First, compared the different gases, temperatures, and time, we found that there were the optimal characteristics when POA with O2 400°C 10 minutes, and N2 400°C 20 minutes. Hence, the following texts will demonstrate comparisons of DC and RF characteristics of devices by using without H2O2 treatment, with H2O2 treatment, POA with O2 400°C 10 minutes, and N2 400°C 20 minutes. During the temperature–dependent characteristics measurement, the devices with POA have better thermal stability were observed. In order to know the condition of devices operated under high frequency, microwave characteristics measurement is required. We noticed that cutoff frequency, maximum oscillation frequency, and linearity would be improved. Power characteristics demonstrated the device characteristics at 2.4GHz and 5.8GHz would be improved by using POA. The reduced current collapse was observed by using POA. No matter at the high frequency noise or low frequency noise, the observation of device characteristics would improve the noise level. The post-oxide annealing can effectively improve the characteristics of GaN HEMTs and make its applications more comprehensive.