Characteristic of ZnO transparent conducting oxides and their application to GaN Schottky barrier diodes

• Main Authors: Kuo-Hua Chang, 張國華
• Other Authors: Jinn-Kong Sheu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/35103443593752276600

碩士 === 國立成功大學 === 光電科學與工程研究所 === 94 === In this study, undoped ZnO and boron-doped ZnO(BZO) films were deposited on sapphire by means of an magnetron sputtering method. The BZO films were prepared by cosputtering of ZnO and B2O3 targets. The as-deposited ZnO films exhibited a high-resistivity property. The BZO thin films were then thermally annealed in nitrogen ambient to achieve the high-transparency andlow-resistivity TCO thin films. After thermal annealing, the resistivities of the GZO films were further reduced at least two orders of magnitude reaching to ~10-3 Ω-cm. This could be attributed to the fact that the reduction of resistivity in annealed BZO films is not solely due to the increase of oxygen vacancy concentration but is also due to the increase of mobility, which is attributable to the increase of grain size after thermal annealing. In contrary to the undoped samples( ZnO films ), a marked blueshift was observed in the transmittance spectra taken from the annealed BZO films indicating the Burstein-Moss effect involved in the transition. In addition, we also demonstrated Ga-doped ZnO(GZO) as Schottky contacts on GaN films. Application of UV photodetector(PD) indicated that spectral responsivity shows a narrow bandpass characteristic ranging from 340 to 370 nm as the GaN films were caped with low-temperature-grown GaN layer having high resistivity. Decreased responsivity in the short-wavelength region (λ<340 nm) can be explained by the marked absorption of the GZO contact layer. Additionally, our findings indicate that when the reverse biases were below 5 V, the dark currents were well below 1×10-11A as the GaN films were caped with low-temperature-grown(LTG) GaN layer having high resistivity. This dark current is far less than that of samples without LTG cap layer.