Thermal annealing Effects of Ni-Ta Schottky diodes on n-GaN

• Main Authors: Gin-Liang, 陳俊亮
• Other Authors: Wei-Kuo Chen
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/80064147901582813265

碩士 === 國立交通大學 === 電子物理系 === 88 === We have carried out a systematic study of Ni/Ta/n-GaN bilayer Schottky contacts on various thermal annealing conditions by using current-voltage (I-V), Auger electron spectroscopy (AES), and X-ray photoemission spectroscopy (XPS) measurements. In order to get a better understanding of its carrier transport, pure Ta and pure Ni element Schottky diodes were also investigated for comparison. Our experimental results indicate that despite of different barrier height values, the as-deposited samples exhibit well-behaved Schottky properties, regardless of which type of GaN diodes. Nevertheless, upon thermal annealing the Ni diodes were found to be unstable at temperature ³600 oC. Its barrier height is decreased from 0.85 to 0.70 eV as the temperature is increased from 600 to 800oC. On the other hand, very different manners were observed for both Ta and Ni/Ta Schottky diodes under the thermal treatment. The Ta diode shows nonrectifying features at low annealing temperatures, and eventually become insulator-like I-V characteristics for temperatures above 700oC. For Ni/Ta diodes, basically its diode performance at low annealing temperatures is very similar to that of Ta diode, suggesting their carrier transports are governed predominantly by the interfacial status of Ta/GaN metal-semiconductor hetero interface. Nevertheless, when the annealing temperature is further increased to >600 oC, thermally stable excellent Schottky diodes were obtained. The corresponding barrier height and ideality factor lie in the range of 0.9-1.25 eV and 1.08-1.2, respectively. Such a high barrier height in Ni/Ta can be attributed to the formation of tantalum oxide intermediate layer between Ni metal film and GaN substrate, which prevents a sever interdiffusion of Ta and Ni and an evolution of their phase separation to deteriorate the device performance. Since the tantalum oxide is so stable, together with its unique properties that our high-temperature Ni/Ta/GaN diode not only possesses a highest GaN barrier height value, but also can endure hostile thermal treatment environment up to 700oC for one hour. All of the evidences show the Ni/Ta bilayer is nearly an ideal Schottky contact for GaN and has great potential for use in high temperature and high power electronic devices.