FENG Zhi-Hong1**, WANG Xian-Bin1,2, WANG Li3, LV Yuan-Jie1, FANG Yu-Long1, DUN Shao-Bo1, ZHAO Zheng-Ping1,2
1National Key Laboratory of Application Specific Integrated Circuit (ASIC), Hebei Semiconductor Research Institute, Shijiazhuang 050051 2School of Information Engineering, Hebei University of Technology, Tianjin 300019 3Information Center of Science and Technology, Beijing 100085
Abstract：Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N-polar GaN, the Al metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOx. In addition, the formation of AlOx is affected by the Al layer thickness greatly. The AlOx combined with the presence of AlN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the Al layer thickness to some extent, less AlOx and AlN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity ρ of 1.97×10?6 Ω?cm2 is achieved with the Al layer thickness of 80 nm.
2015, Vol. 32 
