Study On The Ohmic Contact Of N-type GaN

Recently, GaN material becomes the research focus of solid state lighting, digital process, optoelectronic devices and power devices because of its perfect light and electric characterizations. Most commercial GaN based light-emitting diodes (LEDs) are grown on the sapphire substrate or silicon carbide (SiC) substrate by metal-organic chemical vapor deposition (MOCVD). Compared with SiC substrate, sapphire substrate has many advantages, such as lower price, mature production process technology. The problems of current crowding, high voltage and bad heat radiation have been successfully solved, which provides technology foundation of high-power LED manufacture.As the development of the semiconductor technology, the ohmic contact property of GaN based LEDs needs further improvement. The ohmic contact directly influences the reality, life time and efficiency of the device. The study of the ohmic contact on N型GaN is very important to decrease the voltage, improve the operation stability of the device and increase the life time of the device.In this paper, we fabricate ohmic contact pad on n-type GaN and calculate the specific contact resistivity of the ohmic contact by transmission line model (TLM). We investigate the measurement method and fabrication process of the ohmic contact pads on n-type GaN. The research results are as following:(1). The Ti/Al/Ti/Au metal mutil-layers were chosen as the ohmic contact pads on n-type GaN with the doping concentration of3×1018cm-3.(2). We studied the line-TLM and circle-TLM and found circle-TLM was better to characterize the ohmic contact on n-type GaN. The specific contact resistivity is about3.23×10-6Ω·cm2.(3). We investigated the influence of the annealing temperature on the property of the ohmic contact. The specific contact resistivity decreases as the temperature to800℃from600℃. When the annealing temperature further increases to900℃, the specific contact resistivity increases a little. The smallest specific contact resistivity with800℃annealing temperature...