C.T. Lee, S.M. Jung, M.W. Shin
Yonsei University, Korea
pp. 159 - 161
Keywords: pH sensor, AlGaN/GaN heterostructure
In this work, we evaluated relationship between specific contact resistance and sensitivity of pH sensor by changing the ohmic contact metallization consisted of source and drain. The sample was fabricated for analysis of electrical characteristics and sensitivity. The AlGaN/GaN structure was a commercial wafer provided by NTT-AT and grown on a 6-inch Si(111) wafer by MOCVD. The structure consisted of a ~4-um C-doped GaN buffer layer and a ~300-nm i-GaN layer and ~20-nm Al0.25Ga0.75N barrier with a ~2-nm i-GaN cap layer. The drain and source electrodes were formed by deposition of ohmic multilayers, annealing process at 850OC for 30s by RTA system and conventional lift-off process as shown in Figure 1. The device was covered with 300-nm-thick SiO2 film using PECVD to prevent chemical reaction and the open-gate area was fabricated through photolithography and wet etching processes . We measured specific contact resistance value of ohmic contact using TLM patterns. The I-V characteristic was measured by four-probe method. The sensitivity of pH was measured by pH meter. All data were measured from room temperature to 80 OC.