Photoconductive and photovoltaic metal-semiconductor-metal <i>κ</i>-Ga<sub>2</sub>O<sub>3</sub> solar-blind detectors with high rejection ratios
Mei Cui, Yang Xu, Xinyu Sun, Zhengpeng Wang, Hehe Gong, Xuanhu Chen, Tiancheng Hu, Yijun Zhang, Fangfang Ren, Shulin Gu, Jiandong Ye, Rong Zhang
Abstract
Abstract The metal-semiconductor-metal (MSM) structure is a popular architecture for developing Ga 2 O 3 solar blind photodetectors. The nature of metal-semiconductor contact is decisive for the operation mode, gain mechanism and device performances. In this contribution, κ -Ga 2 O 3 MSM solar-blind photodetectors with Ti/Ga 2 O 3 Ohmic and Ni/Ga 2 O 3 Schottky contacts were constructed on the high-quality Si-doped κ -Ga 2 O 3 epilayer grown by hydride vapor phase epitaxy. The Ti/ κ -Ga 2 O 3 /Ti Ohmic MSM device is operated in a photoconductive mode, exhibiting a maximum responsivity of 322.5 A W −1 and a high rejection ratio of over 10 5 , but with an undesirable sub-gap response and high dark current. In comparison, the Ni/Ga 2 O 3 /Ni photodiode with a back-to-back Schottky configuration is operated in a mixed photovoltaic and photoconductive mode, demonstrating a decent photoresponsivity of 0.37 A W −1 , a maintained high rejection ratio of 1.16 × 10 5 , a detectivity of 3.51 × 10 13 Jones and the elimination of slow photoresponse from sub-gap states. The frequency-dependent photoresponse and transient photocurrent characteristics indicate that the persistent photoconductivity effect is responsible for the high gain achieved in the Ti/Ga 2 O 3 /Ti photoconductor, and the dominant slow transient decay component is a fingerprint of photoexcited carrier trapping and repopulation. The response speed is improved in the Ni/Ga 2 O 3 /Ni Schottky MSM device, whereas carrier transport across interdigitated fingers is affected by bulk traps, limiting the overall response-bandwidth merit.