Effects of Internal Gain and Illumination-Induced Stored Charges in MgZnO Metal–Semiconductor–Metal Photodetectors

Abstract

The effects of the internal gain originated from the trapping of minority carriers and illumination-induced stored charges have been investigated systematically in MgZnO metal–semiconductor–metal (MSM) photodetectors (PDs) by a proposed semianalytical equivalent circuit model with the basic semiconductor equations and the external parasitic elements taken into account. To verify the accuracy and effectiveness of this model, the simulated steady and transient results are compared with the reported experimental data. It is found that a fall time of 400 ns, much longer than the response time with no internal gain, is attributed to the hole trapping process, inducing an internal gain with a value of 181. In addition, for the high input optical pulse energy (above 10 pJ), the time-delay of the response is caused by the stored charges. This paper indicates that it is very important to improve the MgZnO thin-film quality and balance the optical gain with the response speed. Meanwhile, a reasonable compromise should be found between the energy level of the optical pulse and the bias voltage to minimize the stored charges effect for practical applications. This paper is helpful for the design of high-speed and high-power MgZnO MSM PDs.