An Investigation on the Impact of Aluminum Contact’s Properties on the Performance of Si-MSM Photodetector

Metal-Semiconductor-Metal photodetectors consist of two metallic contacts and an aperture for photon absorption. An MSM photodetector has low dark current, because one of the contacts is always in the reverse bias region. In this paper, we studied the impact of aluminum (metal contact) characteristics on the dark current, photocurrent, and photo-response of a silicon-based MSM photodetector. Metal work function has a small variation in different deposition processes. Impact of metal work function and layer thickness on the performance of MSM photodetector are studied. To this aim, an MSM photodetector is simulated and the dark current, photocurrent, and the photo-response of the structure are investigated. The analyses show that aluminum work function and thickness have a direct effect on the dark current, photocurrent, and photo-response of the photodetector which can change the structure from a photovoltaic to a photoconductive device if the mentioned parameters are not selected well. Therefore, these parameters should be optimized in the design stage. In this study, for a symmetric MSM photodetector, the optimal work function was achieved to be 4.26 eV. Work functions less than this value result in an ohmic contact between the aluminum layer and the silicon layer, and work functions more than this value result in a Schottky junction with a very low breakdown voltage in the reverse bias region which both regions degrade performance of the photodetector. Moreover, the best aluminum layer thickness was obtained to be 1.1 μm. This thickness leads to the maximized photo-response in the photodetector.