Cryogenic processed metalsemiconductormetal (msm) photodetectors on mbe grown znse

Molecular beam epitaxy grown 0.5μm and 2.0jurn thick undoped ZnSe on semiinsulating (100) GaAs substrates were prepared for metalsemiconductormetal (MSM) photodetector devices. The MSM photodetectors consisted of interdigitated metal fingers with 2, 3, and 4 μm width/spacing on a wafer. A multilayer resist process was employed using polyimide and SiO₂ thin films before the pattern generation to aid in a special low temperature (LT) liftoff process. Dark currentvoltage (IV), DC photo IV, highfrequency IV, spectral response, and frequency response techniques were employed for testing the device performance. The cryogenic processed metallization provided an improved interface between metal and semiconductor interface. The breakdown voltage in these devices is dependent on the electrode width/spacing and not on film thickness. Dark current remained at around 1 pA for a bias of ±10 V. The devices exhibited a high spectral responsivity of 0.6 (A/W) at a wavelength of 460 nm at 5 V applied bias. A maximum spectral responsivity of 1 (A/W) at an applied bias of 5 V was obtained in these devices indicating an internal gain mechanism. This internal gain mechanism is attributed to hole accumulation in ZnSe epilayers.