Reducing dark current in a high-speed Si-based interdigitated trench-electrode MSM photodetector

The authors have studied higher dark-current temperature dependence in a trench-electrode Si-based metal-semiconductor-metal (MSM) photodetector which has a hydrogenated intrinsic amorphous silicon (i-a-Si:H) dark-current suppression layer. The poor dark-current temperature-dependence performance could be improved significantly by reducing the number of trap states in the depletion region of the reverse-biased crystalline/amorphous Si heterojunction. To reduce the trap states, a modified plasma-enhanced chemical vapor deposition (PECVD) system, which reduced the ion bombardment on the Si substrate, was employed to deposit an i-a-Si:H layer. Moreover, since fewer trap states in a photodetector will result in a degradation of the fall time of the temporal response of the device, a Ti electrode, which has a lower Schottky barrier height (0.62 eV) than that (0.84 eV) of the previous Cr electrode used with i-a-Si:H, was employed for compensation. The device obtained exhibited very good dark-current stability and temporal response. The dark current only increased from 6 to 34 nA, when the operating temperature was increased from room temperature (R. T.) to 57°C, much lower than that of the previously reported 3-V bias voltage one (from 22 to 209 nA). Device responsivity and quantum efficiency also showed obvious improvement, both at R. T. (0.192 A/W and 0.29) and 57°C (0.213 A/W and 0.32, respectively) and were higher than those previously reported (0.174 A/W and 0.26, at 57°C).