Theoretical study of the response of InGaAs metal-semiconductor-metal photodetectors

We present a theoretical investigation of the response of metal-semiconductor-metal (MSM) photodetectors made of InGaAs lattice-matched to InP using a two-dimensional drift-diffusion model with a thermionic-field emission boundary condition for the heterojunctions. The effect of including a top InAlAs layer to increase the effective barrier height of the metal fingers on the InGaAs active layer is thoroughly examined and found to limit the collection of the photocurrent signal due to the electron and hole barriers that it forms with InGaAs. Due to the thickness and height of the InAlAs barrier layer in existing designs, the tunneling current obtained from the model is found to be negligibly small to significantly affect the output signal current. In an attempt to obtain a better response, different design structures including one where a quasi-Schottky contact is utilized are studied and their speed of response, breakdown voltage, and dark current are compared to that of the usual InGaAs device.