THEORETICAL-STUDY OF THE EFFECT OF AN ALGAAS DOUBLE-HETEROSTRUCTURE ON METAL-SEMICONDUCTOR-METAL PHOTODETECTOR PERFORMANCE

The impulse and square-wave input response of different GaAs metal-sem iconductor-metal photodetector (MSM) designs are theoretically examine d using a two dimensional drift-diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunc tions. The rise time and the fall time of the output signal current ar e calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double hete rostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active, absorption layer and the bottom GaAs substrate. The e ffect of the depth of the AlGaAs layer on the speed and responsivity o f the MSM devices is examined. It is found that there is an optimal de pth, at fixed applied bias, of the AlGaAs layer within the structure t hat provides maximum responsivity at minimal compromise in speed.