2-DIMENSIONAL DEVICE MODELING AND ANALYSIS OF GAINAS METAL-SEMICONDUCTOR-METAL PHOTODIODE STRUCTURES

A two-dimensional self-consistent time-dependent simulation technique has been developed to investigate electron-hole transport processes in the active region of metal-semiconductor-metal (MSM) interdigitated p hotodiode structures and to analyze their high-speed response. The dis tribution of the electric field inside the MSM device is determined by numerically solving the two-dimensional Poisson's equation by the mod ified fast elliptic solver method. A set of superparticles photogenera ted at a particular wavelength is analyzed with a given initial distri bution of the potential and given boundary conditions, and the evoluti on of the particles is traced in time through the active region of the MSM device. Circuit loading, electric field effects in the MSM struct ure with various finger separations, background doping, carrier trappi ng, and recombination are included in the simulation program. Owing to miniaturization of devices, the classical scaling laws lose their val idity while various performance degrading effects appear. The simulati ons show that the main problem in MSM devices with a small contact sep aration is the low electric field penetration depth. This results in d ifferent electron and hole collection rates and in a poor response tim e. The trade-off between the high-speed response and the internal quan tum efficiency is examined and ways to improve the high-speed response are indicated. Modeling results are compared with experimental data o n Ga0.47In0.53As based MSM photodiodes. (C) 1996 American Institute of Physics.