TRANSPORT MODELING OF MULTIPLE-QUANTUM-WELL OPTICALLY ADDRESSED SPATIAL LIGHT MODULATORS

A transient, two-dimensional drift-diffusion model is developed for op tically addressed spatial light modulators made with quantum-well mate rials. The transport of free and well-confined carriers is considered along with nonlinear transport effects such as velocity saturation, fi eld-dependent carrier escape from quantum wells, and resonant absorpti on. In addition to full numerical solutions to the transport equations , analytical and simplified numerical solutions are developed to descr ibe basic screening behavior and to give estimates of speed and resolu tion performance. In particular, a self-consistent small signal model is developed to justify the surface-charge picture often used to descr ibe device operation. This model is also used to simulate grating form ation and decay. It is found that the maximum screening rate and peak grating amplitude are achieved using vertical drift lengths much longe r than the device length. A detailed analysis of resolution performanc e is also given in which the effects of transit time, carrier lifetime , and free and confined transport along the wells are simulated. For t ypical device parameters, the two main limitations to resolution perfo rmance are found to be anisotropic drift in the interior due to the qu antum wells and transverse drift along the device interfaces. Two devi ce designs an compared to assess the ability to optimize device perfor mance by changing experimentally accessible parameters such as carrier lifetime and quantum-well escape rates. Resolutions down to 7 mu m an d frame rates of 100 kHz at 10 mW/cm(2) are achieved. (C) 1997 America n Institute of Physics.