OBSERVATION OF SWITCHING ENERGY-DEPENDENCE ON ILLUMINATING BEAM AREA IN THE VSTEP OPTOELECTRONIC SWITCH

We have observed a strong dependence of the optical switching energy o f a p-n-p-n VSTEP device on the area of the illuminated spot. We expla in the area dependence in terms of a long diffusion time (approximatel y 1 mus) required for the photo-generated holes to reach a uniform dis tribution in the depleted p-layer and report results of a carrier diff usion calculation which supports this conclusion. This effect reduces the required optical switching energy by as much as a factor of five f or the devices measured.