Abstract

One form of the VSTEP device is a bistable light activated thyristor with an optically active region, between two AlGaAs/ GaAs heterojunctions, for light emission. We report a nearly linear dependence of the optical switching energy E_sw on illumination area showing a factor of 5 decrease in the minimum E_sw as the spot size is reduced 10 times from the full device area. This effect is explained by noting that the inner p layer is completely depleted and the mobility of the photogenerated holes, injected into this region as part of the current flow mechanism, is very low. For small illumination areas and sufficiently high powers, the device can be made to switch on (initially, only in this small area) in a time that is short compared with the lateral spreading time (~400 ns). The total optical energy required to accomplish this is linearly dependent on the illumination area in this limit. For lower power densities, when switching times are longer than this characteristic time, E_sw becomes independent of the spot size. We see evidence of this behavior in the data. Calculations of E_sw for the fully illuminated device show good agreement with the measurements.

© 1992 Optical Society of America