Nonlinear absorption in semiconductor single heterostructure Schottky barrier structures
Lengthening carrier lifetimes is possible in semiconductors by separating holes and electrons. However, large nonlinear optical effects require large charge densities, which can be achieved through confinement of carriers. These ideas have been combined in a heterostructure depletion geometry that confines electrons and removes holes. The results show carrier lifetimes of 4 μs and improvements in the sensitivity of the bandfilling nonlinearity by 500 times over bulk, resulting in a measured 30% change in absorption at 4 W/cm2. A unique feature of these devices is a carrier-dependent lifetime that is a strong function of incident light. This makes possible nonequilibrium situations in which nonlinearities are much larger than predicted on a CW basis. The energy band diagram and the optical response to longer pulses are shown and discussed. The transmission of a high-input-intensity (4 W/cm2) pulse is plotted as a function of the time-integrated energy density incident on the samples for a lifetime of 4.3 μs.