Abstract

A figure of merit often used to characterize ultrafast photoswitches and detectors based on semiconductors such as GaAs is the ratio of responsivity (amps or volts per watt) and carrier recombination time. During the past decade attempts to optimize this parameter usually have involved reduction of the carrier life time by ion-implantation. At the highest implantation levels, however, where picosecond response can be achieved, the responsivity can become severely reduced. Recently it has been found that GaAs grown at low-temperature grown GaAs by molecular beam epitaxy has reasonably high carrier mobility while possessing a carrier lifetime of less than a picosec- ond.^[1,2] At a fundamental level little is known about the carrier distributions in this material. We have used time-resolved photoluminescence techniques to characterize the carrier distributions in this material and compared them with similar measurements made for a series of proton-implanted GaAs (GaAs:H) specimens having response times as short as 500 fs.^[3] Besides the relevance to device performance, these ultra-short lifetime materials also provide a unique opportunity to study nonequilibrium carrier effects in materials where the recombination time is comparable to other time constants which determine the evolution of the carrier distributions. In addition the short recombination time effectively serves as a “time gate” making it possible to observe nonequilibrium carrier distributions even under quasi-cw excitation.

© 1992 IQEC