Enhanced high-speed photoresponse by diffusion of iron into undoped semi-insulating GaAs

Responses to picosecond light pulses have been compared on undoped liquid encapsulated Czochralski (LEC) semi-insulating wafers with and without iron doping. A large photocurrent, especially at the leading edge, for the iron-doped sample is expected because of increased hole capturing by the deep acceptors of iron, as well as decreased electron capturing caused by a concomitant decrease of deep donors such as EL2 and EL6. This was confirmed by the photocurrent decay at higher excitation, which is dominated by electrons in iron doped case, in contrast to holes in the undoped case.