Far-infrared photo–Hall experiments on GaAs:Si

Using far-infrared radiation from the free-electron laser at the University of California, Santa Barbara, high-power photoconductivity experiments were performed on n-type GaAs:Si. In order to distinguish among the various mechanisms of the observed photoconductivity, we simultaneously monitored the Hall voltage and the photocurrent created by the photoexcited electrons. In this way the number and mobility of the electrons contributing to the photoconductivity were determined. At 4.2 K and in weak magnetic fields, 200- and 295-μm radiation in high-power pulses of 2-μsec duration was used to excite donor electrons from the bound 1s ground state. The experiments show that the photoconductivity arises from electrons that are excited into the conduction band, where they are further heated by the radiation.