Characterization of high purity GaAs far-infrared photoconductors

In this paper we report the results of an extensive study on the far-infrared photoconductivity of high purityn-type GaAs. The crystal, which was grown at Max-Plank-Institute for Solid State Physics using liquid-phase epitaxy, exhibited the fine structures of the excited state transitions of the residual shallow level impurities. The major peak in the spectral response belongs to the 1s-2p transition, with its responsivity about thirty five times higher than the continuum. At 3.4K detector temperature, 625 mV bias, and 100 Hz chopping frequency the detector responsivity at 35.4 cm−1 (279 µm) was measured to be 0.017 A/W. Under these same conditions, the NEP was 5.9×10−14 W/√Hz. The (DC) dark current at 25 mV bias was 5.6×10−14 A.