FAR-INFRARED PHOTOCONDUCTIVITY IN HIGH-PURITY EPITAXIAL GaAs

Abstract

Extrinsic far‐infrared photoconductivity has been observed at 4.2°K in high‐purity n‐type epitaxial layers of GaAs grown on Cr‐doped semi‐insulating GaAs substrates. Measurements of the responsivity and noise in the detection system at 300 Hz in a 1‐Hz bandwidth yield an NEP of 1.2 × 10⁻¹¹ W at 195 μ, 1.4 × 10⁻¹² W at 337 μ and 6 × 10⁻¹¹ W at 902 μ. The time constant of the detector has been determined to be shorter than 1 μsec using a Ge avalanche modulator to chop the incident radiation. A time constant of about 5 nsec has been measured using impact impurity ionization in the GaAs.