Sub-terahertz response of stressed and unstressed Ge:Ga photoconductive detectors

Ge:Ga is a widely used detector material for applications at terahertz frequencies. Its response ranges from about 40 /spl mu/m -120 /spl mu/m. If a compressive force is applied to the crystal the response shifts to about 100 /spl mu/m - 240 /spl mu/m. We report on a long wavelength, sub-terahertz response >300 /spl mu/m. This response can be attributed to transitions from excited Ga states into the valence band. The results indicate that a cascade type of relaxation exists in Ge:Ga at 4.5 K.