PHOTOEXCITED HOT-ELECTRON RELAXATION PROCESSES IN N-HGCDTE THROUGH IMPACT IONIZATION INTO TRAPS

In this article we report on a new type of spectroscopy for impurity and/or defect levels in the energy gap of narrow-gap semiconductors using the near-band-gap photon energies from a laser. This spectroscopy is done under the conditions of intense laser photoexcitation and is associated with the Auger relaxation processes of hot electrons involving impact ionization of valence electrons into impurity of defect levels. Wavelength-independent structure in the photoconductive response versus magnetic field is observed at high intensities in samples of Hg1-xCd(x)Te with x almost-equal-to 0.22 and 0.24. This structure arises from hot electrons photoexcited high into the conduction band by sequential absorption of CO2 laser radiation. The hot electrons lose their energy by impact ionizing valence electrons into impurity/defect levels in the gap. For the sample with x almost-equal-to 0.22 and an energy gap of 95 meV, three levels are found at 15, 45, and 59 meV above the valence band. A level at 61 meV is found for the sample with x almost-equal-to 0.24 and a gap of 122 meV.