Electron mobility in low-temperatureHg1−xCdxTeunder high-intensity CO2laser excitation

Abstract

A photo-Hall technique has been employed to determine the dependence of the low-temperature electron mobility in narrow-gap ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Te}$ ($x\ensuremath{\approx}0.2$) on optically generated carrier density. Excitation is provided by C${\mathrm{O}}_{2}$ laser pulses of 200-nsec or 25-\ensuremath{\mu} sec duration. At low excitation levels the mobility is found to increase due to the neutralization of ionized acceptors by the photoexcited holes. At higher excitation levels the mobility decreases due to electron-hole scattering. Comparison is made to a theory which fully incorporates the Kane band model in treating the scattering of electrons by ionized impurities, photoexcited holes, and compositional disorder. The adaptation of the partial-wave phase-shift method to a nonparabolic band structure is discussed. The treatment of electron-hole scattering incorporates a recently developed theory which accounts in detail for the dynamic dielectric response of the lattice polarizability and free carrier screening. With the use of the random-phase-approximation dielectric constant $\ensuremath{\epsilon}(q,\ensuremath{\omega})$ for arbitrary degeneracy, it is found to be particularly important that the screening by photoexcited holes be treated dynamically. Because the mobility increase at low excitation levels is highly sensitive to the number of acceptors present in the sample, the photo-Hall technique is quite promising as a means of accurately determining compensation densities in narrow-gap ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Te}$.