Charge Storage Effects in Pseudomorphic High Electron Mobility Transistors

Abstract

Aleasurements were made of the variation of ultrasonic attenuation in indium between 4.2 'ic and 1.3 " K for longitudinal waves at 50 Mc/s and 90 Mcis and for transverse waves at 50 h4c/s. T h e results were analysed to determine the electronic contribution to the total attenuation. Low-amplitude dislocation attenua. tion was significant. Amplitude-dependent attenuation was investigated qualitatively,The electronic attenuation and the electronic mean free path were very anisotropic, The transverse normal-state attenuation decreased with decreasing temperature, In spite of the increasing mean free path. T h e results are discussed in terms of a sue gested mean free path reduction near the edges of the Fermi surface in the reduced. zone scheme. T h e anisotropies are attributed to the combination of a sharply peaked electronic distribution function under the action of the ultrasonic wave, a Fermi surface with sharp edges, and a high probability of small-momentum scattering by thermal phonons For propagation along [110] the value of the average deformation parameter Ki is calculated to be equal to the free-electron value. For propagation normal to (111) K, is 267A greater than this value. These results, together with the large observed transverse attenuation in the superconducting state, indicate that band structure effects on the deformation parameters for indium are appreciable.