Momentum relaxation of 2D electron gas due to near-surface acoustic phonon scattering

This study addresses the effect of proximity of a quantum well to a stress-free surface of the semiconductor heterostructure on the momentum relaxation rate of two-dimensional electrons interacting with acoustic phonons via piezoelectric and deformation potentials. The results obtained demonstrate that for narrow quantum wells placed close to the surface the relaxation rate at low temperatures (Bloch-Gruneisen regime) is changed considerably in comparison with that of a two-dimensional electron gas placed in a bulk of semiconductor. For the temperatures where the piezoelectric potential interaction dominates over the deformation potential interaction, the near-surface relaxation rate is enhanced in the case of a semiconductor-vacuum system and is suppressed in the case of the surface covered by a thin metal film. The temperature dependence of the near-surface momentum relaxation rate is found to be T-alpha for values of T far below the Bloch-Gruneisen temperature. For a semiconductor-vacuum system, alpha = 3 and 5 for piezoelectric and deformation potential scattering, respectively; for a semiconductor-metal system, alpha = 5 for both mechanisms. It is predicted that screening changes the temperature dependences of momentum relaxation rates: for a semiconductor-vacuum system, alpha = 5 and 7 for piezoelectric and deformation potential scattering, respectively. Screening does not change a in the case of metal-semiconductor system. (C) 1999 Elsevier Science B.V. All rights reserved.