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

This study addresses the effect of proximity of a quantum well to a stress- free surface of the semiconductor heterostructure on the momentum relaxatio n rate of two-dimensional electrons interacting with acoustic phonons via p iezoelectric and deformation potentials. The results obtained demonstrate t hat for narrow quantum wells placed close to the surface the relaxation rat e at low temperatures (Bloch-Gruneisen regime) is changed considerably in c omparison with that of a two-dimensional electron gas placed in a bulk of s emiconductor. For the temperatures where the piezoelectric potential intera ction dominates over the deformation potential interaction, the near-surfac e 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 temperatu re. For a semiconductor-vacuum system, alpha = 3 and 5 for piezoelectric an d deformation potential scattering, respectively; for a semiconductor-metal system, alpha = 5 for both mechanisms. It is predicted that screening chan ges the temperature dependences of momentum relaxation rates: for a semicon ductor-vacuum system, alpha = 5 and 7 for piezoelectric and deformation pot ential scattering, respectively. Screening does not change a in the case of metal-semiconductor system. (C) 1999 Elsevier Science B.V. All rights rese rved.