Low-Field Phonon-Limited Mobility in Semiconducting Heterojunction Structures

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Abstract
We have calculated the drift mobility of a quasi-two-dimensional electron gas at an AlGaAs/GaAs interface as limited by acoustic deformation and polar optical phonon scattering, using a relaxation time approximation for the electron distribution function and a momentum-conservation description of the confined motion. The confining potential profile was modeled by an infinite triangular well and by a finite asymmetric square well. Mobility calculations included inter- as well as intra-subband scattering. We have found that the scattering rate is considerably larger than the momentum relaxation rate. Both rates show discontinuities at a multiplicity of energies due to the existence of bound states in the wells. As expected, the mobilities calculated from the momentum relaxation time are larger than those given by the scattering rate and therefore compare more closely with the experimental data. At a given temperature, the calculated mobility as a function of internal field F (square well width d) is dominated by polar optical scattering at lower F (larger d) but by acoustic scattering at higher F (smaller d).