Electronic Transport Properties of Semiconductor Microstructures

In this dissertation we investigate the momentum and energy relaxation properties of a 2D EG at the interface of a high-mobility, modulation doped Al_ {rm x}Ga_{rm 1-x}As/GaAs heterojunction. Our work consists of four main parts. In the first part we study the bulk phonon scattering contribution to the transport properties of a two-dimensional electron gas formed at the interface of an ultra-pure Al _{rm x}Ga _{rm 1-x}As/GaAs heterojunction. Our work encompasses three physically distinct temperature ranges with respect to phonon scattering; the Bloch-Gruneisen (BG), equipartition (EP), and inelastic scattering regimes. To evaluate the mobility in the inelastic scattering regime at high temperatures above T~ 40 K, where the scattering from polar LO-phonons becomes important, we compute that first order perturbation distribution phi(E) as function of the carrier energy E by directly solving the linearized Boltzmann equation by an interative method. In part two we investigate in detail the temperature dependence of the mobility at low temperatures in the range T = 4-40 K, and density range (0.3-6.0) times 10^{11 } cm^{-2} due to acoustic-phonon scattering. In agreement with experimental results, we show that the linear coefficient of the temperature dependence alpha = dmu ^{-1}(T)/dT has a shallow minimum as a function of the electron density. The energy relaxation properties of a 2D EG in Al_{rm x}Ga _{rm 1-x}As/GaAs heterojunctions are investigated in part three. The total average energy -loss rate at low temperatures is calculated for various densities and temperatures. We take into account the inelastic -scattering mechanisms due to acoustic phonons by deformation -potential and piezoelectric coupling, and the low-energy phonons associated with the coupling of quasiparticle excitations to the LO phonons. Finally, in the fourth part we study the effects of impurity scattering from the remote donors on a 2D EG using the Born approximation. We carry out a simple model calculation to investigate the spatial correlation effect of the ionized scattering sites on the electron mobility.