DISLOCATION SCATTERING IN N-TYPE MODULATION DOPED AL0.3GA0.7AS/INXGA1-XAS/AL0.3GA0.7AS QUANTUM-WELLS

The mobility limited by dislocation scattering has been calculated for n-type modulation doped Al0.3Ga0.7As/InxGa1-xAs/Al0.3Ga0.7As quantum wells. Dislocations are approximated by three groups of infinitely long dislocation lines oriented in an orthogonal array, and both the coulombic and piezoelectric potentials are considered. It is found that for the z-direction dislocations, the coulombic potential yields an overall mobility of 3.6 x 10(3) cm2/V . s with an anisotropy of approximately 5% due to the piezoelectric potential, where the concentration of indium x = 0.5, the well width L = 50 angstrom, the sheet density of electrons n = 4.093 x 10(12) cm-2, and the flux-like dislocation density N(z) = 10(10) cm-2. In contrast, for the x- and y-direction dislocations, with the flux-like dislocation density N(x) = N(y) = 10(10) cm-2, the overall mobility is of 3.6 x 10(4) cm2/V . s with an anisotropy of approximately 50% mainly due to the coulombic potential. If the overall mobility for a fixed field direction is evaluated as a function of indium percentage x at fixed well width L, the mobility is found to decrease rapidly with increasing x for small x and more slowly for larger x. For dislocation densities on the order of 10(10) cm-2, the z-direction dislocation scattering is the dominant mobility-degraded mechanism over other elastic scattering mechanisms such as interface roughness scattering, impurity scattering, and alloy disorder scattering, and may severely limit the mobility of n-type modulation doped quantum well devices.