ALLOY SCATTERING AND LATTICE STRAIN EFFECTS ON THE ELECTRON-MOBILITY IN IN1-XGAXAS

Electron mobility and resistivity in In1-xGaxAs alloys are calculated as a function of x for ionized impurity densities from 10(15) to 10(18) cm-3 and temperatures between 77 and 400 K. Mobility as a function of the compositional parameter x is calculated by using the Mattheissen formalism to combine impurity, acoustic phonon, optical phonon and alloy scattering contributions. The calculated mobilities at 300 and 77 K are found to be in good agreement with experimental results. At 300 K, the optical polar mode is the mobility limiting process and alloy scattering contributes about 5% at x = 0.1 to 30% at x = 0.7. At 77 K, ionized-impurity scattering is the limiting process for N(I) greater-than-or-equal-to 5 x 10(16) cm-3, and alloy scattering is also significant over a large portion of x, with a maximum of 37% of the electron mobility at x = 0.7. Alloy scattering is found to be important (over a large portion of composition) at lower temperatures and low impurity densities, supporting the view that alloy scattering will preclude very high mobility in In1-xGaxAs quantum well heterostructures. The electron mobilities for x = 0.47 (the composition where low-dimensional device lattices matched with InP are fabricated) as a function of temperature are also calculated and found to agree with experimental data as well as those calculated by more fundamental methods. The electron mobility as a function of the total impurity concentration is also evaluated for x = 0.47. Using the calculated mobilities, the resistivities of In0.53Ga0.47As as a function of temperature and ionized impurity density are also computed. Finally we examine the divergence of experimental mobility from prediction wrought by a lattice strain induced in heretoepitaxial films of In1-x GaxAs (x > 0.8) on GaAs substrates. Layers deposited by vapour phase epitaxy have carrier concentrations ranging from 10(16) to 10(18) cm-3 and mobilities between 1.7 and 8.5 x 10(3) cm-2 V-1 s-1 at 300 K. These data show that lattice mismatch induced strain in In1-xGaxAs films on GaAs substrates has a significant effect on the mobility, commensurate with that reported for the same compound on InP substrates.