Carrier Mobilities in Delta-doped Heterostructures

For applications to sensor design, the product nxmu of the electron density n and the mobility mu is a key parameter to be optimized for enhanced device sensitivity. We model the carrier mobility in a two dimensional electron gas (2DEG) layer developed in a delta-doped heterostructure. The subband energy levels, electron wave functions, and the band-edge profile are obtained by numerically solving the Schrodinger and Poisson equations self-consistently. The electron mobility is calculated by including contributions of scattering from ionized impurities, the background neutral impurities, the deformation potential acoustic phonons, and the polar optical phonons. We calculate the dependencies of nxmu on temperature, spacer layer thickness, doping density, and the quantum well thickness. The model is applied to delta-doped quantum well heterostructures of AlInSb-InSb. At low temperature, mobilities as high as 1.3x10^3 m^2/Vs are calculated for large spacer layers (400 A) and well widths (400 A). The corresponding room temperature mobility is 10 m^2/Vs. The dependence of nxmu shows a maximum for a spacer thickness of 300 A for higher background impurity densities while it continues to increase monotonically for lower background impurity densities; this has implications for sensor design.