THE GROWTH OF SHALLOW HIGH MOBILITY 2-DIMENSIONAL ELECTRON-GAS STRUCTURES

GaAs/AlAs heterostructures are described in which the two-dimensional electron gases (2DEGs) are in close proximity to the crystalline surface. Measurements are presented from samples in which the 2DEGs were 15 and 25 nm below the GaAs/vacuum interface. The sheet carrier concentrations were 6.7 x 10(11) and 3.4 x 10(11) cm-2 and Hall mobilities were 5 x 10(5) and 1.2 x 10(6) cm2 V-1 s-1, respectively, at 4 K. The two samples were examined by transmission electron microscopy. Hall measurements are given both as a function of temperature and as a function of surface Schottky gate voltage at 4 K. A simple capacitor model was used to relate the sheet carrier concentration versus gate voltage dependence to the depth of the 2DEG below the gate. Variable temperature Hall measurements suggest that ionized impurity scattering is less significant than phonon scattering at 4 K.