ELECTRICAL CHARACTERIZATION OF MOLECULAR-BEAM EPITAXIAL GAAS WITH PEAK ELECTRON MOBILITIES UP TO ALMOST-EQUAL-TO-4X10(5)CM(2)V(-1)S(-1)

The effect of varying the temperature (T(cr)) of an As4 --> As2 cracker furnace between 600 and 700-degrees-C on the properties of GaAs grown by molecular beam epitaxy has been evaluated using 4-300 K Hall measurements and 4.2 K far-infrared photoconduction spectroscopy, in an extension of earlier work on high-mobility material (Ref. 1). The residual donors are silicon and sulphur with mid-10(13) cm-3 concentrations under As2-growth conditions (T(cr) = 700-degrees-C). By lowering T(cr), the silicon concentration is reduced substantially, leaving sulphur as the principal impurity. A 15-mu-m-thick layer grown with T(cr) = 650-degrees-C has measured free-electron densities of almost-equal-to 2.8 x 10(13) cm-3 and peak mobilities almost-equal-to 4 x 10(5) cm2V-1s-1 at almost-equal-to 28-42 K, the highest ever recorded in bulk GaAs.