Electrical characterization of molecular beam epitaxial GaAs with peak electron mobilities up to ≊4×105 cm2 V−1 s−1

The effect of varying the temperature (T cr) of an As4→As2 cracker furnace between 600 and 700 °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‐1013 cm−3 concentrations under As2‐growth conditions (T cr=700 °C). By lowering T cr, the silicon concentration is reduced substantially, leaving sulphur as the principal impurity. A 15‐μm‐thick layer grown with T cr=650 °C has measured free‐electron densities of ≊2.8×1013 cm−3 and peak mobilities ≊4×105 cm2 V−1 s−1 at ≊28–42 K, the highest ever recorded in bulk GaAs.