SURFACE AND INTERFACE FREE-CARRIER DEPLETION IN GAAS MOLECULAR-BEAM EPITAXIAL LAYERS - DEMONSTRATION OF HIGH INTERFACE CHARGE

Molecular beam epitaxial GaAs layers of electron concentration 1.69×1017 cm-3, and various thicknesses d=0.25, 0.50, 1.00, and 2.00 μm, have been grown on semi-insulating GaAs substrates and characterized by the Hall effect and capacitance-voltage (C-V) techniques. A plot of sheet Hall concentration n s vs d gives accurate values of (ND-NA) and (ws+wi), the sum of the surface and interface free-carrier depletion widths, respectively. The C-V measurements verify the value of N D-NA, and also give a good estimate of wi. By comparing the value of wi with depletion theory, it is shown unambiguously that the interface depletion is mainly due to interface states, of concentration 1.2×1012 cm-2 (below midgap). This result has important technological implications.