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 (N_D−N_A) and (w_s+w_i), the sum of the surface and interface free‐carrier depletion widths, respectively. The C‐V measurements verify the value of N_D−N_A, and also give a good estimate of w_i. By comparing the value of w_i 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.