A temperature-independent capacitance in semiconductor-insulator- semiconductor capacitors

Both measurements of capacitance-voltage (C-V) curves of n- GaAs-undoped AlxGa1- xAs- n+ GaAs (AlGaAs) capacitors at different temperatures, and calculations of C-V curves of semiconductor-insulator-semiconductor (SIS) capacitors at different temperatures, show that there is a temperature-invariant capacitance C C and voltage VC at which C-V curves at different temperatures intersect. We show that this is a general property of SIS capacitors having a degenerate gate and nondegenerate substrate of the same doping type, and that qVC, where q is the electron charge, is approximately equal to the Fermi energy of the degenerate GaAs gate. V C provides a good estimate for the voltage required to establish an accumulation layer on n- GaAs at low temperatures, which is determined from magnetotunneling measurements on AlGaAs capacitors.