Electroreflectance investigation of trapping states at SiO,/GaAs interfaces

Electroreflectance spectroscopy is applied to evaluate energy distributions of interface-state densities in GaAs-based metal-insulator-semiconductor diodes. In this method, bias-voltage dependence of surface Fermi-level positions is obtained by directly measuring the magnitude of semiconductor surface electric fields via analysis of the Franz-Keldysh oscillation spectra. An enhanced accuracy is available through the use of undoped/n+-GaAs junction structures for the test diodes. The result indicates that movement of surface Fermi-level toward the valence band is pinned at EC - 0.88 eV, where a steep rise in the interface-state density was observed. The method is free from the uncertainties experienced in the conventional capacitance technique, when applied to trap-rich interfaces, and thus, is useful in elucidating interface-originated problems in GaAs-based devices.