ELECTROREFLECTANCE INVESTIGATION OF TRAPPING STATES AT SIO2 GAAS INTERFACES/

Electroreflectance spectroscopy is applied to evaluate energy distribu tions of interface-state densities in GaAs-based metal-insulator-semic onductor diodes. In this method, bias-voltage dependence of surface Fe rmi-level positions is obtained by directly measuring the magnitude of semiconductor surface electric fields via analysis of the Franz-Keldy sh 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 valen ce band is pinned at E-C - 0.88 eV, where a steep rise in the interfac e-state density was observed. The method is free from the uncertaintie s 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.