Dielectric Spectroscopy Of Semiconductors

Dielectric spectroscopy of semiconductors (DSS) employs dielectric measuring techniques to study delayed electronic transitions in and out of localised energy levels in the forbidden gap. Horizontal transitions between levels normally take place in the volume of the material and involve relatively small changes of energy. Vertical transitions between deep levels and the free bands involve energy changes of the order of half the band gap and take place mainly in interfacial space charge regions ad at semi-conductor-metal interfaces. DSS is uniquely able to resolve the spectra of these delayed transitions and measurements on semi-insulating GaAs in the frequency range .01 - 10,000 Hz and between 90 and 380 K show that none of them conforms to the expected exponential time dependence. Measurements are reported of the dielectric response in the frequency range .01 - 10,000 Hz of Schottky diodes on n-type GaAs with aluminum metallisation, with the results revealing several important deviations from the classically expected response. The most important and unexpected phenomena are the appearance of low-frequency dispersion (LFD) and of negative capacitance, which are strongly influenced by even small (0.1V) negative capacitance, which are strongly influenced by even small (0.1V) negative and positive biases, respectively. Both phenomena are linked with interfacial processes involving some form of instability arising from structural transformations at the metal semiconductor interface.