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An approach is presented for comprehensive and reliable analysis of the surface photovoltage (SPV) amplitude and phase spectral behaviour in various semiconductor materials and structures. In this approach the SPV signal is represented as a radial vector with magnitude equal to the SPV amplitude and angle with respect to the x-axis equal to the SPV phase. This model is especially helpful in complicated nanostructures, where more than one SPV formation processes arises during the spectrum run. The value of the proposed model has been demonstrated by the successful explanation of seemingly contradictory SPV amplitude and phase spectra of AlAs/GaAs superlattices with embedded GaAs quantum wells, grown on different GaAs substrates. This has provided useful information about the investigated nanostructures. The need for simultaneous examination of both SPV amplitude and SPV phase spectra in order to obtain a correct understanding of the experimental data is emphasized.

Extrinsic photoconductivity measurements at 70 and 293 K in Cr-doped SI GaAs bulk crystals have been carried out in order to characterise the deep levels in this material. The photoconductivity spectra reveal two characteristic structures extended in the low-energy and the high-energy regions, respectively. It is shown that low-energy structure is connected with the Cr2+ deep acceptor level and the high-energy one with the EL2 deep donor level. The spectrum measured after an intentionally photo-induced transfer of EL2 into its metastable state confirms the authors' interpretation of the origin of the high-energy structure. They believe that their study is the first to identify the EL2 contribution to the photoconductivity spectra of Cr-doped SI GaAs. The optical ionisation energy with respect to the conduction band and the Frank-Condon parameter of Cr2+ centres are obtained from the experimental results.

Polycrystalline samples of copper sulphide having a predominantly tetragonal phase have been investigated. The thermal activation energy of the electric conductivity Delta Ea=0.15 eV associated with the activation energy of an acceptor level has been determined. Low-temperature photoconductivity has been observed for the first time. The photoconductivity spectra measured at 80-120K reveal an appreciable surface recombination rate. From the analysis of these spectra, the minority carrier diffusion length (3.3*10-5-2.5*10-4 cm) and the possible lower limit of the band gap ( Delta Eg approximately=1.2 eV) have been evaluated.

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