Surface Photovoltaic Effect and Its Applications to Si Wafers and Monocrystalline Si Solar Cells Diagnostics

Surface photovoltage (SPV) method is presented as a powerfull tool for Si wafers and monocrystalline Si solar cells diagnostics, mainly for minority carrier diffusion length determination. We begin with some basic electrical properties of semiconductor surfaces and basic theory of the effect. Next, the so-called constant SPV method, together with new improved technique called CPV (contactless photovoltage) method are reviewed. Two different experimental arrange-ments for CPV method, with one space charge region (SCR) and with two SCRs are presented and corresponding calculated photovoltage spectra both for wafers and solar cells are compared with experimental data. Also some deformed experimental photovoltage spectra from Si wafers measurements are presented as a manifestation of their disturbed surfaces after slicing and/or surface grinding. A photovoltage (PV) arises whenever light-induced excess charge carriers (electron-hole pairs) are separated within the SCR which exists inside the p-n junction (in the case of a solar cell) or in spontaneously created SCR under a free semiconductor surface. The latter phenomena is called surface photovoltaic effect. This way produced photovoltage is a surface analogue of the well-known volume photovoltage which arises inside solar cells. The method is a well-established contactless technique for the characterization of semiconductors, namely for measurements of the diffusion length of minority carriers in the region of essential light absorption inside solar cells and wafers. During the time, the technique has continuously evolved and newer and better experimental arrangements and tools have emerged. Namely, contactless photovoltage method (CPV) is presented as a generalization of conventional investigation of semiconductor parameters. In contrast to conventional SPV, the CPV is not limited to one SCR existing only in the vicinity of the surface. The CPV theory was derived from basic transport mechanisms in semiconductors. Calculated spectra are then presented for two different experimental arrangements - with one SCR and with two SCRs. In the latter case, the existence of two SCRs causing two signals of opposite sign was taken into account. By fitting the calculated theoretical spectra to experimental data obtained from Si wafers and monocrystalline Si solar cells measurements minority carriers diffusion length was derived. Also some deformed experimental spectra from Si wafers measurements are presented as a manifestation of their disturbed surfaces after slicing and/or surface grinding. At the conclusion some future plans are presented.