Photovoltaic phenomena in inhomogeneous semiconductors

The photovoltaic phenomena in inhomogeneous semiconductors are discussed here. (i) The Rooesbroeck potential is generalised and the formulae defining the Tauc bulk photovoltaic effect (BPV), in semiconductors with position-dependent doping, are derived. (ii) The domain of the inhomogeneities is expanded, and besides doping the cases of position-dependent energy gap EG and mobilities in the presence of temperature gradient are described. Thus a new thermo-photovoltaic effect is revealed. (iii) The equations describing the BPV potential distribution in the case of point illumination are derived. Using the Green function formalism the equations are obtained, which give a base to examine the inhomogeneities especially of resistivity distribution. (iv) The method of images is used to calculate the BPV potential distribution. The potential distributions in rectangular plates and circular slices are presented. (v) The results of photovoltaic measurements carried out on a sample with temperature gradient are presented, giving an experimental confirmation of the thermophotovoltaic effect. Application of BPV to determine experimentally resistivity distribution is demonstrated. (vi) The theory and measurements of the bulk photoelectromagnetic effect (BPEM) taking place in an inhomogeneous semiconductor exposed to magnetic field are presented.