Photovoltaic effect in the impurity absorption region of Si-structures with blocked impurity conductivity

A study is made of the field dependence of the photoconductivity in two-lay er Si:Sb- and Si:B-structures with blocked impurity-band conductivity and d ifferent thicknesses of the undoped (blocking) layer. The impurity concentr ation in the doped (active) layer was approximate to 10(18) cm(-3). Measure ments were made at temperatures T = 4-15 K for high (Phi similar to 10(16) photons/cm(2) . s) and low (Phi < 10(14) photons/cm(2) . s) incident photon fluxes. A photovoltaic effect is observed in the Si:B structures with a th in (3 mu m) blocking layer. It is found that a photovoltage develops for ph otons with energies exceeding the ionization energy of boron and its magnit ude is independent of the photoexcitation intensity (for Phi > 10(13) photo ns/cm(2) . s) and, in the limit of low temperatures, it is close to the act ivation energy epsilon(3) for jump conductivity in the active layer. The ph otovoltaic effect is explained by ballistic transit of the blocking layer b y holes emitted from the contact which are then cooled in the active layer, as well as by the presence of a potential barrier approximate to epsilon(3 ) between the active and blocking layers. These factors are taken into acco unt in a model for describing the major features of the dependence of the p hotovoltage on temperature and on the photon intensity and energy. (C) 1999 American Institute of Physics. [S1063-7826(99)01604-X].