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

Abstract

A study is made of the field dependence of the photoconductivity in two-layer Si:Sb-and Si:Bstructures with blocked impurity-band conductivity and different thicknesses of the undoped (blocking) layer. The impurity concentration in the doped (active) layer was ≈10¹⁸ cm⁻³. Measurements were made at temperatures T=4–15 K for high (Φ∼10¹⁶ photons/cm² · s) and low (Φ<10¹⁴ photons/cm² · s) incident photon fluxes. A photovoltaic effect is observed in the Si:B structures with a thin (3 µm) blocking layer. It is found that a photovoltage develops for photons with energies exceeding the ionization energy of boron and its magnitude is independent of the photoexcitation intensity (for Φ>10¹³ photons/cm² · s) and, in the limit of low temperatures, it is close to the activation energy ɛ ₃ for jump conductivity in the active layer. The photovoltaic effect is explained by ballistic transit of the blocking layer by holes emitted from the contact which are then cooled in the active layer, as well as by the presence of a potential barrier ≈ɛ ₃ between the active and blocking layers. These factors are taken into account in a model for describing the major features of the dependence of the photovoltage on temperature and on the photon intensity and energy.