Photoeffects in Lead Telluride p-n Junctions

Abstract

The direct energy gap in PbTe has been deduced over the range 3.5°≤T≤300°K, from the spectral dependence of short circuit photocurrent in grown p‐n junctions. At temperatures above ∼30°K, the deduced absorption in the depletion region is found to be exponential, with the steepness of the edge dominated by thermal broadening. At lower temperatures, the effects of broadening due to the electric field within the junction depletion region have been observed. A third broadening mechanism is observed at low temperatures. At 5.8°K, this mechanism is of approximately equal strength to the thermal broadening. The energy gap, taken from the photon energy at which the photocurrent has fallen to one‐half its maximum value, at which point the absorption coefficient α=14 cm⁻¹, is given by E_g=0.173+0.485×10⁻³T eV for temperatures 30°<T<250°K. Below ∼10°K, the energy gap has a constant value of 0.185±0.002 eV.