Photovoltaic and thermal effects at PbTe $p$–$n$ junction under CO$_2$ laser irradiation

In this work, two effects appeared in PbTe $p$–$n$ junctions under long-wave irradiation by CO$_2$ laser were investigated. The first effect was created by the optical absorption of long-wave photons in PbTe and caused by its photovoltaic effect. The mechanism of photoeffect is connected with the formation of electron–hole pairs by two-photon processes of absorption and separation of pairs at the $p$–$n$ junction. The second novel effect is related to the heating process and the formation of temperature difference at the $p$–$n$ junction. The main feature of PbTe semiconductor is a strong temperature dependence of static dielectric constant $\varepsilon$. In this case, for PbTe $p$–$n$ junction it was created a barrier pyroelectric effect. PbTe $p$–$n$ junctions were fabricated employing indium donor diffusion into PbTe single crystals grown by the Chochrasky technique. Current–voltage and capacitance– voltage characteristics have been measured over a wide temperature range. The dark saturation current density was $\sim$10$^{-7}$ A/cm$^2$ at $T$ = 100 K. Two methods were used. The short-pulsed CO$_2$ laser light (with a pulse duration of 150 ns) across the PbTe $p$–$n$ junction was used for the investigation of the photovoltaic effect. The continuous irradiation of CO$_2$ was used for the investigation of the thermal effect and caused by its barrier pyroelectric effect (BPE). These two effects were investigated over the 40–150 K temperature range.