Photothermovoltaic Effect in p-Si−n-(Si₂)_{1 –x–y}(Ge₂)_x(ZnSe)_y Structure

A promising direction in photovoltaic and heat power engineering is the development of highly efficient photothermovoltaic (РTV) systems to convert the thermal energy of heated bodies into electrical energy. They have important advantages over other thermal power devices. It is known that heating negatively affects the operation of many semiconductor devices, but it increases the efficiency of photothermovoltaic element. The process of the appearance of voltage and electric current in the p-Si–n-(Si₂)_{1 – x – y} (Ge₂)_x(ZnSe)_y structure during uniform heating both in the dark and in light was studied in this work. The uniform heating of the p‑Si–n-(Si₂)_{1 – x – y}(Ge₂)_x(ZnSe)_y heterostructure both in the dark by thermal heating and photoheating and in light by solar radiation generated an electric current and a potential difference. The dark current generated by photoheating in the studied temperature range has a greater value of three orders of magnitude than in the case of thermal heating. However, the potential difference generated by photoheating slightly decreases with increasing temperature, but its value is almost two orders of magnitude greater than in the case of thermal heating. There is also a slight decrease in the photocurrent and potential difference at increasing temperature. Since the composition of the substrate-film intermediate region changes continuously from Si to the p-Si–n-(Si₂)_{1 – x – y}(Ge₂)_x(ZnSe)_y epitaxial film, a graded-gap layer with a smoothly varying composition prevents breaks in the energy zones of the p–n structure. Due to the variability in the intermediate region, an energy barrier arises, mainly for holes, which contributes to the appearance of an additional separating field, which is determined by the gradient of the band gap of this layer. Therefore, the hole current in this structure that is caused by photothermally generated electron-hole pairs can be significant up to higher temperatures. The low efficiency of the studied structure is clearly associated with the recombination of the main parts of the photothermally generated charge carriers.