Influence of substrate temperature on the electrical and photovoltaic properties of V2O5 modified n-Ge heterojunction

Abstract

Electrical and photovoltaic properties of V₂O₅/n-Ge heterojunction were realized by the deposition of V₂O₅ thin films at different substrate temperatures (room temperature (RT), T_S = 150 °C and 250 °C). Optical properties of V₂O₅ thin films were analysed and direct allowed transitions are found most probable. Infrared measurements of V₂O₅ thin films reveal vibrational bands which confirms the V=O and V–O–V bonds. The shift of these bands with increasing substrate temperature suggests variation in bond lengths which might be due to strain effects in V₂O₅ thin films. X-ray diffraction studies were also performed for V₂O₅/n-Ge heterojunctions which indicates the amorphous nature of V₂O₅ thin films for V₂O₅(RT)/n-Ge heterojunction and crystallinity of the films found to be increased by increasing the substrate temperature. Current-voltage properties of V₂O₅/n-Ge heterojunctions at different substrate temperatures were studied and found variations in barrier properties of the devices with an increase in substrate temperature. Explored forward bias current conduction mechanisms of heterojunctions reveal trap charge limited current conduction is the dominant conduction at moderately high bias potential particularly for V₂O₅(T_S = 150 °C and 250 °C)/n-Ge heterojunctions. Photovoltaic properties of V₂O₅/n-Ge heterojunctions indicate notable responsivity of V₂O₅ thin films under illumination (100 mW/cm²) at increased substrate temperature. The sensitivity of the V₂O₅(150 °C)/n-Ge heterojunction was found to be maximum than other heterojunctions whereas the photoresponsivity and specific detectivity of the heterojunction shows significant variation with bias and substrate temperature. The electrical and photoresponsive properties of V₂O₅ thin films on n-Ge substrate altered effectively by substrate temperature of V₂O₅ thin films. This triggers the variation of these properties by changing the conductivity of thin films with doping or post annealing conditions.