Photocarrier injection and the I–V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions

Oxide heterojunctions made of p-type La0.8Sr0.2MnO3 (LSMO) and niobium-doped n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current–voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency γ are estimated to be 8.3×1012 cm−2 and 11% at room temperature, respectively. They are improved significantly in a p–i–n junction of LSMO/STO/STO:Nb, where Q/e and γ are 3.0×1013 cm−2 and 27%, respectively.