Transparent p-CuI/n-BaSnO3−δ heterojunctions with a high rectification ratio

Transparent p-CuI/n-BaSnO3−δ heterojunction diodes were successfully fabricated by the thermal evaporation of a (1 1 1) oriented γ-phase CuI film on top of an epitaxial BaSnO3-δ(0 0 1) film grown by the pulsed laser deposition. Upon the thickness of the CuI film being increased from 30 to 400 nm, the hole carrier density was systematically reduced from 6.0 × 1019 to 1.0 × 1019 cm−3 and the corresponding rectification ratio of the pn diode was proportionally enhanced from ~10 to ~106. An energy band diagram exhibiting the type-II band alignment is proposed to describe the behavior of the heterojunction diode. A shift of a built-in potential caused by the hole carrier density change in the CuI film is attributed to the thickness-dependent rectification ratio. The best performing p-CuI/n-BaSnO3−δ diode exhibited a high current rectification ratio of 6.75 × 105 at ±2 V and an ideality factor of ~1.5.