Dependence of diode behaviour and photoresponse of Ga-doped ZnO (GZO)/p-Si junction on the carrier concentration of GZO layer

Abstract

Ga-doped ZnO (GZO)/p-Si junctions were fabricated by reactive co-sputtering of Zn-GaAs target in Ar–O2 atmosphere. Highly degenerate GZO (carrier concentration ∼1021 cm−3) deposited at 4 % O2 forms non-rectifying contact with p-Si. GZO/p-Si diodes fabricated with moderately doped GZO layers deposited at 5 % O2, having carrier concentration ∼1019 cm−3 display low turn-on voltage (≲ 0.5 V) and ideality factor ≈ 2. Measurement of barrier height by temperature dependent I–V and built-in potential by C–V reveal respective values of (0.74 ± 0.07 eV) and (0.44 ± 0.04 eV), suggesting formation of Schottky type diodes. These diodes display nearly linear I–V characteristics under UV illumination, yielding photoresponsivity ∼1 A/W at ± 1 V. In contrast, GZO/p-Si diodes fabricated with lightly doped (non-degenerate) GZO layers deposited at 6–8 % O2, having carrier concentration ∼1018 cm−3, show higher turn-on voltages (4.5–6.5 V) and ideality factors of 2.5–2.7. I–V and C–V measurements reveal nearly equal values of barrier height and built-in potential, indicating formation of n-p heterojunctions, with near-elimination of conduction band discontinuity. Under UV illumination, I–V characteristics of these GZO/p-Si diodes display non-linear behaviour in forward bias and yield photoresponsivity of ∼0.1 A/W at ±1 V.