Current-Voltage Characteristics and Photovoltaic Effect in VO₂/GaN Heterostructures

Vanadium dioxide (VO2) films were prepared on the n-GaN layer at 600 ^◦C and oxygen partial pressure of 10–20 mTorr using pulsed laser deposition. The VO2 films displayed flat surfaces with a roughness of 1.9–2.1 nm, and they were hetero-epitaxy ones with the (200) orientation on n-GaN (0002). With the increase of the temperature, the resistance of the samples exhibited metal-insulator transition behaviors with a resistance change of ∼10⁴ times at TMI of ∼350 K. Current–voltage characteristics indicated that VO2/n-GaN heterojunctions correspond to semiconductor/semiconductor junctions displaying a rectification ratio of ∼100 below TMI, whereas they were metal/semiconductor junctions with a rectification ratio of 3–4 above TMI. When UV light was illuminated, VO2/n-GaN heterostructures clearly showed the photovoltaic effect and photocurrent switching behavior. The VO2/n-GaN heterostructure made at10 mTorr had a potential barrier of ∼1.07 eV, which was estimated from capacitance–voltage measurement. This study shows that the metal-insulator transition behavior can modify the interfacial properties of the VO2/n-GaN heterostructure.