Recovering near-band-edge ultraviolet responses in a wide-bandgap oxide with dipole-forbidden bandgap transition

Abstract

High-density SnO2 nanobelts were synthesized on p-Si substrate to form a SnO2 nanobelts/p-Si heterojunction photodiode. The photodiode shows a rectification characteristic in current–voltage measurements and exhibits an ultraviolet peak responsivity with an ultraviolet–visible rejection ratio (R395 nm/R550 nm) of two orders of magnitude. The peak responsivity is located at around 395 nm (3.14 eV), much smaller than optical absorption edge of bulk SnO2 (∼344 nm, 3.6 eV). A strong ultraviolet peak from SnO2 nanobelts at ∼400 nm was observed in the photoluminescence spectrum, indicating that the dipole-forbidden rule of bulk SnO2 is broken for the nanostructural counterparts. First-principles calculations suggest that surface state in nanostructure plays a key role in breaking dipole forbidden rule and realizing ultraviolet peak responsivity.