2D free-standing Ge-doped ZnO: excellent electron-emitter and excitation-power-dependent photoluminescence redshift

Abstract

Two-dimensional (2D) free-standing Ge-doped ZnO nanostructures were synthesized on graphite substrate. A single nanosheet composed of amounts of nanograins with size of ∼20 nm exhibits excellent field electron emission capability that can deliver a current as large as 30 mA cm⁻² at E = 9.0 V μm⁻¹. The amazing performance originates from the high electron conductivity owing to Ge doping, as well as the enriched emitting spots on the surface of the structure. Additionally, we observed the temperature- and excited-power-dependent redshift of photoluminescence (PL) in the temperature range of 77–300 K, which was attributed to the local thermal effect driven nonradioactive enhancement. The rich defect and impurity levels result in alternative recombination mechanisms in the temperature range.