Space charge limited conduction mechanism in GaAsSb nanowires and the effect of in situ annealing in ultra-high vacuum

In this work, the first observation of the space charge limited conduction mechanism (SCLC) in GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxial technique, and the effect of ultra-high vacuum in situ annealing have been investigated. The low onset voltage of the SCLC in the NW configuration has been advantageously exploited to extract trap density and trap distribution in the bandgap of this material system, using simple temperature dependent current–voltage measurements in both the ensemble and single nanowires. In situ annealing in ultra-high vacuum revealed significant reduction in the trap density from 10¹⁶ cm⁻³ in as-grown NWs to a low level of 7 × 10¹⁴ cm⁻³ and confining wider trap distribution to a single trap depth at 0.12 eV. A comparison of current conduction mechanism in the respective single nanowires using conductive atomic force microscopy (C-AFM) further confirms the SCLC mechanism identified in GaAsSb ensemble device to be intrinsic. Higher current observed in current mapping by C-AFM, increased 4 K photoluminescence (PL) intensity along with reduced full-width half maxima and more symmetric PL spectra, and reduced asymmetrical broadening with increased TO/LO mode in room temperature Raman spectra for in situ annealed NWs again attest to effective annihilation of traps leading to the improved optical quality of NWs compared to as-grown NWs. Hence, the I–V–T analysis of the SCLC mechanism has been demonstrated as a simple approach to obtain information on growth induced traps in the NWs. (paper)