Passivation efficacy study of Al2O3dielectric on self-catalyzed molecular beam epitaxially grown GaAs1-xSbxnanowires.

This work evaluates the passivation efficacy of thermal atomic layer deposited (ALD) Al2O3dielectric layer on self-catalyzed GaAs1-xSbxnanowires (NWs) grown using molecular beam epitaxy. A detailed assessment of surface chemical composition and optical properties of Al2O3passivated NWs with and without prior sulfur treatment were studied and compared to as-grown samples using x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature photoluminescence (PL) spectroscopy. The XPS measurements reveal that prior sulfur treatment followed by Al2O3ALD deposition abates III-V native oxides from the NW surface. However, the degradation in 4K-PL intensity by an order of magnitude observed for NWs with Al2O3shell layer compared to the as-grown NWs, irrespective of prior sulfur treatment, suggests the formation of defect states at the NW/dielectric interface contributing to non-radiative recombination centers. This is corroborated by the Raman spectral broadening of LO and TO Raman modes, increased background scattering, and redshift observed for Al2O3deposited NWs relative to the as-grown. Thus, our work seems to indicate the unsuitability of ALD deposited Al2O3as a passivation layer for GaAsSb NWs.