Measurement of Minority Carrier Diffusion Lengths in Core-Shell GaAs NW p-n Junctions

Abstract

Abstract Body: Core-shell semiconductor nanowires (NWs) are an attractive alternative to planar devices for multiple applications, including field-effect transistors, photovoltaic devices, light-emitting diodes, and lasers. The core-shell radial junction structure enables electron- or photo-induced electron-hole pairs (EHPs) to be collected with shorter diffusion lengths due to the small NW diameter. Furthermore, the collection of the EHPs inside the core is free from surface recombination, potentially improving the energy harvesting efficiency. Electron-induced-beam current (EBIC) measurement is a complementary technique in situ in a scanning electron microscope (SEM), collecting excess carriers in a biased diode as a function of beam position and accelerating voltage. In this talk, we will present the analysis of carrier diffusion properties in unprocessed, free standing core-shell GaAs NW diodes. The carrier kinetics in both the n-type core and the p-type shell were determined by analyzing radial EBIC profiles as a function of beam energy. These profiles are highly sensitive to changes in depletion widths and minority carrier diffusion lengths due to geometric effects. Combined with Monte Carlo simulations, they permitted measurement of the n-type core, minority carrier diffusion length, as well as the depletion widths as a function of radial direction. A relatively short minority carrier diffusion length (50 nm) found near {112}B surface facets can be attributed to bulk point defects originating from low-temperature growth (400 °C). Depletion widths were found to be smaller in B directions than in A, likely due to different dopant corporation efficiencies of Te and Zn in the core and the shell, respectively, and to the very thin shell on the {112}B surfaces.