Optical studies of wrapgated InP nanowires

Abstract: This thesis describes optical spectroscopy on III-V semiconductor InP nanowires (NW) with a transparent indium-tin-oxide (ITO) gate electrode. The NWs are arranged both as vertical arrays with a wrap all around gate and as single lateral NWs with an omega-shaped gate for increased electrostatic effect. The transparent ITO gate allows optical access with probing lasers in a 4 K He-cryostat while controlling the electrostatic environment with the gate. A coldfinger is constructed to provide easy access when connecting the samples in the cryostat. Photoluminescence (PL) spectroscopy is used to investigate different effects in the NW. A large blueshift (110 meV) in peak energy is seen with increasing excitation power in p-doped samples but only a small shift of 10 meV is seen in n-doped. A model is proposed where this is explained with statefilling and the effective mass being different in the conduction band compared to the valence band. A model by Chia and LaPierre is implemented and expanded to gate bias. It uses density of interface traps ($D_{it}$) to explain how the band bending and depletion in the NW changes with radius, surface defects and bias.