Thesis presented March 15, 2017

Abstract:
III-nitride nanostructures have been attracting increasing attention due to their peculiar properties and potential device applications as lighting LEDs. The control and evaluation of the doping in the nanostructures is a crucial, yet a challenging issue. This thesis advances the field by exploring the n and p type doping process of GaN nanowires (NWs) grown by molecular beam epitaxy (MBE). In particular, their electrical properties have been revealed through a multi-technique approach at the single NW level. Firstly, the structural and electrical properties of a series of Si-doped (n-type) GaN NWs have been studied. High resolution energy dispersive X-ray spectroscopy measurements on single NWs have illustrated the achievement of a higher Si incorporation in NWs than in epilayers, and Si segregation at the edge of the NW with the highest doping. Furthermore, direct transport measurements (four probes measurements from 300 K down to 5 K) on single NWs have shown a controlled doping with resistivity from 10² to 10^-3 Ω.cm, and a carrier concentration from 10¹⁷ to 10²⁰ cm^-3. Field effect transistor measurements have evidenced the n-type nature and a high electron mobility of the non-intentionally doped NWs. Secondly, the growth conditions of Mg-doped (p-type) and axial GaN p-n junction NWs have been determined to achieve significant Mg incorporation. Furthermore, the electrical properties of the axial GaN p-n junction NWs, dispersed on SiO₂ and contacted by ITO, have been studied using electron beam induced current (EBIC) technique. EBIC technique revealed the location of the p-n junction and clearly demonstrated its operation under reverse and forward polarization. Moreover, EBIC showed highly resistive p-GaN in accordance with the difficulties to perform direct transport measurements on p-GaN NWs. This original study provides a nanoscale description of the electrical and doping properties of the GaN NWs, facilitating the fabrication of the future GaN nanostructures based devices.

Keywords:
Axial p-N junction, Electron beam induced current, Molecular beam epitaxy, GaN, Nanowires, N and p-Type doping

On-line thesis.