Incorporation of Be dopant in GaAs core and core-shell nanowires by molecular beam epitaxy

Effective implementation of doped nanowires (NWs) in nanoscaled devices requires controlled and effective dopant incorporation. The one dimensional configuration of NWs poses a challenge for efficient doping due to the large number of surface states pinning the Fermi level close to the middle of the band gap and thus creating a large depletion layer at the surface. This effectively reduces the effective volume for doping. However, the flexibility of different architectures offered by the NWs, in particular, the core-shell configuration along with different growth mechanisms associated with the core and shell can be strategically used for efficient doping. In this work, the authors report on a catalyst free Ga-assisted approach for the growth of Be-doped GaAs NWs by molecular beam epitaxy. A systematic and a comprehensive study is reported using a variety of characterization techniques to determine the impact of NW configuration, Be cell temperature, and V/III beam equivalent pressure (BEP) ratio individually on doping incorporation in the NWs. Broadening of the photoluminescence spectra in the 1.49-1.51 eV range, as well as the longitudinal optical mode of the corresponding Raman spectra in combination with its red shift that is considered as a signature of higher Be incorporation, was found to occur for the core-shell configuration. Further, a lower V/III BEP ratio has a strong impact on enhancing the dopant incorporation.