GaN and InN Nanowires: Growth and Optoelectronic Properties

Self-assembled GaN and InN nanowires (NWs) were synthesized by radio frequency Plasma-Assisted Molecular Beam Epitaxy (PAMBE) without external catalyst. NWs of micrometers length and diameter in the range of 20–200 nm are fabricated using this method under N-rich conditions. Driving mechanisms of the NW nucleation and the growth are discussed. The NWs have been investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and photoluminescence (PL). Electric and photoelectric measurements on single wire devices have been performed as well. We establish that the dark, Ultraviolet (UV) photo-current and band-edge absorption tails in GaN NWs are strongly dependent on wire diameter. A model of surface Fermi level pinning and Franz-Keldysh effect in carrier depletion region at wire surface were used to explain the observed behaviors. InN NWs show infrared (IR) photoluminescence strongly dependent on the growth parameters. High electron concentration of 10¹⁸ – 10¹⁹ cm⁻³ was evaluated from line shape analysis of PL spectra. The Fermi level pinning at the surface corresponds to a surface accumulation layer. To modify the surface of InN NWs, core-shell InN/GaN NWs were grown. In this paper we focus on the influence of surface effects on the growth and properties of GaN and InN nanowires.