Freestanding GaAs Nanowires with a Controlled Diameter and Their Optical Properties with the Radial Quantum-confinement Effect


Guoquiang Zhang, Kouta Tateno, Haruki Sanada, and Hideki Gotoh
Optical Science Laboratory

 Semiconductor nanowires (NWs) have attracted considerable attention owing to the interesting fundamental properties of such low-dimensional systems and the exciting prospects of utilizing these materials in nanotechnology-enabled electronic and photonic applications. NWs are expected to provide the building blocks with which to form new nanostructures and realize novel 1-dimensional structures. To explore the potentially unique applications of these freestanding NW building blocks, we synthesized freestanding GaAs NWs with a controlled diameter and studied their optical properties with the radial quantum-confinement effect.
 The NW growth was undertaken in a metalorganic vapor phase epitaxy system and Au nanoparticles were used to catalyze the NW growth via the vapor-liquid-solid (VLS) mode [1]. We controlled the diameter of the GaAs NWs by using size-selective Au colloidal particles with nominal diameters of 5, 10, 20, 40, and 60 nm [2]. We characterized the structure and diameter of the NWs using transmission electron microscopy (see Fig. 1). We successfully controlled the NWs with very few stacking faults by growing them at a very low temperature. We studied their optical properties by employing micro-photoluminescence (PL) at 3.6 K [3]. Figure 2(a) shows PL spectra from individual NWs of different Au particle sizes. PL peak energies clearly exhibit the blue shift with decreasing Au particle size due to the radial quantum-confinement effect [2]. We analyzed the absorption and emission polarization characteristics of these NWs and found large anisotropies between polarization resolved PL spectra (see Fig. 2(b)). These results suggest that both the dielectric constant contrast and the quantum-confinement effect have to be considered [2]. This work opens the way to investigating size-related optical phenomena in bare GaAs quantum wires, and provides more opportunities for the study of one-dimensional quantum physics using freestanding NWs.

[1] G. Zhang et al., J. Appl. Phys. 103 (2008) 014301.
[2] G. Zhang et al., Appl. Phys. Lett. 95 (2009) 123104.
[3] G. Zhang et al., Jpn. J. Appl. Phys. 49 (2010) 015001.

Fig. 1. TEM images of free standing GaAs NWs. (a) Single
NW. (b) and (c) high-magnification images of the
segments near the middle and tip in (a). The inset in
(b) is the corresponding diffraction pattern, which
indicates a zinc-blende structure. (d) HRTEM image
near the NW side. (e) Images for Au particles with
different diameters.
Fig. 2. (a) PL spectra of single GaAs NWs grown
using Au particles with three nominal
diameters. (b) Polarization resolved PL
spectra. The red broken line indicates the
free excitonic PL energy in bulk GaAs.

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