Optical properties of Be-doped GaAs nanowires on Si substrate grown by a catalyst-free molecular beam epitaxy vapor–liquid–solid method

The effect of Be doping on the crystal structure and the optical properties of catalyst-free Be-doped GaAs nanowires (NWs) grown on a (111) Si substrate were investigated by scanning transmission electron microscopy (STEM), X-ray diffraction (XRD) analysis, and photoreflectance (PR) and photoluminescence (PL) techniques. Be-doped NWs sample showed a striped pattern in STEM images. Owing to a high arsenic flux under the growth condition, the sample did not have a wurtzite but a zinc-blend (ZB) structure, and the observed striped pattern in STEM images suggests the presence of twin boundaries and stacking faults. The bandgap energy of the Be-doped NWs was lower than that of the nondoped NWs sample in the entire temperature range. In addition, the deviation from the conventional Varshni curve was found to be large in the low-temperature region. However, this is well explained by considering the strong electron-phonon interaction and high average phonon temperature. Therefore, we concluded that the induced strain increased the linear thermal expansion coefficient. This is because the Be atom has a smaller covalent radius than the Ga and As atoms. (C) 2014 The Japan Society of Applied Physics