Low- and high-density InAs nanowires on Si(001) and their Raman imaging

摘要

Micro-Raman imaging along with other techniques are applied to study the morphology, structure and crystalline quality of various types of InAs nanowires (NWs). The NWs of low and high densities are formed using metal organic vapor phase epitaxy. Raman mapping is effectively used as a local probe to gain information about the structure and crystalline quality of low-density NWs where the conventional characterization techniques are not very useful. However, for high-density NWs, the image and crystalline quality obtained from the LO phonon strongly corroborate with scanning electron microscopy and x-ray diffraction (XRD) results, respectively. These low-density (10~4 cm~(-2)) and high-density (10~8 cm~(-2)) NWs are grown on Si(001) under various growth conditions such as catalyst-assisted and catalyst-free growth, growth on native oxide-covered and oxide-cleaned Si, grooved Si surfaces and also varying the Ⅴ/Ⅲ ratio and growth temperature. NWs (1 μm long and 50-100 nm wide) with high density and tapered NWs (50-80 μm long and 200-500 nm wide at the tip) with low density are formed under different growth conditions. The growth of hillock- and wire-like structures is observed under the same growth condition. Raman, XRD, scanning electron microscopy and atomic force microscopy analyses confirm that the hillocks are grown along the (001) direction, whereas the wires are grown along [110] directions in the plane of Si(001). Furthermore, the Raman analysis of these NWs confirms that the smaller NWs have much better crystalline quality (half-width of LO phonon frequency ～6 cm~(-1)) compared to the larger NWs (half-width of LO phonon frequency ～15 cm~(-1)) although both NWs are oriented with the Si(001) surface.