Growth evolution of surface nanowires and large anisotropy of conductivity on MgZnO/ZnO quantum wells based on M-nonpolar (10−10) ZnO

Abstract

Articles you may be interested inMgZnO/ZnO quantum well nanowire heterostructures with large confinement energies Self-organized surface nanowires were formed on M-nonpolar ͑10− 10͒ ZnO homoepitaxial layer surfaces. High-resolution transmittance electron microscopy showed that the surface nanowires possessed a flat plateau at the top and a side facet with constant step spacing at the atomic scale. In and ex situ observations of layer growth revealed that anisotropic islands appeared after growing two-dimensional surfaces and that these gradually changed to nanowire structures with increasing layer thickness. Their growth origin, identified from theoretical parameter fittings based on a step-edge barrier model, was close to that of O-polar ZnO growth. A large difference in electron transport was clearly observed in Mg 0.12 Zn 0.88 O / ZnO quantum wells ͑QWs͒. Transport anisotropy correlated strongly with the surface morphology and with the structural quality of QWs, as confirmed by polarized photoluminescent spectroscopy. Finally, as a possible mechanism of anisotropic electron transport, we suggest that the electron motion perpendicular to the nanowire arrays was strongly restricted due to a potential barrier caused by an interface roughness of the surface nanowires.

Hydrothermal growth of ZnO nanorods on a-plane GaN/sapphire template

“…By rotating the samples it was observed that a majority of the nanorods in the present case makes an angle of approximately 301 with respect to the substrate normal. This value is similar to the reported inclination angle of ZnO nanorods grown on r-and m-plane sapphire by metal-organic vapor phase epitaxy and PLD method [18][19][20]. It should be noted, however, that the ZnO nanorods in the present study are inclined to only one side of the substrate normal.…”

“…The common feature of nanorod tilting relative to the substrate normal was noticed in both cases of nanorods. Such offnormal ZnO nanorods/nanowires grown on a-plane GaN buffer layer, m-and r-sapphire substrates and MgO (1 0 0) substrate by vapor phase techniques have been reported [18][19][20]26]. By rotating the samples it was observed that a majority of the nanorods in the present case makes an angle of approximately 301 with respect to the substrate normal.…”

“…Recently the growth of ZnO thin films and nanorods on non-polar or semi-polar GaN has attracted a lot of attention. There have been a number of studies on growth of one-dimensional ZnO nanostructures particularly by chemical vapor transport methods and physical deposition techniques on non-polar substrates [16,[18][19][20]. However, the growths of ZnO nanorods/nanowires on non-polar GaN substrates by hydrothermal technique have been rarely attempted.…”

Growth and structural characterization of intrinsic, acceptor, and donor doped (Mg,Zn)O epilayers via metalorganic vapor phase epitaxy on (1 0 1¯ 0) ZnO substrates

“…In addition to high surface energies on polar planes [24], the variation of adatom mobility and diffusion with different crystallographic directions [25] may facilitate the preference of Volmer-Weber growth mode on the c-plane. Pierce et al [14] and others [16,26] have shown monocrystalline deposition of ZnO on non-polar substrates and indicate the feasibility of step-flow growth on non-polar orientations. The utility of non-polar orientations have been favored for use in optoelectronic devices due to the reduction of internal electric fields, which lead to the quantum confined Stark effect (QCSE) and compromise quantum efficacies with increasing injected carrier density.…”

“…Astute deposition schemes [14] have been used to achieve contiguous epilayers on c-plane ZnO by MOVPE; the realization of Frank-van der Merwe growth mode has often been limited to physical deposition techniques such as pulsed laser deposition [15,16] and molecular beam epitaxy [17][18][19][20] or solution growth [21][22][23]. In addition to high surface energies on polar planes [24], the variation of adatom mobility and diffusion with different crystallographic directions [25] may facilitate the preference of Volmer-Weber growth mode on the c-plane.…”