Twin defects were analyzed in nanowires as thin as 100 to 400nm and tetrahedral structures as small as 1.0μm, selectively grown onto GaAs(111)B substrates by means of metalorganic vapour-phase epitaxy within a SiO2 mask window. Attention was focussed upon a correlation between the twins and GaAs(111)B surface reconstruction. It was confirmed that the shape of GaAs crystals, selectively grown onto GaAs(111)B substrate, from hexagonal nanowires to truncated tetrahedra when the size of the mask opening was increased from 100 to 1000nm; under the same growth conditions. The shape also changed from tetrahedral to hexagonal with decreasing growth temperature (600 to 800C) and with increasing arsine (AsH3) partial pressure (1.0 x 10−4 to 5.0 x 10−4atm). Rotational twins around the <111> axis were found, in the tetrahedral, by means of transmission electron microscopy and scanning electron microscopic observations. The probability of twins developing in the tetrahedra increased with decreasing mask opening size, with decreasing growth temperature and with increasing AsH3 partial pressure. The transmission electron microscopic study also revealed the existence of a high density of rotational twins in the nanowires. Their density increased with decreasing nanowire diameter, and suggested a correlation between the twins and the shape/size of GaAs crystals. By analyzing the relationship between twin development and MOVPE conditions, it was found that the shape change of GaAs crystals on GaAs(111)B, and the formation of twins, coincided well with a transition in GaAs surface reconstruction between the (2 x 2) and (√19 x √19) structures.

Analysis of Twin Defects in GaAs Nanowires and Tetrahedra and their Correlation to GaAs(111)B Surface Reconstructions in Selective-Area Metal Organic Vapour-Phase Epitaxy. H.Yoshida, K.Ikejiri, T.Sato, S.Hara, K.Hiruma, J.Motohisa, T.Fukui: Journal of Crystal Growth, 2009, 312[1], 52-7