The Ti-mask selective-area growth (SAG) of GaN nanocolumns was performed at the growth temperature of 900 degrees C, while decreasing the supplied nitrogen flow rate (Q(N2)) from 3.5 to 0.5 sccm. Highly uniform arrays of GaN nanocolumns were demonstrated. At low Q(N2), both the desorption and diffusion of Ga from/on the nitrided Ti mask were accelerated, which sufficiently suppressed the crystal nucleation on the Ti-mask surface, and hence the SAG of the GaN nanocolumns was achieved even when the spacing between the nanocolumns was several hundred nm. The enhancement of Ga desorption with decreasing Q(N2) brought about a reduction in the growth rate of GaN nanocolumns from 1.05 to 0.15 mu m/h. The lateral growth rate of the GaN nanocolumns rapidly increased above the critical Q(N2) value of 1.5 sccm and became 45 nm/h at Q(N2) of 3.5 sccm. For low Q(N2) values less than 1.5 sccm, the lateral growth rate became sufficiently low, approximately 8 nm/h; this contributes to well-controlled SAG of GaN, where the underlying nanomask patterns are well traced. (C) 2008 Elsevier B.V. All rights reserved.