Low-temperature GaN microcrystal formation at 600 degrees C was demonstrated on As-terminated Si (100) in the form of periodic arrays using droplet epitaxy. In all 100 eV Ga ions were irradiated with 2 mu m spacing onto As-terininated Si (100) to create reactive nucleation sites. Subsequently Ga atoms were supplied to the surface. The deposited Ga atoms from an effusion cell migrated on the surface and were trapped at the nucleation sites to form Ga droplets. Excited atomic nitrogen was then supplied to the surface to form GaN microcrystals. SEM observations indicated that the GaN microcrystals with 0.8 mu m diameter were present every 2 mu m periodically. Band edge emission was observed from the GaN microcrystals by cathode luminescence. (c) 2005 Elsevier B.V. All rights reserved.