XAFS studies on local structures of nanocrystalline and crystalline GaN

X-ray absorption fine structure (XAFS) was used to investigate the local st ructures around Ga atoms in the hexagonal nanocrystalline and crystalline G aN under 78K and 300K. For the first nearest-neighbor coordination of Ga-N, the average bond length R, coordination N, thermal disorder sigma (T) and structural disorder as of nanocrystalline GaN are similar to those of cryst alline GaN, which are 0. 194nm, 4. 0,0. 0052nm and 0. 0007nm, respectively. When the temperature is elevated from 78K to 300K, the sigma (T) in GaN sa mples increases by lower than 0. 0005nm. It indicates that the Ga-N covalen t bond is much stronger , and is nearly independent of temperature and crys talline state. For the second nearest-neighbor Ga-Ga coordination, the R va lues of the samples are about 0. 318nm; the sigma (s)(0. 0057nm) of nanocry stalline GaN is 0. 0047nm larger than that of crystalline GaN(0. 001nm); th e sigma (T) of Ga-Ga coordination in nanocrystalline GaN are 0. 0053nm, 0. 0085nm for the temperature of 78K and 300K , respectively. This shows that the a, of Ga-Ga coordination is greatly affected by the temperature. The ma jor difference of local structure around Ga atoms between nanocrystalline G aN and crystalline GaN is shown by the relatively large sigma (s) of the Ga -Ga second nearest-neighbor shell in nanocrystalline GaN. The reason may be explained by that there exist larger defects and unsaturated surface atoms in nanocrystalline GaN.