Local structures of nanocrystalline GaN studied by XAFS

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 78 and 300 K. For the first nearest neighbor coordination shell of Ga-N, the average bond length R (0.194 nm), coordination number N (4.0), t hermal disorder sigma (T) (0.0052 nm) and static disorder sigma (S) (0.0007 nm) are nearly independent of the measured temperature and crystalline sta te. This indicates that the Ga-N covalent bond is much stronger, and the 4 nitrogen atoms in first nearest neighbor around Ga atoms keep the tetrahedr al structure (Td). For the second nearest neighbor coordination shell of Ga -Ga, their bond lengths are about 0.318 nm. However, the sigma (S) (0.0057 nm) of nanocrystalline GaN is 0.0047 nm larger than that of crystalline GaN (0.001 nm), and the sigma (T) of nanocrystalline is 0.0053 nm and 0.0085 n m at the temperature of 78 and 300 K, respectively. The result indicates th at the difference of local structure around Ga atoms between nanocrystallin e and crystalline GaN occurs mainly at the Ga-Ga second nearest-neighbor co ordination shell. The reason is explained as the local lattice distortion a nd unsaturated surface atoms existing in nanocrystalline GaN.