Quantum confinement effect of nanocrystalline GaN films prepared by pulsed-laser ablation under various Ar pressures

Pulsed-laser deposition (PLD) was performed under various Ar pressures to prepare nanocrystalline GaN films without substrate heating or any post-annealing treatment. The X-ray diffraction (XRD) pattern and selected area electron diffraction indicated that the deposited films were hexagonal GaN with wurtzite structure. High-resolution transmission electron microscopic observation revealed that the particles in GaN films deposited in Ar ambient gas below 50 Pa were smaller than the exciton Bohr radius of GaN (11 nm). Large blueshifts in optical bandgap of the films deposited at lower Ar pressures were observed, indicating strong quantum confinement effects in small GaN particles.