Influence of N 2 gas pressure on the structural properties of sputter-deposited GaN thin films

GaN thin films were deposited on Si (100) substrates at room temperature by RF magnetron sputtering of a GaN target in a pure N 2 gas whose pressure ranged between 7 and 50 mTorr. The influence of N 2 gas pressure on the structural properties of the deposited GaN films was systematically investigated. The crystalline structure in the GaN films changed from wurtzite to zinc-blende as the N 2 gas pressure was reduced from 50 to 7 mTorr. The observed change in crystalline structure was found to correlate strongly with the changes in the microstructure, surface topography, and internal stress of the GaN films. The microstructure of the GaN films changed from a voided columnar structure having a rough surface to an extremely condensed structure with a very smooth surface morphology as the N 2 gas pressure was decreased. The internal stress of the GaN films was slightly tensile (∼0.34 GPa) at 50 mTorr and became increasingly compressive upon decreasing the N 2 gas pressure, reaching a value of ∼3.08 GPa at 7 mTorr. The above experimental results show that the N 2 gas pressure plays a crucial role in determining the crystalline structure, microstructure, surface topography, and internal stress of the sputter-deposited GaN films.