Optical third-harmonic investigations of gallium nitride nucleation layers on sapphire

The magnitude of the chiXXXX(3) element of the third-order optical susceptibility was measured in a series of wurtzite phase GaN nucleation layers (450 A) deposited on (00.1) sapphire at 540 C and annealed to various temperatures up to 1050 C. The nonlinear optical response exhibited a significant increase in films that were annealed to temperatures in the range of 1015 to 1050 C. In addition, the correlation between the magnitude of chiXXXX(3) with both the maximum value of the linear absorbance gradient and the residual homogeneous strain in the overlayer suggests that variations in the crystalline content of the film and the bonding distance between the Ga and N atoms are primary factors in determining the third-order nonlinearity in GaN. (Author)