Variation of lattice parameters with growth conditions in GaN

Lattice parameters are measured for GaN samples, grown at different growth temperatures (800 to 1130°C) and in different carrier gases (He, H2). An increase in c and a slight decrease in a with increasing growth rate is found, whereas the growth temperature seems to be of no direct effect. It appears that for an interpretation of the large variation in the lattice parameters in GaN stoichiometry effects are of less importance than lattice defects and foreign impurities.