Thermal mismatch stress relaxation via lateral epitaxy in selectively grown GaN structures

A reduction in the dislocation density of 10(4)-10(5) cm(-2) has been achie ved via lateral epitaxial overgrowth (LEO) of GaN films selectively grown f rom stripes etched in SiO2 masks deposited on GaN/AlN/6H-SiC(0001) heterost ructures. The magnitudes and distribution of stresses generated in the LEO GaN layer and the SiO2, due primarily to differences in the coefficients of thermal expansion, were modeled using finite element (FE) analysis. These calculations showed that localized compressive stress fields of approximate to 3 GPa occurred at the edges of the LEO GaN in the vicinity of the GaN/S iO2 interface. Localized compression along the GaN substrate/SiO2 interface and tension along the [0001] direction were responsible for the change in shape of the SiO2 stripes from rectangular with flat sides to an airfoil sh ape with curved sides. The FE calculations also revealed that an increase i n the width of the LEO GaN regions over the SiO2 or the reduction in the se paration between the GaN stripes (all other dimensions being fixed) resulte d in a slight reduction in the compressive stresses along the LEO GaN/SiO2 interface and an increase in the compressive stress along [0001]. An increa se in the shear stress, at the corners of the LEO GaN near the LEO GaN/SiO2 interface, with an increase in the width of the LEO GaN region were also i ndicated. (C) 1999 American Institute of Physics. [S0003-6951(99)02715-1].