Lateral overgrowth mechanisms and microstructural characteristics of bulk-like GaN layers grown by sublimation method

The selective overgrowth method has been used to grow bulk-like GaN layers by sublimation method. Si and SiO2, which have a different evaporation rate , thermal conductivity, and thermal expansion coefficient, have been chosen as mask materials. The effect due to the reduction of dislocation density with different mask materials has been discussed. The lateral growth rates strongly depend on the direction of the mask stripe. For the stripe windows aligned in GaN[1 (1) over bar 00] direction, the lateral growth rate is ap proximately four times higher than with stripe direction in GaN[11 (2) over bar 0]. The microstructure of selectively regrown GaN has been investigate d by transmission electron microscopy, scanning electron microscopy, and ca thodoluminescence to understand the lateral growth mechanisms in sublimatio n. The threading dislocations in the region of laterally regrown GaN are ex tended in two different ways. First, the threading dislocations are perpend icularly propagated into the top surface in the window region. In this case , the density of the threading dislocation is about 10(9) cm(-2) within the window regions of the mask and is reduced to 10(6) cm(-2) in the lateral o vergrowth region of the mask due to termination of further propagation of d islocation by the mask. Second, the direction of propagation of dislocation s is changed parallel to the c plane in laterally overgrown GaN, and finall y, it changes in the direction perpendicular to the c plane in the middle r egion of the mask. (C) 1999 American Institute of Physics. [S0021-8979(99)0 6603-7].