Role of dislocation-free GaN substrates in the growth of indium containing optoelectronic structures by plasma-assisted MBE

Plasma-assisted molecular beam epitaxy (PAMBE) has recently emerged as a viable tool for production of nitride blue-violet laser diodes operating at room temperature in continuous wave mode and high output powers [C. Skierbiszewski, P. Wisniewski, M. Siekacz, P. Perlin, A. Feduniewicz-Zmuda, G. Nowak, I. Grzegory, M. Leszczynski, S. Porowski, Appl. Phys. Lett. 88 (2006) 221108]. The present work reviews the current state of the art in this program as well as discusses its future directions. Two elements are given particular attention: (1) the epitaxial growth in metal-rich conditions, which enables effective lateral diffusion of N adatoms at low growth temperatures and (2) the role of threading dislocations in destabilizing the growth front. Low-temperature growth by PAMBE on dislocation-free GaN substrates is instrumental in achieving high performance of optoelectronic structures. The inherent to this process capability of sustaining two-dimensional step-flow growth mode (with straight and parallel atomic steps) at low growth temperatures opens up the way to the growth of strained multilayer structures with no compositional fluctuations and with flat interfaces.