MORPHOLOGICAL INSTABILITY OF A TERRACE EDGE DURING STEP-FLOW GROWTH

We consider the possibility that monoatomic terrace edges undergo a morphological instability during epitaxial Istep-flowR growth. A linear stability analysis predicts that such an instability can occur, but only when the energy barriers to adatom attachment to steps differ for adatoms that approach a step from opposite directions. The instability is diffusional in origin and manifests itself as a distinct waviness or meandering of the terrace edges as they propagate across the crystal. Our results, presented in the form of a morphological phase diagram, show that single-crystal growth on a vicinal surface can pass from stable step flow to unstable step flow to two-dimensional island nucleation and spreading as one increases the incident flux in a molecular-beam-epitaxy experiment at elevated temperature. The instability we predict should be readily distinguishable from simple thermal fluctuations. © 1990 The American Physical Society.