Coarsening and slope selection during crystal growth and etching of Ge(001)

The evolution of surface morphology during low temperature crystal growth by molecular beam epitaxy and etching by low-energy ions is characterized by in-situ scanning tunneling microscopy. Epitaxial growth of Ge(001) at low temperatures in the vicinity of 155°C produces a pattern of growth mounds while etching at temperatures near 270°C produces a pattern of low aspect ratio pits. The characteristic in-plane length scale of the surface roughness d increase with a power law dependence on time but the exponent depends on temperature and process. Prior to the onset of amorphous growth, the amplitude of the surface roughness G ^1/2 (d/2) increases more rapidly than d; i.e. the slope of the sides of the growth mounds increases with time. By contrast, the ratio of G ^1/2 (d/2) to d remains nearly constant during ion etching for a wide range of etching times.