An ion beam technique for real-time measurement of two-dimensional islandsduring epitaxial growth

In this paper, we describe a technique for real-time measurement of two-dim ensional (2D) islands during molecular beam epitaxy. using GaAs(001) growth as the test case. In this technique, an ion beam impinges at a glancing an gle relative to the sample surface, and the specularly scattered ion curren t is measured. The current is a quantitative probe of surface defects, e.g. , adatoms and step edges, which interrupt the locally flat surface needed f or a specular reflection. Nucleation is detected during the early stages of GaAs growth when the measured adatom density drops below the expected valu e, because of adatom self-shadowing in 2D nuclei. After deposition, there i s a relatively fast current recovery-related to adatom diffusion-combined w ith a much slower recovery-explained by a decrease in step-edge density as the 2D island density decreases. Good fits to the recovery data were obtain ed by assuming power-law island coarsening. (C) 1999 Published by Elsevier Science B.V. All rights reserved.