From Thermodynamics to Quantum Wires: A Review of Reflection High-Energy Electron Diffraction

Abstract

The built-in staircase of steps on a vicinal surface has been used by Petroff and coworkers as a template for the growth of quantum wires. The limits of this technique depend upon the degree to which the steps are ordered before and during growth and on the extent of step meandering. Here we review those aspects of reflection high energy electron diffraction (RHEED) that allow characterization of these staircase steps during growth by molecular beam epitaxy. First we describe Henzler’s methods of measuring the surface step distribution. We use Lagally’s criterion to give an operational measurement of the transfer width of a RHEED instrument. We show that in the direction of the incident beam, coherent diffraction over distances as large as 8000 A is detected. Simple one-dimensional models of terrace length disorder are considered to show the sensitivity of the measured pattern. The appropriate correlation functions of surface disorder are described. By directing the beam perpendicular and parallel to the staircase, we also examine the kink density. Differences that depend upon the two types of step termination possible on a zincblende structure are observed. Recent work of Bartelt and Einstein on scaling is described. The main difficulties are that to apply equilibrium arguments, sufficient temperature and flux stability is required to balance growth and sublimation. A second difficulty is that trace impurities can pin steps during growth.