Ellipsometry for III–V epitaxial growth diagnostics

Abstract

Spectroscopic ellipsometry’s (SE’s) strength as an in situ semiconductor crystal growth process diagnostic lies in the fact that the material’s dielectric properties (pseudodielectric functions) are dependent upon temperature and alloy composition. These dependencies can be exploited to monitor and control epitaxial growth in real time. This article reviews several aspects of growth and control of III–V semiconductors grown at Arizona State University by molecular beam epitaxy (MBE) using SE. Chamber and manipulator design considerations for implementing SE on a MBE and a gas source MBE with substrate rotation will first be discussed. A commercially available ‘‘ellipsometer-ready’’ MBE system will then be described. It will then be shown that a MBE process can be established without conventional analysis tools such as reflection high energy electron diffraction. Measurement and control of substrate temperature by SE will be shown. This is possible by using the temperature-dependent pseudodielectric functions for GaAs and AlGaAs which we have measured. Calibration of MBE growth will be discussed including in situ measurement of oxide desorption, V/III flux ratio, growth rate, and alloy composition measurements. Tracking the growth of the epitaxial layer provides information on thickness, alloy composition, and surface roughness. Algorithms for deconvoluting these effects from the data will be discussed. Finally, examples of structures used in optoelectronic devices will be presented including quantum well thickness control and microcavity laser device growth.