In situ spectroscopic ellipsometry in molecular beam epitaxy

Abstract

Noninvasive, real-time material growth monitoring is becoming increasingly important as epitaxial layer structures become more complex and the thickness and alloy composition tolerances are reduced. The technique of spectroscopic ellipsometry has been adapted to a commercial III–V semiconductor molecular beam epitaxy (MBE) system to monitor layer thickness, ternary alloy composition, and substrate temperature in real time during the growth of multilayer structures. Practical system considerations for reliably implementing the rotating analyzer ellipsometer in a hydride source MBE environment that contains a high pressure of dimeric group V species will be discussed. Measurement of substrate temperature from room temperature to typical growth temperatures will then be presented as well as in situ determination of alloy composition and thickness for efficient growth calibration. A growth run of GaAs/AlGaAs epitaxial layers will be examined to observe surface smoothing upon group III pulse deposition and growth interruption at heterointerfaces. The growth of quantum well structures is then monitored and analyzed in attempts to extract heterojunction interface abruptness. Finally, a summary of epitaxial reactor design issues that need to be addressed to implement the spectroscopic ellipsometry (SE) technique in commercial systems is provided.