Phase modulated ellipsometry used for composition control during MBE growth of CdHgTe: An analysis of instrumental factors and an assessment of the material produced

Abstract

We have found phase modulated ellipsometry (PME) to be a sensitive analytical technique capable of providing real time information on composition, epilayer thickness, growth rate, interdiffusion and surface roughness. To fully exploit the benefits of PME, the instrument must be carefully calibrated and the many factors affecting its performance need to be understood and allowed for. In this paper we examine how the accuracy of the determination of composition of molecular beam epitaxially grown CdHgTe alloy films is affected by misalignment of the optical components, the presence of vacuum windows, signal conditioning prior to analog to digital conversion, temperature changes, and modulator settings. We conclude by presenting results which demonstrate the quality of CdHgTe layers grown on (211)B CdZnTe and (211)B GaAs substrates using our techniques.