DEVELOPMENT OF A PARAMETRIC OPTICAL-CONSTANT MODEL FOR HG1-XCDXTE FORCONTROL OF COMPOSITION BY SPECTROSCOPIC ELLIPSOMETRY DURING MBE GROWTH

The development of an optical constant library for Hg1-xCdxTe as a fun ction of composition (x = 0-0.5) and temperature (T=0-250 degrees C) w hich is suitable for precise composition control by spectroscopic elli psometry (SE) during MBE growth is described. An efficient methodology for acquiring in situ optical constants as a function of composition and temperature is first presented. Optical constants extracted from t hese in situ measurements, as well as literature data from room temper ature values, were used to obtain internally Kramers-Kronig consistent parametric optical constant models at discrete compositions and tempe ratures. Then a global data analysis over temperature 'T' and composit ion 'x' was performed in which the internal parameters of the optical constant model were fitted as polynomials in T and x. This parametric model was developed to replace, without compromising the quality of el lipsometric data fits, the usual tabulated optical constant lists whil e using a reasonably small set of adjustable parameters. The model is flexible enough to describe the complicated critical point structures of semiconductors, yet stable enough to generate optical constants as a function of composition and temperature and permit limited extrapola tion outside the measured range. (C) 1998 Elsevier Science S.A.