In-situ control of temperature and alloy composition of Cd1-xZnxTe grown by molecular beam epitaxy

In this work in-situ spectroscopic ellipsometry (SE) has been applied for t he simultaneous determination of the growth temperature and alloy compositi on for the epitaxial Cd1-xZnxTe(211)/Si(211) structure. The optical dielect ric functions of CdTe and Cd0.96Zn0.04Te (CZT) epilayers were studied as a function of temperature both ex-situ and in-situ in the range from 1.6 eV t o 4.5 eV. We employed parametric models for the simulation of the optical p roperties of CZT at and between the critical points (CP) E-0, E-0 + Delta(0 ), E-1, E-1 + Delta(1), E-2(Sigma) and E-2(Sigma). Critical point energies and line widths for Cd1-xZnxTe were obtained through the fitting process, w hich included both zero order and higher order derivatives of the SE pseudo dielectric function. The dependence of the different critical points on Zn concentration x is discussed. It has been demonstrated that the energy of the weak E-0 + Delta(0) transition can be used to measure composition, whil e the E-1 energy can be used as a real-time temperature measure. The model parameters were optimized through the simultaneous analysis of multiple dat a sets, and the temperature dependent model was developed for in-situ appli cation. Our analysis is estimated to produce uncertainties of only +/- 0.5 degrees C in measuring the temperature and +/- 0.5% in measuring the compos ition if only the zero order dielectric function is being fitted. The effec ts of a surface overlayer, of reflected beam deflections, and of other expe rimental problems on the overall accuracy, are discussed as well as ways to improve the in-situ SE data quality.