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

• Published in: Journal of electronic materials 2000-06, Vol.29 (6), p.742-747
• Main Authors: Daraselia, M., Brill, G., Garland, J. W., Nathan, V., Sivananthan, S.
• Format: Article
• Language: English
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-000-0218-x

In-situ spectroscopic ellipsometry (SE) has been applied for the simultaneous determination of the growth temperature and alloy composition for the epitaxial Cd1-xZnxTe(211)/Si(211) structure. The optical dielectric functions of CdTe and Cd0.96Zn0.04Te(CZT) epilayers were studied as a function of temperature both ex- and in-situ in the range from 1.6 to 4.5 eV. Authors employed parametric models for the simulation of the optical properties of CZT at and between the critical points (CP) E0, E0 + DELTA0, E1, E1 + DELTA 1, E2(SIGMA) and E2(SIGMA). Critical point energies and line widths for Cd1-xZnxTe were obtained through the fitting process, which 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. The energy of the weak E0 + DELTA0 transition can be used to measure composition, while the E1 energy can be used as a real-time temperature measure. The model parameters were optimized through the simultaneous analysis of multiple data sets, and the temperature dependent model was developed for in-situ application. Analysis is estimated to produce uncertainties of only +-0.5 C in measuring the temperature and +-0.5% in measuring the composition if only the zero order dielectric function is being fitted. The effects of a surface overlayer, of reflected beam deflections, and of other experimental problems on the overall accuracy, are discussed as well as ways to improve the in-situ SE data quality. 16 refs.