TEMPERATURE AND COMPOSITION DEPENDENCE OF EXCITON PEAK POSITIONS AND BAND-GAP ENERGIES OF ZN1-XMGX(LESS-THAN-OR-EQUAL-TO-0.19)SE EPITAXIAL-FILMS

The temperature dependence of the Is exciton energy has been measured in Zn1-xMgxSe epitaxial films sat compositions x=0, 0.07, 0.12, and 0. 19 from 2 K up to 280 K. Detailed numerical fits of the individual tem perature dependences are provided on the basis of an analytical four-p arameter representation developed recently by one of the authors. Thes e are compared with previously used three-parameter models of Villa et al. and Varshni. The cc-dependence of the exciton energy, E-1s(T, x), and of the fundamental band gap energy, E-g(T, x), is given to very g ood approximation by linear functions of the composition x for any T f rom absolute zero up to room temperature. A comparison with recent roo m temperature band gap energy data by Jobst et al. shows that this lin ear dependence holds up to x approximate to 0.7. The magnitudes of the model-dependent empirical parameters, which control the temperature d ependence of the band gap energy in different compounds, are found to change significantly with increasing magnesium content. From the magni tude of the effective phonon temperature, particularly in the case of ZnSe, we conclude that the main contributions to the band gap shrinkag e effect are due to acoustic phonons.