Determination and modeling of the optical constants of direct band gap Be _x Zn _{1− x} Te grown by molecular beam epitaxy

Abstract

PACS 78.20.CiThe optical constants ε(E) of direct band gap Be x Zn 1-x Te have been measured at 300 K using spectral ellipsometry (0.73-6.45 eV). The ε(E) spectra displayed distinct structures associated with critical points at E 0 , E 0 +∆ 0 , E 1 , E 1 +∆ 1 , e 1 +∆ 1 and E 2 . The experimental data over the entire measured spectral range has been fit using the Holden-Muñoz model dielectric function, which is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E 0 , E 0 +∆ 0 and the E 1 , E 1 +∆ 1 , doublet. In addition to evaluate the energies of these various band-to-band critical points, information about the binding energy (R 1 ) of the two-dimensional exciton related to the E 1 , E 1 +∆ 1 critical points was obtained. The value of R 1 was in good agreement with effective mass theory. The ability to evaluate R 1 has important ramifications for first-principles band-structure calculations that include exciton effects at E 0 , E 1 , and E 2 . 1 Introduction II-VI semiconductor optoelectronic devices based on beryllium are currently under investigation in order to overcome important problems such as low p-type doping carrier concentration and degradation issues present in several II-VI devices. In order to design efficient optoelectronic devices involving these compounds a detailed study of the optical constants of Be x Zn 1-x Te as well as its relation with their band structure is necessary. However, in spite of its fundamental and applied significance, relatively little work has been reported on the optical properties related to the electronic band. Some authors [1] performed measurements of the ZnTe dielectric function but modeled the optical constants not including continuum exciton contributions, i.e., band-to-band Coulomb enhancement (BBCE) effects at E 0 , E 0 +∆ 0 , E 1 , E 1 +∆ 1 critical points (CPs). References [2] and [3] using Fourier analysis and a second derivative analysis of the dielectric function, respectively, were able to obtain the energies of features related to the CPs. Reference [3], using a second derivative analysis of the dielectric, function provided the only study available of the energies of features related to the CPs of Be x Zn 1-x Te for x > 0. In this work we present a study of the optical constants of direct band gap Be x Zn 1-x Te and their relationship with their band structure. The ε(E) spectra of the different samples displayed distinct structures associated with CPs at E 0 , E 0 +∆ 0 E 1 , E 1 +∆ 1 , the e 1 +∆ 1 feature, as well as E 2 . The experimental data over the entire measured spectral range has been fit using the Holden-Muñoz model [4] dielectric function, which is based on the electronic energy-band structure near the CPs plus excitonic and BBCE effects. In addition to evaluating the energies of these various band-to-band CPs, information about the binding energy (R 1 ) of the two-dimensional exciton related to the E 1 and E 1 +∆ 1 CPs was obtained. The value of R 1 was

Optical Properties

“…The x dependence of E 0 has been determined from this study. SE has also been used to measure « 2 (E) in Be x Zn 1Àx Te [233][234][235].…”