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

Abstract

In this work in-situ spectroscopic ellipsometry (SE) has been applied for the simultaneous determination of the growth temperature and alloy composition for the epitaxial Cd 1-x Zn x Te(211)/Si(211) structure. The optical dielectric functions of CdTe and Cd 0.96 Zn 0.04 Te (CZT) epilayers were studied as a function of temperature both ex-situ and in-situ in the range from 1.6 eV to 4.5 eV. We employed parametric models for the simulation of the optical properties of CZT at and between the critical points (CP) E 0 , E 0 + ∆ 0 , E 1 , E 1 + ∆ 1 , E 2 (∑) and E 2 (Σ). Critical point energies and line widths for Cd 1-x Zn x Te 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. It has been demonstrated that the energy of the weak E 0 + ∆ 0 transition can be used to measure composition, while the E 1 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. Our 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.

Polarization Dependent Reflectivity and Transmission for Cd1-Xznxte/GaAs(001) Epifilms in the Far-Infrared and Near-Infrared to Ultraviolet Region

“…In calculating the optical constants for the Cd 1-x Zn x Te ternary alloys with x=0.0, 0.11, 0.64, 0.86 and 1.0 (Figures 5a and 5b), we have evaluated the CP energy parameters from the values of its binary counterparts and used the quadratic expressions involving x, while the energy strength and broadening parameters are obtained deliberating linear dependence articulations on x. Once again, the results (Figures 5a and 5b) of the optical parameters for ternary Cd 1-x Zn x Te alloys are found not only consistent with the limited SE data [16][17][18][19] but has also provided clear revelations of the composition dependent CP energy shifts and widths. in the transparent photon energy region -except that they disclosed the broad intensity modulations.…”

“…While the composition-dependent EXAFS data revealed a bimodal distribution of nearest-neighbor bond lengthstheoretical analysis by first-principles bond-orbital model permitted an accurate appraisal of the lattice relaxations around Zn/Cd atoms in CdTe/ZnTe materials. One must note that only limited efforts have been made by SE to uncover the optical properties of CZT alloys in the near-IR (NIR) to ultraviolet (UV) energy range [16][17][18][19][20]. From a theoretical stand point, it has now become possible [14,15] to expend pragmatic model dielectric functions (MDFs) of binary materials to elucidate structural and optical characteristics of semiconducting ternary alloys, and SLs grown on different substrates.…”

Measuring of composition of Cd<inf>1&#x2212;X</inf>Zn<inf>x</inf>Te layer by spectral ellipsometry method

“…The composition can be controlled based on spectral location of these points. Their dependences on compositions can be found in [4,5] and other papers , however there are differences caused by different measuring techniques.…”

“…For the measurement of the composition of thin surface layer it is possible to use peak of low intensity of E o +,1 o , which sensitivity to the composition according to [4] is somewhat higher than that of Eo. Penetration depth of light in the area of spectrum close to E o +,1 o is about 500nm therefore the measurements of location of this critical point can provide supplementary information for thick films.…”

MBE growth of HgCdTe HOT detector heterostructures

“…By employing sophisticated parametric dispersion models and simultaneously fitting the spectroscopic ellipsometric spectra, we can get the information on the HgCdTe layer (composition and surface roughness, etc.) over the growth time [3]. Shown in figure 2 are the experimental ellipsometric spectra obtained from the CdZnTe substrate and during HgCdTe growth.…”