J. Cebulski

Far-infrared reflectivity as a probe of point defects in Zn- and Cd-doped HgTe

We present a nondestructive method for quantitative determination of the vacancy concentration in the lattice of Hg-based semiconductor alloys with tetrahedral structure. The method is based on the identification of additional vibrational modes (AVMs) induced by lattice deformations in the far-infrared (FIR) reflectivity spectrum. Although the method is restricted by sensitivity limitations, recent FIR experimental data carried out on HgZnTe and HgCdTe samples containing Hg vacancies confirmed the presence of AVMs induced by Hg vacancies in as-grown crystals.

Phonon and vibrational spectra of hydrogenated CdTe

This work presents far-infrared reflectivity spectra collected with synchrotron radiation on specially prepared CdTe monocrystals in the temperature region of 30–300K. The investigated samples were of three different types characterized by the three different levels of hydrogenation—strong, middle, and low ones. In order to interpret the experimental data, the imaginary part of the dielectric function was evaluated by means of Kramers-Kronig transformation. To determine quantitatively the influence of hydrogen atoms on the phonon and vibrational spectra of hydrogenated CdTe crystals we used the special statistical model proposed in this paper. This model takes into account the tetrahedron as the basic structural unit and distinguishes the contribution of the hydrogen-bearing tetrahedra from the contribution of the hydrogen-free ones to the crystal phonon spectra.

Statistical model analysis of local structure of quaternary sphalerite crystals

At the 2004 Ural International Winter School, we introduced the statistical strained tetrahedron model and discussed ternary tetrahedron structured crystals. The model allows one to interpret x-ray absorption fine structure (EXAFS) data and extract quantitative information on ion site occupation preferences and on the size and shape of each elemental constituent of the configuration tetrahedra. Here we extend the model to cover quaternary sphalerite crystal structures. We discuss the two topologically different quaternary sphalerite systems: the pseudo-balanced A1−xBxYyZ1−y (2:2 cation:anion ratio), and the unbalanced AxBx′C1−x−x′Z or AXyYy′Z1−y−y′ (3:1 or 1:3 cation:anion ratios) truly quaternary alloy systems. These structural differences cause preference values to vary with the relative contents in pseudo-quaternaries but to remain constant in truly quaternary compounds. We give equations to determine preference coefficient values from EXAFS or phonon spectra and to extract nearest-neighbor inter-ion d...

Magnetophonon resonance as method of controlling of the thermal stress in the multiple quantum wells

The magnetophonon resonance (MPR) is very sensitive to the smallest changes of the material parameters and could be applied to the study of thermal stresses in multiple quantum wells (MQWs). Stresses in MQW layers caused by mismatch between the QW lattice and the barrier should be accounted for when the measurement temperature is lower than the temperature of creation of the layers with MOCVD technology. Mismatch leads to a tension in the plane of the QW layers. Because of their various distributions in the MQW their contribution, sign included, to the shift of the resonance field will vary. It is this effect that can explain the disintegration of magnetoconductivity in MQW during parallel transport. MPR in parallel transport of two types MQWs were studied. A fine structure of MPR peaks which depends on temperature and does not depend on the type of MQW, was observed. This effect is attributed to two phenomena: contribution of barrier phonons and influence of thermostresses.

Influence of the electron-phonon interaction on the temperature dependence of the phonon mode frequency in the II-VI compound solid solutions

We present an experimental investigation of the temperature dependence of the TO-phonon mode frequencies for the HgTe-based II-VI semiconductor solid solutions. In the case of the ternary Hg0.9Zn0.1Te solid solution was shown a discontinuity in the temperature dependence of the HgTe-like T0-mode and of the ZnTe-like T1-mode, similar to the Hg0.85Cd0.15Te system [Sheregii et al., Phys. Rev. Lett. 102, 045504 (2009)]. A generalization of the theoretical temperature shift of the phonon mode frequency as analytic equation is derived that includes both the anharmonic contribution and the electron-phonon e-p interaction which in this case is returnable—the electron subsystem effect on the phonon one. Data show that our equation satisfactorily describes the temperature shift of both Hg0.85Cd0.15Te and Hg0.90Zn0.10Te containing Dirac point (Eg ≡ Γ6 – Γ8 = 0) although one of the two constants describing the anharmonic shift of the HgTe-like mode should be positive what is abnormal too. In the case of the Hg0.80Cd0...

MAGNETOPHONON RESONANCE IN MnxCdyHg1-x-yTe

The aim of this work is to analyze the band-structure parameters of MnxCdyHg1-x-yTe (MMCT) alloys by means of Magnetophonon Resonance (MPR) and to compare that obtained for ZnxCdyHg1-x-yTe (ZMCT). MPR was observed for two samples of MnxCdyHg1-x-yTe (MMCT) (I- x=0.095 and y=0.09, II-0.04 and y=0.19). The measurements of MPR were performed in pulsed magnetic fields at different temperatures ranging from 77 K to 200 K. The several wide maxima are clearly visible on the experimental curves corresponding to four series of peaks. These series are related to three kinds of phonons analogous to ZMCT. The system of MPR peaks in MMCT is shifted significantly to the higher magnetic fields in comparison with the ZMCT resonance curves of approximately the same content of Zn. The value of effective mass obtained by MPR experiment is of 66% greater than those calculated in the framework of three-band Kane model, in which the value of Eg, was extracted from the photoconductivity data.