Optical properties of Hg1−xMnxTe1−ySey

doi:10.1016/j.infrared.2004.06.007

Infrared Physics & Technology

Volume 46, Issue 5, June 2005, Pages 379-387

https://doi.org/10.1016/j.infrared.2004.06.007 Get rights and content

Abstract

Far-infrared reflectivity spectra of Hg_1−xMn_xTe_1−ySe_y (0.01 ⩽ x ⩽ 0.14, 0.01 ⩽ y ⩽ 0.1) single crystals were measured in the 80–420 cm⁻¹ range at room temperature. The analysis of the far-infrared spectra was made by a fitting procedure based on the model of coupled oscillators. The dependence of plasma frequency and phonon modes on composition was determined. A model for phonon behavior in quaternary mixed crystals of the type A_1−xB_xC_1−yD_y was developed, too. This model was tested for Hg_1−xMn_xTe_1−ySe_y.

Introduction

Hg_1−xMn_xTe_1−ySe_y is a semimagnetic semiconductor made from two three-component diluted magnetic narrow-gap semiconductors—Hg_1−xMn_xTe and Hg_1−xMn_xSe, which have been studied before [1], [2]. It has been found that Hg_1−xMn_xTe has a p-type conductivity [3], while Hg_1−xMn_xSe always has an n-type conductivity with a high electron density [4]. The type of conductivity is connected with charge defects appearing in the crystals: Vacancies in the mercury sublattice are acceptors in Hg_1−xMn_xTe, while mercury atoms at interstitials and vacancies in the selenium sublattice are donors in Hg_1−xMn_xSe. It may be assumed that varying the selenium concentration will produce a particular kind of compensation of the various defects.

Hg_1−xMn_xTe_1−ySe_y solid solutions have revealed interesting electronic and magnetic properties different from those of the constituent systems [5], [6], [7]. Even though the band structure is essentially the same as those of the hosts, the Mn-induced acceptor impurity band is enhanced in energy, the electron concentration is increased and the hole concentration in the impurity band remains almost unchanged, but second type holes appear additionally in the solid solutions [7]. These three types of conduction carriers are found to be responsible for the temperature and magnetic field dependences of the observed Hall coefficients, in contrast to the two-carrier model valid for the host Hg_1−xMn_xTe [3] or a single-carrier model for Hg_1−xMn_xSe [4].

Far-infrared reflection spectra were previously measured [8] but only for one concentration of Se (y = 0.01). No qualitative analysis was done and as a consequence of that and of the high concentration of free carriers (plasmons), the phonons registered were wrongly assigned. Also, the measured phonons were not discussed in the frame of any model. We examined eight samples with different compositions (0.01 ⩽ x ⩽ 0.14, 0.01 ⩽ y ⩽ 0.1). For reflectivity spectra analysis we applied a model that includes plasmon–phonon interaction [9] and determined phonon frequencies precisely. To analyze the phonons we used the models [10], [11], [12], which, with various modifications, were used to analyze phonons in three component mixed crystals. We introduced the necessary modifications to apply this model to four-component mixed crystals.

In this work the far-infrared reflection spectra were measured at room temperature. The analysis of these spectra is done and the plasma frequency (ω_p) and optical modes (TO and LO) are determined.

Section snippets

Samples and experiment

Single crystals of Hg_1−xMn_xTe_1−ySe_y were grown by the Bridgman technique from chemically pure components. The value of Mn concentration x was determined with an error of ±0.005 from the magnetic susceptibility at room temperature measured by a Faraday method at H = 1000 Oe, where the diamagnetic contribution of the host HgTe (χ_d = −(2.3 − 3.6) × 10⁻⁷ emu g⁻¹) [1] was neglected; even if χ_d is taken into account, the x value is increased by 0.01 at most. Also, the manganese content was determined (more

Results and discussion

The far-infrared reflection spectra of the Hg_1−xMn_xTe_1−ySe_y single crystal samples are shown in Fig. 1. The experimental data are represented by circles. The solid lines were obtained using a modified factored dielectric function model of coupled plasmon–LO phonon modes [9] (Eq. (1)).

From Fig. 1 we can see that these spectra are very different for various compositions. For some spectra the plasma minimum is on the low wave numbers and then phonon modes are clearly observable. For some other

Optical phonons

There has been great interest in studying the long-wavelength optical phonons in mixed crystals by means of infrared spectroscopy and Raman scattering. This interest is due to the importance of certain mixed semiconductors for solid state devices. Most of the mixed crystals studied were of the AB_1−xC_x type. One of the most successful models which has been used to treat the optical behavior of a mixed crystal AB_1−xC_x is the random element isodisplacement model (REI model) of Chen et al. [10] and

Conclusion

In this paper we used far-infrared reflectivity measurements to obtain phonon properties of Hg_1−xMn_xTe_1−ySe_y mixed crystals. Concentration dependence of plasma frequency at room temperature was determined, and connected with the existence of three types of carriers in this material.

We also developed the model that describes the optical modes of quaternary mixed crystals of the type A_1−xB_xC_1−yD_y. On the basis of this model one can determine optical mode frequencies of some A_1−xB_xC_1−yD_y compound,

Acknowledgement

This work is supported by Serbian Ministry of Science, Technology and Development under project 1481.

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Optical properties of Hg1−xMnxTe1−ySey

Abstract

Introduction

Section snippets

Samples and experiment

Results and discussion

Optical phonons

Conclusion

Acknowledgement

Solid State Commun.

Solid State Commun.

Solid State Commun.

Infrared Phys. Tech.

Solid State Commun.

J. Appl. Phys.

Adv. Phys.

Zh. Eksp. Teor. Fiz.

Fiz. Tekh. Poluprovodn.

Semicond. Sci. Technol.

Zh. Eksp. Teor. Fiz.

Semiconductors

Semiconductors

Optical properties of Hg_1−xMn_xTe_1−ySe_y