Apart from the possible applications of I-III-VI₂ chalcopyrite-type semiconductors in opto-electronics and nonlinear optics, there has been a significant interest in the investigation of their physical properties. Unlike their II-VI analogs, the anomalous behavior displayed by these semiconductors is of particular interest.  

In the present work, CuGaS₂ (CGS) and AgGaS₂ (AGS) crystals with different isotopic compositions were synthesized from their constituent elements in order to study their electronic, vibrational and thermodynamic properties. Before employing the chemical vapor transport (CVT) as growth method [1, 2], sulfur and copper were purified by sublimation and etching, respectively. The ¹⁰⁹Ag and the etched ⁷¹Ga isotopes were purified from oxides by vacuum annealing. Elemental iodine or AgI was then added as transport agent with a concentration of 2-4 mg/cm³ (CGS) and 0.5-1.2 mg/cm³ (AGS). The source temperature was set to 880-940°C, yielding yellow, orange and green colored crystals (in the temperature range of 800-880°C) in the shapes of platelets, chunks, rods and needles of up to 7 mm (CGS) and 30 mm (AGS) in sizes. The surfaces of these crystals were observed to be plane (faceted), rounded or rough. At the source, crystals grew in dark and even in black color. The deposition of binary sulfides and iodides on the crystal surfaces during the ampoule cooling was prevented by a cold trap in order to preserve the surface quality. The ternary compound compositions of the grown crystals were confirmed with Raman-spectroscopy.

The higher excitonic states (n = 2, 3) observed in these crystals at low temperatures with wavelength-modulated reflectivity indicate an excellent surface and crystalline quality. In addition, the experimentally determined non-monotonic temperature dependence of excitonic energies produces a good agreement with the Bose-Einstein oscillator model [3, 4]. Isotopic shift of excitonic energies has also been successfully observed in these crystals [5] and experimental results of heat capacities show a good agreement with the ab initio calculations [6, 7].

References:

[1] Y. Noda et al., J. Cryst. Growth 99 (1990) 757

[2] R. Lauck, J. Cryst. Growth 312 (2010) 3642

[3] J. Bhosale et al., Phys. Rev. B 86 (2012) 195208

[4] J. Bhosale et al., APS March Meeting 2013

[5] J. Bhosale et al., APS March Meeting 2012

[6] A.H. Romero et al., Phys. Rev. B 83 (2011) 195208

[7] M. Cardona et al., AIP Conf. Proc. 1506 (2012) 40

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29633 must be provided.

1. C.V. Raman and the Impact of Raman Effect in Quantum Physics, Condensed Matter, and Materials Science
2. The widths of phonons
3. The widths of phonons
4. Lattice Dynamics of Wurtzite ZnO: an Experimental and Ab-initio Study