On the Optical Properties of Defect-Chalcopyrite Single Crystals: The Aluminium Compounds HgAl 2 Se 4 , CdAl 2 Se 4 and ZnAl 2 Se 4

• Published in: Japanese Journal of Applied Physics 2000-01, Vol.39 (S1), p.98
• Main Authors: Eifler, Andreas, Riede, Volker, Hecht, Jan-David, Krauss, Günter, Krämer, Volker, Grill, Wolfgang
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.7567/JJAPS.39S1.98

Using both infrared and Raman spectroscopy all of the optical phonon modes of the materials under investigation have been observed and assigned to the irreducible representation of the point group of the crystals. The infrared reflectivity spectra of HgAl 2 Se 4 as well as of oriented CdAl 2 Se 4 single crystals show five well separated optical phonon modes for both directions of polarization, behaviour which is predicted by group theory for A II B III 2 C VI 4 compounds crystallizing in space group I 4̄. ZnAl 2 Se 4 has been found to crystallize in space group I 4̄2m with a statistical distribution of the vacancies and half the aluminium atoms at the sites 4d. In the infrared reflectivity spectra of various ZnAl 2 Se 4 samples in comparison with HgAl 2 Se 4 and CdAl 2 Se 4 , the low frequency mode of B symmetry is missing. The optical properties in the band gap region have been determined using polarized transmittance and reflectivity measurements and diffuse reflectivity measurements. The estimated band gap energies at room temperature are 2.20 eV, 3.05 eV and 3.30 eV for HgAl 2 Se 4 , CdAl 2 Se 4 and ZnAl 2 Se 4 , respectively.