Optical properties of wide-band-gap chalcopyrite CuAl(Se0.5S0.5)(2) evaluated by thermoreflectance spectroscopy

作者：Ho Ching Hwa^*; Pan Chia Chi

来源：Optical Materials Express, 2013, 3(4): 480-488.

DOI：10.1364/OME.3.000480

The band edge and higher-lying interband transitions of CuAl(Se0.5S0.5)(2) compound have been characterized using thermoreflectance (TR) measurements at room temperature. Single crystals of CuAl(Se0.5S0.5)(2) were grown by chemical vapor transport method using ICl3 as the transport agent. The TR measurement results showed three interband transitions denoted as E1, E2, and E3 detected near the band edge of CuAl(Se0.5S0.5)(2) chalcopyrite compound. The lowest-energy transition is the main band-edge transition positioned at E1 = 2.96 eV, the second is E2 = 3.05 eV, and the other higher-energy transition is E3 = 3.202 eV, respectively. Polarized-thermoreflectance (PTR) measurements showed that the E1 and E2 transition features are observed only with the linearly polarized light along the epsilon parallel to%26lt;11%26lt;(1)over bar%26gt;%26gt; (needle axis) direction while the E3 transition largely appears with the electrical field of e perpendicular (perpendicular to) to the needle axis. The E1 and E2 transitions may originate from the valence-band top while the E3 transition is closely related to the valence-band splitting in the crystal. To characterize the anisotropic properties of electronic structure of CuAl(Se0.5S0.5)(2), PTR measurements were carried out over a wide energy range of 2.5-6 eV. The interband transitions belonging to E-parallel to or E-perpendicular to polarization are respectively identified. On the basis of experimental analysis, the electronic structure near the fundamental band edge of CuAl(Se0.5S0.5)(2) has thus been determined.

• 出版日期2013-4-1