Band gap and refractive index tunability in thallium based layered mixed crystals

Abstract

Compositional variation of the band gap energy and refractive index of TlMeX 2-type (Me ¼ Ga or In and X ¼ S or Se) layered mixed crystals have been studied by the transmission and reflection measurements in the wavelength range of 400-1100 nm. The analysis of absorption data of TlGa 1-x In x Se 2 , TlGa(S 1Àx Se x) 2 , TlGa 1Àx In x S 2 , and TlIn(Se 1Àx S x) 2 mixed crystals revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps of mixed crystals decrease at the replacing of gallium atoms by indium and of sulfur atoms by selenium ones. Through the similar replacing of atoms (smaller atoms by larger ones) in the studied mixed crystals, the refractive index shows the quite opposite behavior. V

Band edge photoluminescence of undoped and doped TlInS 2 layered crystals

“…1 demonstrates a sharp absorption increase for quanta energy above 2.27 eV. This value coincides with a customary indirect band gap E i G at k||c obtained by a simple linear extrapolation of the absorption coefficient in the (αhν) 1/2 -hν coordinates [15]. The position of the direct band gap…”

“…The incorporation of Ag, B, Er was carried out by addition to the melt with molar concentrations of atoms in the range of 0.1-0.5%. As noted previously [7,12,14,15], the incorporation of doping to this level maintain the atomic ratio of constituent elements. The crystals were cut onto parallelepiped pieces normal to the sample plain with a lateral size of a few millimeters and thickness up to hundred micrometers.…”

“…(The typical map of the results via this method is exposed in Refs. [10,15,18].) We have found that the presence of B and Ag doping atoms in TlInS 2 give reduction of the transmission below E i G .…”

Carrier dynamics in highly excited TlInS2: evidence of 2D electron–hole charge separation at parallel layers

“…The energies for lowest direct exciton and indirect band gap at RT are E x d = 2.44 eV and E g i = 2.26 eV, respectively. [24,25] Besides, the direct exciton absorption is relatively low, and absorption is restricted to the values of about 10 3 cm -1 . [3,26] In our previous work, it was discovered that polarization of the emitting light from TlGaSe 2 is outof-layer plane, suggesting the e-h emitting dipoles (excitons) are orthogonal to the crystal layer.…”