The results from the investigation of optical absorption in TlGaSe 2 layered bulk semiconductor in the wavelength range of 400-900 nm between the temperatures of 19 K and 300 K are presented and discussed. In the results, the layered semiconductor TlGaSe 2 is interpreted as a direct band gap semiconductor with a band gap of about 2.04-2.14 eV at 300 K. Additionally, the optical transmission spectrum of TlGaSe 2 exhibited some peculiarities, which were attributed to indirect allowed interband transitions. It has been explained that the optical absorption edge of TlGaSe 2 can be characterized by the presence of an Urbach-like tail as well as a high-energy Tauc absorption region. The Tauc slope and Tauc energy gap were extracted from the absorption coefficient data by using the Tauc procedure. The results revealed that the 'amorphized' structure of TlGaSe 2 which is prominent in near conduction/valance band energy states, cannot be ignored for the understanding of the optical transition mechanisms in this semiconductor.

We report on the characteristics of metal-p-type high resistance TlGaSe2 semiconductor junction barrier fabricated by deposition of indium and gold metals. The electrical properties of /TlGaSe2/ semiconductor contacts were monitored as a function of temperature in the range of ∼80–300 K using current–voltage ( I − V ) and capacitance–voltage ( C − V ) measurements. Device characteristics of I n /TlGaSe2/ A u showed rectification properties. From forward bias I − V characteristics it was revealed that the increase of current is slower than the predictions by Schottky barrier theory. The rectification properties of I n /TlGaSe2/ A u semiconductor device were simulated by the Mott barrier model where the presence of an undoped layer on the semiconductor surface is assumed, and measurements and computational simulation agreed on the validity of this model. C − V measurements showed that at higher temperatures I n /TlGaSe2/ A u barrier showed a capacitance from accumulation toward depletion mode, whereas at low temperatures the barrier capacitance degradation was found. The observed C − V of I n /TlGaSe2/ A u does not significantly change over the entire bias range ± 30 V, confirming that the I n /TlGaSe2/ A u is fully depleted, thus the structures are Mott barrier. First-principles electronic band diagram calculations showed that introduction of S e -atom vacancies in the various sites of TlGaSe2 unit cell greatly affects the electronic band structure of this semiconductor in an increasing manner in band gaps with respect to stoichiometric compound. Consequently, the S e - vacancies localized inside the thin surface layer of TlGaSe2 are responsible for high average surface electrical resistivity of the material and could be proposed as a physical basis for the existence of native insulator layer on TlGaSe2 surface. Thus we propose a model for TlGaSe2 crystal which is comprised from an electrically conducting bulk semiconductor sandwiched between two high resistivity thin surface sheets. We suggest that the selenium vacancy defects on the surface of TlGaSe2 layered semiconductor are also responsible for the memristive behavior of this compound.

Herein, the thermoelectric performance of TlGaSe2 ternary layered dichalcogenides is evaluated by applying ab initio density functional theory calculations combined with Boltzmann's transport equation. A novel approach to design the intrinsic structural defects via Se‐anion vacancies in unit cell has been developed. Two kinds of Se‐vacancy defects in host TlGaSe2 crystal lattice are engineered: the single vacancy defect induced intrinsically in the unit cell (1×1×1) and in the supercell lattice (1×1×4). It is found that the electrical transport properties and thermoelectric efficiency of this semiconductor could be significantly altered by introducing Se‐vacancy states into crystalline structure. In addition, simulation shows that inclusion of Se‐vacancy defects significantly improves the thermoelectric efficiency as well as the thermoelectric power factor and figure of merit (ZT) values of this compound. Additionally, the thermoelectric performance of TlGaSe2 is estimated by means of the electronic fitness function calculations in the valence and conduction edges. The results demonstrate that TlGaSe2 with introduced Se‐vacancies may be a perspective material for thermoelectric applications.