Mechanisms of current flow in p-TlGaSe₂single crystals

Abstract

Temperature dependences of dark current, i(T ), thermally stimulated current, TSC, and current-voltage, I-V, characteristics have been investigated in p-type TlGaSe 2 single crystals having different technological origins, using different contacts, in a wide temperature range and at different heating rates. Two types of initially undoped crystals with high resistivity, differing in deviation from the stoichiometry (type 1 and type 2), have been investigated. It is shown that the mechanism of the current flow strongly depends on the technological origin of the sample. Negative TSC is observed in type 1 samples for the first time and attributed to the simultaneous release of holes and electrons from acceptor and donor states in the same temperature interval. In these types of crystals, the dark current appears due to the double injection of electrons and holes from the contacts and at high heating rates β 8-10 K min -1 has a thermally activated character. The parameters of subsequent impurities have been obtained using the TSC theory. The shallow donor states with extremely low capture cross sections were shown to contribute to the thermally activated processes in these types of crystals. In type 2 crystals low-frequency current oscillations, LFCO, have been observed for the first time in the temperature range 120-180 K. These types of crystals are characterized by nonlinear N-type I-V characteristics. Mechanisms are proposed to explain the nonlinear I-V characteristics and current oscillations.

The Franz–Keldysh effect in the optical absorption spectrum of a TlGaSe2 layered semiconductor caused by charged native defects

“…Therefore, the electrons on the donor levels that are partially compensating a number of holes on the acceptor levels must also be present in the TlGaSe 2 . The existence of such native donor levels directly below the conduction band minimum has been experimentally confirmed by our previous work in the pristine TlGaSe 2 sample [31]. The energy levels of these donors are found to be quite shallow; so they cannot lead to appreciable scattering or trapping of the electrons [31].…”

“…The existence of such native donor levels directly below the conduction band minimum has been experimentally confirmed by our previous work in the pristine TlGaSe 2 sample [31]. The energy levels of these donors are found to be quite shallow; so they cannot lead to appreciable scattering or trapping of the electrons [31]. Presumably, Se antisite or interstitial defects could create the lower-energy shallow donor-like defects in the electronic bandgap of TlGaSe 2 .…”

“…It is well known that undoped TlGaSe 2 is a partially self-charged compensated semiconductor with high resistivity and has low carrier concentration at room temperature [31]. Therefore, the electrons on the donor levels that are partially compensating a number of holes on the acceptor levels must also be present in the TlGaSe 2 .…”

A Study of Thermoelectric Performance of TlGaSe2 Layered Dichalcogenides from First‐Principles Calculations: Vacancy Defects Modeling and Engineering

“…[ 1–4 ] In bulk form, is a p‐type semiconductor with optical bandgap in the visible spectral range (≈2.1 eV) at room temperature. [ 5–9 ] grows in the form of multilayers where layers are weakly interacting through van der Waals forces along the direction. Within the layers, every atom is strongly bonded with neighbor ones via ion‐covalent chemical bonding mechanism.…”

“…At room temperature the electronic transport mechanism in the direction parallel to the layers is directly related to the presence of localized states in the bandgap created by native structural defects. [ 7–19 ] The electrical conduction perpendicular to the layers is expected to be highly sensitive to inevitable structural defects such as: planar defects presented between the layers due to a slipping of successive layers, point defects, charged impurities, deep level traps, dislocations as well as to many other crystal lattice imperfections that are mainly attributed to the interlayer stacking faults. [ 20–22 ] Only at extremely high temperatures, due to the thermally activated free carriers from the valence band the intrinsic electrical conduction is determined by a band‐to‐band mechanism.…”