In nominally undoped layered TlGaSe2 crystals the trapping centers have been investigated by photo‐induced current transient spectroscopy (PICTS). Five acceptor and donor traps have been detected. Quite large magnitudes of capture cross‐sections for donor traps at 0.23 and 0.45 eV have been determined. The depth‐resolved free‐carrier absorption (FCA) technique has been applied for the investigation of the majority hole lifetime, τR, at 295 and 77 K. The pronounced τR reduction with increasing injection level is attributed to the trapping effect of the minority electrons which provides a way of estimating trap centers concentration. A moderate τR variation across layer planes is observed but no carrier diffusion related to the recombination on the external crystal surfaces is detected. Moreover, abnormally sharp τR drop is found for carrier concentration above 1017 cm−3. The possibility of excess hole and electron special separation due to compositional stacking faults and the successive their enhanced recombination at high excess carrier concentrations is discussed.

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We reveal the intrinsic band‐to‐band photoluminescence (PL) in Tl‐based anisotropic semiconductors by means of confocal spectroscopy. The PL achieves largest value for k ⊥ c, where c is the layers stacking axis, and is dependent on polarization. In TlGaSe2, the band edge absorption spectra were determined at different excitation geometry by using techniques of depth‐resolved free‐carrier absorption (FCA) and photoacoustic response (PAR). A strong absorption enhancement is detected in a large spectral area in the near‐surface region lateral to ab plane. The band‐to‐band absorption enhancement is the most probable cause for high PL intensity. The near‐surface behavior, different from the bulk, might implement useful photonic functionality at room temperature (RT). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The depth-resolved free-carrier absorption and the photo-acoustic response are used to examine the band-gap absorption in 2D-TlGaSe2 layered semiconductor after its transformation into the ferroelectric F-phase below 107 K. The absorption exhibits unusual behavior with a biaxial character in respect to the light polarization on the layer plane. A spectral analysis shows that the anisotropy is associated to the lowest Γ-direct optical transition. The Γ-absorption and the localized exciton at 2.11 eV are dipole-prohibited or partially allowed in two nearly perpendicular polarization directions. The shift of anisotropy axis in respect to crystallographic a- and b-directions demonstrates the non-equivalent zigzag rearrangement of the interlayer connecting Tl+ ions, which is responsible for occurrence of the F-phase.

Intrinsic photoluminescence (PL) of undoped and of B-, Ag-or Er-doped TlInS 2 layered single crystals was investigated by confocal spectroscopy. It is found that position and intensity of PL spectral peak at 2.4 eV is vastly dependent on the excitation light incidence and polarization relative to crystallographic directions. For the normal incidence to the layer plane k||c, a significant Stokes shift between the PL peak in respect to exciton absorption energy is highlighted. The shift increases to 80 meV around the crystal phase transformations region of 200 K. We show that presence of B and Ag impurity do not diminish the intrinsic PL emission while Er atoms incorporation enhances it substantially and modifies a fine excitonic line structure in the ferroelectric phase at low T. The obtained results imply out-of-layer plain oriented 2D excitons in TlInS 2 existing at various crystal phases which are influenced by related interlayer stresses.& 2017 Elsevier B.V. All rights reserved. the TlInS 2 exhibit formation a new shallow donor-acceptor pair (DAP) photoluminescence band after low temperature thermocycling [6]. In addition, an imprint of photoactive trap self-polarization in the external electric field under different temperatures was observed and attributed to the dipolar origin of some Contents lists available at ScienceDirect