Photoluminescence dynamics in few-layer InSe

Abstract

We study the optical properties of thin flakes of InSe encapsulated in hBN. More specifically, we investigate the photoluminescence (PL) emission and its dependence on sample thickness and temperature. Through the analysis of the PL lineshape, we discuss the relative weights of the exciton and electron-hole contributions. Thereafter we investigate the PL dynamics. Two contributions are distinguishable at low temperature: direct bandgap electron-hole and defect-assisted recombination. The two recombination processes have lifetime of τ1 ∼ 8 ns and τ2 ∼ 100 ns, respectively. The relative weights of the direct bandgap and defect-assisted contributions show a strong layer dependence due to the direct-to-indirect bandgap crossover. Electron-hole PL lifetime is limited by population transfer to lower-energy states and no dependence on the number of layers was observed. The lifetime of the defect-assisted recombination gets longer for thinner samples. Finally, we show that the PL lifetime decreases at high temperatures as a consequence of more efficient non-radiative recombinations.

Recent progress in contact, mobility, and encapsulation engineering of InSe and GaSe

“…5,16,19,[87][88][89] To date, it is the most used technique for producing high-quality InSe and GaSe layers. 11,18,74,[90][91][92] It involves repetitive peeling of the bulk crystal with the help of an adhesive tape until thin layers are obtained. 57,89 The tape containing the freshly cleaved flakes is adhered to an intermediate transfer polymer or directly onto the final substrate.…”

“…After the bandgap crossover, the VB takes the form of the Mexicanhat-like band structure (Figure 6A), with its maximum appearing only a few tens of milli electron-volt (meV) above the VB states at the Γ-point where the CBM is located. 56,90,129 For monolayer InSe, the direct bandgap lies $70 meV below the indirect bandgap of $2.39 eV. 18,56,129 In contrast to TMDCs, the much flatter Mexican-hatshaped dispersion in InSe allows the formation of a van Hove singularity as well as open possibilities of superconductivity and ferromagnetism upon hole-doping.…”

Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

“…In the case of InSe, the description of the obtained results is more complex, because the emission related to the B transition can not be measured directly. Moreover, we believe that the assumption that the temperature evolution of the B transition is similar to the optical band gap in InSe [44][45][46] may lead to misestimation. (1) intensity reflects the reported enhancement profile for this mode as a function of excitation energy in InSe in the vicinity of the B transition 30,47 .…”

Terahertz control of photoluminescence emission in few-layer InSe

“…After the initial thermalization and relaxation of the photo-excited carriers, a longliving PL emission is observed at 1.31 eV. The PL emission is assigned to a combination of defect-assisted radiative recombination and band-to-band recombination 25,26 . Figure 1(b) shows the PL decay integrated over the photon energy.…”

“…To verify this interpretation, we analyze the spectral shape of the PL emission as a function of time (shown in Figure 2(a) and 2(b)). We fit the spectrum at any time with a convolution of an Urbach tail U(E) ∝ exp( E E u ) with the electronic density of state D(E) ∝ Θ(E − E g ) where E u is the Urbach energy, E g is the band-gap energy, and Θ is the Heaviside step function 26,39 . The fitting function was then weighted with a Fermi-Dirac…”