Exciton spin dynamics in GaSe

Abstract

We analyze exciton spin dynamics in GaSe under nonresonant circularly polarized optical pumping with an exciton spin-flip rate-equation model. The model reproduces polarized time-dependent photoluminescence measurements in which the initial circular polarization approaches unity even when pumping with 0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a biexponential decay with a sub-20 ps and a >500 ps time constants, which are also reproduced by the rate-equation model assuming distinct spin-relaxation rates for hot (nonequilibrium) and cold band-edge excitons.Comment: 8 pages, 6 figure

Symmetry, distorted band structure, and spin-orbit coupling of group-III metal-monochalcogenide monolayers

“…This dynamic upper valence band hole polarization can be modeled via a rate-equation approach, similar to the simulation of recent time-resolved luminescence studies in thin but still 3D GaSe flakes. 37,38 A simplified equivalent three-level system is shown in Fig. 7(a), where spin-conserving interband transitions (Γ − 3 ↔ Γ − 2 optical orientation with generation rate constant G ↑ and spontaneous relaxation rate constant R ± , and Γ + 1 → Γ − 2 bandgap radiative relaxation with rate constant R z ) appear in solid arrows, while spin-mixing intraband spin relaxation (with timescales τ c,v, for conduction, valence and lower-valence bands, respectively, indicated by subscripts) appears in dashed arrows.…”

“…35,36 Circularly polarized photoluminescence reveals spin dynamics in nanoslabs. 37,38 In some cases, monolayer M X can even be synthesized epitaxially on silicon 39 or non-epitaxially on insulating substrates such as SiO 2 via vapor phase deposition, with quality that rivals exfoliated material. 40,41 Despite this recent explosion of experimental results with monolayer M X, the theoretical establishment has relied almost exclusively on sophisticated ab initio methods to model electronic structure.…”

Solution‐Processed GaSe Nanoflake‐Based Films for Photoelectrochemical Water Splitting and Photoelectrochemical‐Type Photodetectors

“…The most common one is the hexagonal ε‐GaSe (space symmetry group: Pm‐), which is grown by Bridgman methods . Due to its structure, GaSe shows fascinating optoelectronic properties, including photoresponse in ultraviolet–visible (UV–vis) spectral range (from 1.8 to 5 eV), nonlinear optical behavior, and a distinctive spin physics (e.g., spin‐orbit coupling effects and generation/retention of spin polarization under nonresonant optical pumping). For the aforementioned properties, GaSe has been proposed for photodetectors with high responsivity (e.g., up to values > 1000 A W −1 at light intensity ≤ 0.1 mW cm −2 , in heterojunction with graphene), nonlinear frequency generation (e.g., second and third harmonic and ultrabroadband radiation generation), spin polarization control (e.g., spintronic logic devices), light‐emitting devices, optical microcavities, and saturable absorbers .…”

Oxidation dynamics of ultrathin GaSe probed through Raman spectroscopy

“…Its bulk band gap of 2.12 eV 2,11 is predicted to increase to more than 3.5 eV for the monolayer 12,13 . Atomically thin flakes and devices have shown a high photoresponse 9,14 , a composition tunable band gap 15 , near-unity optical polarization 16 , the strongest second-harmonic generation observed in a monolayer 2D material 17,18 , and transistors with high ON/OFF ratios 19 . Like most 2D materials, the properties of GaSe are expected to sensitively depend on the interaction of its surface with its chemical environment.…”