Layered III-VI chalcogenide semiconductor crystals for radiation detectors

Mandal, Krishna C.; Mërtiri, Alket; Pabst, Gary W.; Roy, Ronald G.; Cui, Yunlong; Battacharya, P.; Groza, Michael; Bürger, A.; Conway, A. M.; Nikolić, Rebecca J.; Nelson, A. J.; Payne, Stephen A.

doi:10.1117/12.796235

Cited by 8 publications

(3 citation statements)

References 19 publications

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“…Sample preparation. GaSe nanoslabs are mechanically exfoliated from a Bridgman grown GaSe crystal 37 and deposited onto a 90-nm SiO 2 /Si substrate. The samples studied in this study are mainly the modifications.…”

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Linearly Polarized Remote-Edge Luminescence in GaSe Nanoslabs

et al. 2015

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We report highly linearly polarized remote luminescence that emerges at the cleaved edges of nanoscale gallium selenide slabs tens of micrometers away from the optical excitation spot. The remote-edge luminescence (REL) measured in the reflection geometry has a degree of linear polarization above 0.90, with polarization orientation pointing toward the photoexcitation spot. The REL is dominated by an index-guided optical mode that is linearly polarized along the crystalline c-axis. This luminescence is from out-of-plane dipoles that are converted from in-plane dipoles through a spin-flip process at the excitation spot.

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confidence: 99%

Linearly Polarized Remote-Edge Luminescence in GaSe Nanoslabs

et al. 2015

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“…Experiment. Nanometer thick GaSe crystals are mechanically exfoliated from a Bridgman-grown crystal with unintentionally p-doped concentration 10 14 − 10 15 cm −3 [33] and deposited onto a silicon substrate with a 90 nm SiO 2 layer. Sample thickness is measured by atomic force microscopy.…”

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Optical and spin polarization dynamics in GaSe nanoslabs

et al. 2015

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We report nearly complete preservation of "spin memory" between optical absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with 0.2 eV excess energy. At cryogenic temperatures, the initial degree of circular polarization (ρ0) of PL approaches unity, with the major fraction of the spin polarization decaying with a time constant >500 ps in sub-100-nm GaSe nanoslabs. Even at room temperature, ρ0 as large as 0.7 is observed, while pumping 1 eV above the band edge yields ρ0 = 0.15. Angular momentum preservation for both electrons and holes is due to the separation of the non-degenerate conduction and valence bands from other bands. In contrast to valley polarization in atomically thin transition metal dichalcogenides, here optical spin polarization is preserved in nanoslabs of 100 layers or more of GaSe.Solid-state systems exhibiting high spin polarization and long spin relaxation time are desirable for spintronic applications. Various semiconductors have been studied for creation of long-lived non-equilibrium spin populations and coherences [1][2][3][4] . The most extensively studied system is gallium arsenide (GaAs). However, optically pumped electron spin polarization is limited to 1/2, while the maximal degree of circular polarization of photoluminescence is 1/4 1,3 , owing to the degenerate heavy-and light-hole valence bands and sub-ps hole spin relaxation. Doping 5 or quantum confinement 6 has been used to quench electron spin relaxation. Unity electron spin polarization can be achieved in heterostructures where heavy-and light-hole energy degeneracy is lifted by quantum confinement or strain. Still, nearresonant optical excitation is necessary to avoid transitions involving both heavy-and light-hole bands. In analogy to spin polarization, valley polarization has been demonstrated in monolayer transition metal dichalcogenides (TMDs) with potential applications exploiting both spin and valley degrees of freedom.In monolayer TMDs with broken inversion symmetry, a direct gap emerges at the corners (K points) of the Brillouin zone, enabling valley-dependent inter-band transitions under circularly polarized optical excitation 7-9 . Furthermore, the substantial spin-splitting of valence bands at the band edges due to spin-orbit interaction originating from the d orbitals of TM ions has led to recent reports of long hole spin and valley lifetimes 10,11 , valley exciton polarization and coherence 12,13 , circularly polarized electroluminescence 14 , and valley Hall effect 15 . Indeed, circularly polarized PL was observed in single-and bi-layer TMDs 8,9,11-13 with steady-state near-resonant circularly polarized excitation. However, time-and polarization-resolved PL measurements suggest that, at least in MoS 2 , circularly polarized PL can result from sub-10-ps recombination and valley (spin) lifetimes rather than an intrinsically long-lived valley or hole spin polarization 8,16,17 . Additionally, emission at the direct gap becomes dominant only at the monolayer level [18][19][20] .Here, we demonstr...

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“…Sample preparation and experimental measurement methods were described previously 12 . Thin films of GaSe crystals were mechanically exfoliated from a Bridgmangrown crystal 26 and deposited onto a silicon substrate with a 90 nm SiO 2 layer, with the thickness measured using atomic force microscopy. Samples were mounted in vacuum on a copper cold finger attached to an optical liquid helium flow cryostat for all experiments.…”

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confidence: 99%

Exciton spin dynamics in GaSe

Tang

Xie

Mandal

et al. 2015

Journal of Applied Physics

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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

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Layered III-VI chalcogenide semiconductor crystals for radiation detectors

Cited by 8 publications

References 19 publications

Linearly Polarized Remote-Edge Luminescence in GaSe Nanoslabs

Linearly Polarized Remote-Edge Luminescence in GaSe Nanoslabs

Optical and spin polarization dynamics in GaSe nanoslabs

Exciton spin dynamics in GaSe

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