TY - JOUR
T1 - Valley relaxation of resident electrons and holes in a monolayer semiconductor
T2 - Dependence on carrier density and the role of substrate-induced disorder
AU - Li, Jing
AU - Goryca, M.
AU - Yumigeta, K.
AU - Li, H.
AU - Tongay, S.
AU - Crooker, S. A.
N1 - Publisher Copyright:
© 2021 American Physical Society.
PY - 2021/4
Y1 - 2021/4
N2 - Using time-resolved optical Kerr rotation, we measure the low-temperature valley dynamics of resident electrons and holes in exfoliated WSe2 monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically gated WSe2 monolayers having different dielectric environments. In a fully encapsulated structure (hBN/WSe2/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time τv is quite long (∼10μs) at low carrier densities, but decreases rapidly to less than 100 ns at high electron or hole densities â‰2×1012cm-2. In contrast, in a partially encapsulated WSe2 monolayer placed directly on silicon dioxide (hBN/WSe2/SiO2), carrier valley relaxation is multiexponential at low carrier densities. The difference is attributed to environmental disorder from the SiO2 substrate. Unexpectedly, very small out-of-plane magnetic fields can increase τv, especially in the hBN/WSe2/SiO2 structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition-metal dichalcogenide semiconductors.
AB - Using time-resolved optical Kerr rotation, we measure the low-temperature valley dynamics of resident electrons and holes in exfoliated WSe2 monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically gated WSe2 monolayers having different dielectric environments. In a fully encapsulated structure (hBN/WSe2/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time τv is quite long (∼10μs) at low carrier densities, but decreases rapidly to less than 100 ns at high electron or hole densities â‰2×1012cm-2. In contrast, in a partially encapsulated WSe2 monolayer placed directly on silicon dioxide (hBN/WSe2/SiO2), carrier valley relaxation is multiexponential at low carrier densities. The difference is attributed to environmental disorder from the SiO2 substrate. Unexpectedly, very small out-of-plane magnetic fields can increase τv, especially in the hBN/WSe2/SiO2 structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition-metal dichalcogenide semiconductors.
UR - http://www.scopus.com/inward/record.url?scp=85104882588&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85104882588&partnerID=8YFLogxK
U2 - 10.1103/PhysRevMaterials.5.044001
DO - 10.1103/PhysRevMaterials.5.044001
M3 - Article
AN - SCOPUS:85104882588
SN - 2475-9953
VL - 5
JO - Physical Review Materials
JF - Physical Review Materials
IS - 4
M1 - 044001
ER -