研究目的
Investigating the valley Hall effect in monolayer WSe2 field-effect transistors, particularly in both n- and p-doping regimes, to understand spatial separation of carrier spin and valley polarization.
研究成果
The valley Hall effect is observed in monolayer WSe2 transistors for both n- and p-doping, with spatial mapping showing spin-valley polarization at channel edges. A spin accumulation of 44 spins/μm is deduced in the p-doped regime, with an inferred spin lifetime lower bound of 0.4 ns. The results align with a drift-diffusion model, suggesting potential for higher spin accumulations with improved samples. This is the first observation of the VHE in the p-doped regime, enabling future studies at higher temperatures due to large valence band spin-splitting.
研究不足
The study is conducted at low temperature (20 K), limiting applicability to room temperature. Device mobilities are lower than ideal due to contact resistance and lack of encapsulation, potentially underestimating true values. The spin diffusion length is inferred to be short, and photodoping effects may influence results.
1：Experimental Design and Method Selection:
The study uses optical Kerr rotation measurements to probe the valley Hall effect in monolayer WSe2 transistors at 20 K. A drift-diffusion model is employed to analyze spin accumulation.
2：Sample Selection and Data Sources:
Monolayer WSe2 field-effect transistors are fabricated with Pd contacts on a SiO2/Si substrate. Data are collected from electrical and optical measurements.
3：List of Experimental Equipment and Materials:
Equipment includes a liquid-helium cooled cryostat, lock-in amplifier, laser sources (700 nm and 730 nm wavelengths), and optical setup for Kerr rotation. Materials include WSe2 monolayer, Pd films, Si back-gate, and SiO2 dielectric.
4：Experimental Procedures and Operational Workflow:
Devices are characterized electrically (JD vs VGS) and optically (Kerr rotation scans across the channel) under varying gate and drain voltages. Measurements are performed at 20 K with AC bias.
5：Data Analysis Methods:
Data are analyzed using a dielectric function model for optical properties, a capacitor model for charge density estimation, and a drift-diffusion model for spin accumulation.
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