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Quantum Transport Properties of Atomically Thin Black Phosphorus

  • Author(s): Gillgren, Nathaniel
  • Advisor(s): Lau, Chun Ning (Jeanie)
  • et al.
Abstract

Since the discovery of graphene, two-dimensional (2D) van der Waals materials research has flourished, with new crystals and novel phenomena discovered at a rapid pace. In 2014, black phosphorus (BP) was rediscovered as a member of 2D materials, displaying high quality electronic transport with in-plane anisotropy, though the first generation of layered devices suffered from poor stability and relatively low mobility. In this thesis, we overcome these challenges by employing van der Waals assembly techniques to create BP devices sandwiched between thin hexagonal boron nitride layers. These devices are air-stable, for more than two weeks, and boast mobility up to 500 cm2V-1s-1 at room temperature and 4,000 cm2V-1s-1 at low temperature. Using two-point and four-point geometries with global and local gates, we observe Shubnikov de Haas oscillations that yield effective mass of holes ~0.25 me to 0.31 me, where me is the mass of the electron. From weak localization measurements, we obtain phase relaxation length of ~30 nm to 100 nm. Moreover, we determine mobility bottleneck and transport mechanism from temperature dependence measurements: when the device is highly hole doped, the mobility µ exhibits power law dependence on temperature T, µ ~ T0.6, suggesting that it is limited by charged impurity scattering; close to the band edge, conduction is dominated by variable range hopping, with estimated localization length ~ 1.7 nm – 30 nm. The studies presented here contributed to our understanding of electronic properties of atomically thin BP, and will help to guide future efforts in fabrication, exploring, and engineering devices based on 2D semiconductors.

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