Seongphill Moon

Surface transport and quantum Hall effect in ambipolar black phosphorus double quantum wells

Few-layer black phosphorus acts as tunable ambipolar wide quantum wells. Quantum wells (QWs) constitute one of the most important classes of devices in the study of two-dimensional (2D) systems. In a double-layer QW, the additional “which-layer” degree of freedom gives rise to celebrated phenomena, such as Coulomb drag, Hall drag, and exciton condensation. We demonstrate facile formation of wide QWs in few-layer black phosphorus devices that host double layers of charge carriers. In contrast to traditional QWs, each 2D layer is ambipolar and can be tuned into n-doped, p-doped, or intrinsic regimes. Fully spin-polarized quantum Hall states are observed on each layer, with an enhanced Landé g factor that is attributed to exchange interactions. Our work opens the door for using 2D semiconductors as ambipolar single, double, or wide QWs with unusual properties, such as high anisotropy.

Engineering Dirac materials: metamorphic InAs1-xSbx/InAs1-ySby superlattices with ultra-low bandgap

Quasiparticles with Dirac-type dispersion can be observed in nearly gapless bulk semiconductors alloys in which the bandgap is controlled through the material composition. We demonstrate that the Dirac dispersion can be realized in short-period InAs1-xSbx/InAs1-ySby metamorphic superlattices with the bandgap tuned to zero by adjusting the superlattice period and layer strain. The new material has anisotropic carrier dispersion: the carrier energy associated with the in-plane motion is proportional to the wave vector and characterized by the Fermi velocity vF, and the dispersion corresponding to the motion in the growth direction is quadratic. Experimental estimate of the Fermi velocity gives vF = 6.7 × 105 m/s. Remarkably, the Fermi velocity in this system can be controlled by varying the overlap between electron and hole states in the superlattice. Extreme design flexibility makes the short-period metamorphic InAs1-xSbx/InAs1-ySby superlattice a new prospective platform for studying the effects of charge-carrier chirality and topologically nontrivial states in structures with the inverted bandgaps.

Properties of novel metamorphic III-V materials with ultra-low bandgaps (Conference Presentation)

We present magnetooptical and transport properties of metamorphic periodic structures containing InAsSb layers with controllable modulated Sb composition [1]. The modulation period is determined by the thicknesses of the strain compensated InAsSbx/InAsSby pairs grown on a virtual AlGaInSb substrate with a lattice constant of 6.25 A. We demonstrate that the bandgap energy of ordered InAsSb0.3/InAsSb0.75 alloy varies from 100mev to a few meV as a result of the well-regulated variation of the modulation period from ∼3 to ∼7.5 nm. The material effective masses and the specific character of the energy spectra will be discussed. 1. G. Belenky, Y. Lin, L. Shterengas, D. Donetsky, G. Kipshidze and S. Suchalkin, Electron. Lett. 51 (19), 1521, (2015)