Session 1

Young Hee Lee Director, Center for Integrated Nanostructure Physics (CINAP),

Institute for Basic Science (IBS), Department of Energy Science & Department of Physics

Sungkyunkwan University (SKKU), Suwon, Korea

Steven J. Koester Professor of Electrical and Computer Engineering, University of Minnesota

Two-dimensional (2D) materials are a family of layered crystalline materials characterized by strong in-plane bonds, but are attached only be weak van der Waals forces between layers. These characteristics allow 2D materials to be realized in single- and few-layer form. A wide range of 2D materials have been characterized recently, including graphene, transition metal dichalcogenides (TMDs), black phosphorus (BP) and numerous others. Few-layer BP is particularly interesting for numerous applications due to its high mobility, asymmetric effective mass and mobility, and tunable band gap from 0.3 to 1-2 eV. In this talk, I will present our recent results on high-performance BP FETs and photodetectors. Specifically, we have demonstrated BP n- and p-MOSFETs with record transconductance, and quantified the effect of crystal orientation on the device properties. We have also studied the limits of thickness and bias voltage on the subthreshold behavior in Schottky source/drain BP MOSFETs, and developed a method to improve the subthreshold slope and off-state current using electrostatically-doped contacts. These latter device structures have also recently been shown to allow the demonstration of tunneling FETs. Finally, we have demonstrated high-speed photodiodes in BP and made initial demonstrations of avalanche photodetectors in BP, which hold the promise to enable highly-sensitive imaging arrays operating across a wide spectral range.

Min-Kyu Joo CINAP, Institute for Basic Science (IBS), Sungkyunkwan University

Layered hexagonal boron nitride (h-BN) thin film has been reported as an exceptional dielectric substrate that prevails silicon oxide (SiO₂) for diverse optoelectronic applications in conjunction with other 2D layered materials such as graphene and transition metal dichalcogenides. However, the underlying mechanism of h-BN effect on metal-insulator phase transition, suppressed Coulomb scattering, and the reduced Schottky barrier is little known. In this seminar, we present a beneficial aspects of h-BN for carrier transport in 2D electronic system as an optimal dielectric. Various enhanced electrical properties of MoS₂/h-BN heterostructure over MoS₂/SiO₂ in terms of electron excess doping, activation energy, Schottky barrier height (SBH), and interface trap density are attributed to the inserted h-BN substrate which enables to mask the undesired effects of fixed oxide charges in SiO₂ and reduce interface trap density. The reduction of effective SBH in MoS₂/h-BN is ascribed to a higher energy band bending and dipole alignment effects compared to MoS₂/SiO₂. As a consequence, a four times enhanced field-effect mobility and three times reduced effective Schottky barrier height (SBH) in MoS₂/h-BN are achieved, allowing early observation of metal-insulator electronic phase transition at a much lower charge density of ~1.0 ´ 10¹² cm^–2 (T = 25K). These results will shed more light on the way to further performance enhancements in 2D electronic systems.

Mo Li Associate Professor of Electrical and Computer Engineering, University of Minnesota

I will discuss the application of black phosphorus for infrared optoelectronics. Efficient and fast photodetection in the near- and mid-infrared has been achieved through integration with silicon photonics. Optical modulation in the mid-infrared with black phosphorus has also been achieved through combined mechanisms of Pauli blocking and quantum-confined Franz-Keldysh effects. We have demonstrated the integration of black phosphorus with silicon photonics to achieve efficient photodetection in the near- and mid-infrared. Optical modulation in the mid-infrared with black phosphorus has also been achieved through combined mechanisms of Pauli blocking and quantum-confined Franz-Keldysh effects.