Low frequency Raman spectroscopy of few-atomic-layer thick hBN crystals

International audienc

Contact gating at GHz frequency in graphene

International audienceThe paradigm of graphene transistors is based on the gate modulation of the channel carrier density by means of a local channel gate. This standard architecture is subject to the scaling limit of the channel length and further restrictions due to access and contact resistances impeding the device performance. We propose a novel design, overcoming these issues by implementing additional local gates underneath the contact region which allow a full control of the Klein barrier taking place at the contact edge. In particular, our work demonstrates the GHz operation of transistors driven by independent contact gates. We benchmark the standard channel and novel contact gating and report for the later dynamical transconductance levels at the state of the art. Our finding may find applications in electronics and optoelectronics whenever there is need to control independently the Fermi level and the electrostatic potential of electronic sources or to get rid of cumbersome local channel gates

Lifetime assessment in crystalline silicon: From nanopatterned wafer to ultra-thin crystalline films for solar cells

International audienc

RF-Quantum Capacitance of the Topological Insulator Bi 2 Se 3 in the Bulk Depleted Regime

International audienceA metal-dielectric topological-insulator capacitor device based on hexagonal-boron-nitrate-(h-BN) encapsulated CVD-grown Bi 2 Se 3 is realized and investigated in the radio-frequency regime. The rf quantum capacitance and device resistance are extracted for frequencies as high as 10 GHz and studied as a function of the applied gate voltage. The superior quality h-BN gate dielectric combined with the optimized transport characteristics of CVD-grown Bi 2 Se 3 (n ∼ 10 18 cm −3 in 8 nm) on h-BN allow us to attain a bulk depleted regime by dielectric gating. A quantum-capacitance minimum and a linear variation of the capacitance with the chemical potential are observed revealing a Dirac regime. The topological surface state in proximity to the gate is seen to reach charge neutrality, but the bottom surface state remains charged and capacitively coupled to the top via the insulating bulk. Our work paves the way toward implementation of topological materials in rf devices

RF compressibility of topological surface and interface states in metal–hBN–Bi 2 Se 3 capacitors

International audienc

Nanophotonics for ultrathin crystalline silicon photovoltaics: When photons (actually) meet electrons

22-26 septInternational audienceno abstrac