Photoluminescence dynamics in few-layer InSe

We study the optical properties of thin flakes of InSe encapsulated in hBN. More specifically, we investigate the photoluminescence (PL) emission and its dependence on sample thickness and temperature. Through the analysis of the PL lineshape, we discuss the relative weights of the exciton and electron-hole contributions. Thereafter we investigate the PL dynamics. Two contributions are distinguishable at low temperature: direct bandgap electron-hole and defect-assisted recombination. The two recombination processes have lifetime of τ1 ∼ 8 ns and τ2 ∼ 100 ns, respectively. The relative weights of the direct bandgap and defect-assisted contributions show a strong layer dependence due to the direct-to-indirect bandgap crossover. Electron-hole PL lifetime is limited by population transfer to lower-energy states and no dependence on the number of layers was observed. The lifetime of the defect-assisted recombination gets longer for thinner samples. Finally, we show that the PL lifetime decreases at high temperatures as a consequence of more efficient non-radiative recombinations

Electrical characterization of multi-gated WSe2/MoS2 van der Waals heterojunctions

Abstract Vertical stacking of different two-dimensional (2D) materials into van der Waals heterostructures exploits the properties of individual materials as well as their interlayer coupling, thereby exhibiting unique electrical and optical properties. Here, we study and investigate a system consisting entirely of different 2D materials for the implementation of electronic devices that are based on quantum mechanical band-to-band tunneling transport such as tunnel diodes and tunnel field-effect transistors. We fabricated and characterized van der Waals heterojunctions based on semiconducting layers of WSe2 and MoS2 by employing different gate configurations to analyze the transport properties of the junction. We found that the device dielectric environment is crucial for achieving tunneling transport across the heterojunction by replacing thick oxide dielectrics with thin layers of hexagonal-boronnitride. With the help of additional top gates implemented in different regions of our heterojunction device, it was seen that the tunneling properties as well as the Schottky barriers at the contact interfaces could be tuned efficiently by using layers of graphene as an intermediate contact material

Data: Fully encapsulated and stable black phosphorus field-effect transistors

Fabricated devices went through electrical characterization with 4200-SCS parameter analyzer located in greyroom and Agilent 4156C Parameter Analyzer equipped with a cool-down setup located in 613. The measured data was processed with origin software

Novel Mixed-Dimensional hBN-Passivated Silicon Nanowire Reconfigurable Field Effect Transistors: Fabrication and Characterization

This work demonstrates the novel concept of a mixed-dimensional reconfigurable field effect transistor (RFET) by combining a one-dimensional (1D) channel material such as a silicon (Si) nanowire with a two-dimensional (2D) material as a gate dielectric. An RFET is an innovative device that can be dynamically programmed to perform as either an n- or p-FET by applying appropriate gate potentials. In this work, an insulating 2D material, hexagonal boron nitride (hBN), is introduced as a gate dielectric and encapsulation layer around the nanowire in place of a thermally grown or atomic-layer-deposited oxide. hBN flake was mechanically exfoliated and transferred onto a silicon nanowire-based RFET device using the dry viscoelastic stamping transfer technique. The thickness of the hBN flakes was investigated by atomic force microscopy and transmission electron microscopy. The ambipolar transfer characteristics of the Si-hBN RFETs with different gating architectures showed a significant improvement in the device’s electrical parameters due to the encapsulation and passivation of the nanowire with the hBN flake. Both n- and p-type characteristics measured through the top gate exhibited a reduction of hysteresis by 10–20 V and an increase in the on–off ratio (ION/IOFF) by 1 order of magnitude (up to 108) compared to the values measured for unpassivated nanowire. Specifically, the hBN encapsulation provided improved electrostatic top gate coupling, which is reflected in the enhanced subthreshold swing values of the devices. For a single nanowire, an improvement up to 0.97 and 0.5 V/dec in the n- and p-conduction, respectively, is observed. Due to their dynamic switching and polarity control, RFETs boast great potential in reducing the device count, lowering power consumption, and playing a crucial role in advanced electronic circuitry. The concept of mixed-dimensional RFET could further strengthen its functionality, opening up new pathways for future electronics

Power Integrity Challenges in Large Scale Quantum Computers and Solutions

The ICs belonging to a quantum computer need stable and regulated supply voltages for proper operation, e.g. the phase noise of RF oscillators is dependent on their power supply quality. Moreover, the power supply needs of a large scale QC will be challenging to satisfy by simply using supply lines connecting the ICs inside the cryostat with the power sources at room temperature. This is because voltage ripples (e.g. pulse tube vibration induced noise), ground loops induced noise and dynamic load currents may affect the ICs supply lines and compromise the QC power integrity. Furthermore, it is expected that the connection lines available in large scale QCs be scarce due to the limited cryostat space. Therefore, the usage of several lines to set different supply domains may not be possible and be a restricting factor for the QCs scalability.This presentation will address the cryogenic power integrity topic by providing:— A review of the power integrity challenges faced by cryogenic ICs. — Solution approaches focused on the cryogenic setup and the use of cryogenic voltage regulators. — Cryogenic characterization and modelling of FDSOI technology (22 nm) for ICs design. — Design and test of cryogenic voltage references, based on cryogenic Vth saturation and Vth difference. — Design and test of a cryogenic voltage regulator. — Design of Digital LDOs for cryogenic applications. — An application case: cryogenic voltage regulator applied to power the reference circuit of a cryogenic DAC used for the DC voltage setting of a Single Electron Transistor Quantum Do

Data for: Photoluminescence dynamics in few-layer InSe

We study the optical properties of thin flakes of InSe encapsulated in hexagonal boron nitride. Mores pecifically, we investigate the photoluminescence (PL) emission and its dependence on sample thickness and temperature. Through the analysis of the PL line shape, we discuss the relative weights of the exciton and electron-hole contributions. Thereafter we investigate the PL dynamics. Two contributions are distinguishable at low temperature: direct band-gap electron-hole and defect-assisted recombination. The two recombination processes have lifetimes ofτ1∼8ns andτ2∼100 ns, respectively. The relative weights of the direct band-gap and defect-assisted contributions show a strong layer dependence due to the direct-to-indirect band-gap crossover. Electron-hole PL lifetime is limited by population transfer to lower-energy states and no dependence on the number of layers was observed. The lifetime of the defect-assisted recombination gets longer for thinner samples. Finally, we show that the PL lifetime decreases at high temperatures as a consequence of more efficient nonradiative recombinations

Photoluminescence dynamics in few-layer InSe

We study the optical properties of thin flakes of InSe encapsulated in hexagonal boron nitride. More specifically, we investigate the photoluminescence (PL) emission and its dependence on sample thickness and temperature. Through the analysis of the PL line shape, we discuss the relative weights of the exciton and electron-hole contributions. Thereafter we investigate the PL dynamics. Two contributions are distinguishable at low temperature: direct band-gap electron-hole and defect-assisted recombination. The two recombination processes have lifetimes of tau(1)similar to 8 ns and tau(2) similar to 100 ns, respectively. The relative weights of the direct bandgap and defect-assisted contributions show a strong layer dependence due to the direct-to-indirect band-gap crossover. Electron-hole PL lifetime is limited by population transfer to lower-energy states and no dependence on the number of layers was observed. The lifetime of the defect-assisted recombination gets longer for thinner samples. Finally, we show that the PL lifetime decreases at high temperatures as a consequence of more efficient nonradiative recombinations

Enhanced Trion Emission in Monolayer MoSe2 by Constructing a Type-I Van Der Waals Heterostructure

Funding Information: J.M.D. thanks China Scholarship Council (File no. 201706890037). L.H. thanks the National Natural Science Foundation of China (project number 61804098) and the Zhejiang Provincial Natural Science Foundation of China (project number LZ21E020002). Y.J.Z. thanks the Shenzhen Science and Technology Project under Grant no. JCYJ20180507182246321. A.V.K. also thanks the DFG for support within the projects KR 4866/2‐1 (project number 339 406129719). The computational support from the Technical University of Dresden computing cluster (TAURUS) and from High Performance Computing Center (HLRS) in Stuttgart, Germany is gratefully appreciated. The authors thank Scheumann for the metal deposition of the substrates. The nanofabrication facilities (NanoFaRo) at the Ion Beam Center at the HZDR are also gratefully acknowledged. Publisher Copyright: © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbHTrions, quasi-particles consisting of two electrons combined with one hole or of two holes with one electron, have recently been observed in transition metal dichalcogenides (TMDCs) and drawn increasing attention due to potential applications of these materials in light-emitting diodes, valleytronic devices as well as for being a testbed for understanding many-body phenomena. Therefore, it is important to enhance the trion emission and its stability. In this study, a MoSe2/FePS3 van der Waals heterostructure (vdWH) with type-I band alignment is constructed, which allows for carriers injection from FePS3 to MoSe2. At low temperatures, the neutral exciton (X0) emission in this vdWH is almost completely suppressed. The ITrion/Ix0 intensity ratio increases from 0.44 in a single MoSe2 monolayer to 20 in this heterostructure with the trion charging state changing from negative in the monolayer to positive in the heterostructure. The optical pumping with circularly polarized light shows a 14% polarization for the trion emission in MoSe2/FePS3. Moreover, forming such type-I vdWH also gives rise to a 20-fold enhancement of the room temperature photoluminescence from monolayer MoSe2. These results demonstrate a novel approach to convert excitons to trions in monolayer 2D TMDCs via interlayer doping effect using type-I band alignment in vdWH.Peer reviewe