Laurent Syavoch Bernard

Microengineered CH3NH3PbI3 Nanowire/Graphene Phototransistor for Low‐Intensity Light Detection at Room Temperature

The first hybrid phototransistors are reported where the performance of a network of photoactive CH3NH3PbI3 nanowires is enhanced by CVD-grown monolayer graphene. These devices show responsivities as high as ≈2.6 × 106 A W-1 in the visible range, showing potential as room-temperature single-electron detectors.

Room-Temperature Negative Differential Resistance in Graphene Field Effect Transistors: Experiments and Theory

In this paper we demonstrate experimentally and discuss the negative differential resistance (NDR) in dual-gated graphene field effect transistors (GFETs) at room temperature for various channel lengths, ranging from 200 nm to 5 μm. The GFETs were fabricated using chemically vapor-deposited graphene with a top gate oxide down to 2.5 nm of equivalent oxide thickness (EOT). We originally explain and demonstrate with systematic simulations that the onset of NDR occurs in the unipolar region itself and that the main mechanism behind NDR is associated with the competition between the specific field dependence of carrier density and the drift velocity in GFET. Finally, we show experimentally that NDR behavior can still be obtained with devices of higher EOTs; however, this comes at the cost of requiring higher bias values and achieving lower NDR level.

Graphene Negative Differential Resistance Circuit With Voltage-Tunable High Performance at Room Temperature

We propose, fabricate, and experimentally demonstrate a circuit based on graphene field-effect transistors (GFETs) showing enhanced negative differential resistance (NDR) characteristics at room temperature. The proposed graphene NDR (GNDR) circuit consists of three GFETs, which includes a two GFET inverter connected in a feedback loop with the main GFET in which the NDR is realized. Herein, a GNDR circuit is demonstrated using large-area chemical vapor deposition grown graphene and no doping step, which makes it compatible with silicon-based circuits. The circuit shows negative differential conductance (2.1 mS/μm) that is almost an order of magnitude better than NDR based on 1-GFET. This conductance level is uniquely tunable (×2.3) with the supply voltage as well as with the back bias voltage. It also exhibits an improved peak-to-valley current ratio (2.2) and a wide voltage range (0.6 V) over which NDR is valid. In comparison with other NDR technologies, the GNDR has a very high peak-current-density of the order of 1 mA/μm , which offers unique opportunities for designing circuits for applications requiring high current drive.

Reflection amplifier based on graphene

While RF transistor amplifiers—such as the field effect transistor (FET) amplifier which leverages its transconductance for amplification—are the key enablers of signal amplification in todays wireless communication; their ability to provide amplification degrades with increasing frequencies, thereby requiring multiple amplification stages which makes the device noisy, expensive and bigger in size. Owing to their broadband amplification capabilities, reflection-type amplifiers based on negative differential resistance (NDR) devices provide means to overcome these limitations. Herein, we propose a novel reflection amplifier circuit consisting of three graphene FETs (GFETs) which leverages its unique NDR characteristics. We show through rigorous simulation and modeling that broadband amplification exceeding several hundreds of GHz should be possible for the scaled graphene circuit. In addition, both the gain and frequency of operation can be highly modulated by varying the bias in the NDR region. Finally, we provide an experimental evidence of reflection amplification in the proposed circuit.

Graphene negative differential resistance (GNDR) circuit with enhanced performance at room temperature

We propose and experimentally demonstrate a novel circuit based on graphene FETs (GFETs) showing excellent negative differential resistance (NDR) characteristics at room temperature. The proposed GNDR circuit exploits a closed loop connection of 1-GFET with a 2-GFET inverter, being highly scalable. The circuit is demonstrated using large-area chemical vapor deposition grown graphene and no doping step, which makes it compatible with silicon-based circuits. It exhibits improved peak-to-valley current ratio (PVCR), higher NDR level and wider voltage range over which NDR is valid, as compared to any previous graphene NDR. The NDR is uniquely tunable with the supply voltage as well as with back bias voltage. We show that PVCR of up to 2 can be achieved. In comparison to other NDR technologies, the graphene NDR has a high peak-current-density of the order of 1 mA/μm, which offers opportunities for designing circuits with high current drive.

Photodetectors: Microengineered CH3NH3PbI3 Nanowire/Graphene Phototransistor for Low-Intensity Light Detection at Room Temperature (Small 37/2015)

E. Horváth and co-workers report the first hybrid phototransistors where the performance of a network of photoactive organometal halide perovskite nanowires (methylammonium lead iodide - MAPbI3 ) is enhanced by CVD-grown monolayer graphene. On page 4824, these microfabricated devices show responsivities as high as 2.6 × 10(6) A W(-1) in the visible range. The dramatic enhancement of the responsivity at very low light intensities (pW) suggests the use of MAPbI3 nanowire/graphene devices as lowlight imaging sensors and single photon detectors.