Showing papers by "Max C. Lemme published in 2011"

Gate-activated photoresponse in a graphene p-n junction.

Abstract: We study photodetection in graphene near a local electrostatic gate, which enables active control of the potential landscape and carrier polarity. We find that a strong photoresponse only appears when and where a p-n junction is formed, allowing on-off control of photodetection. Photocurrents generated near p-n junctions do not require biasing and can be realized using submicrometer gates. Locally modulated photoresponse enables a new range of applications for graphene-based photodetectors including, for example, pixilated infrared imaging with control of response on subwavelength dimensions.

Vertical Graphene Base Transistor

Abstract: We present a novel, graphene-based device concept for high-frequency operation: a hot electron graphene base transistor (GBT). Simulations show that GBTs have high current on/off ratios and high current gain. Simulations and small-signal models indicate that it potentially allows THz operation. Based on energy band considerations we propose a specific materials solution that is compatible with SiGe process lines.

Direct Graphene Growth on Insulator

Abstract: Fabrication of graphene devices is often hindered by incompatibility between the silicon technology and the methods of graphene growth. Exfoliation from graphite yields excellent films but is good ...

RF Performance Projections of Graphene FETs vs. Silicon MOSFETs

Abstract: A graphene field-effect-transistor (GFET) model calibrated with extracted device parameters and a commercial 65 nm silicon MOSFET model are compared with respect to their radio frequency behavior. GFETs slightly lag behind CMOS in terms of speed despite their higher mobility. This is counterintuitive, but can be explained by the effect of a strongly nonlinear voltage-dependent gate capacitance. GFETs achieve their maximum performance only for narrow ranges of VDS and IDS, which must be carefully considered for circuit design. For our parameter set, GFETs require at least {\mu} = 3000 cm2 V-1 s-1 to achieve the same performance as 65 nm silicon MOSFETs.

A Hysteresis-Free High-k Dielectric and Contact Resistance Considerations for Graphene Field Effect Transistors

Abstract: A Hysteresis-Free High-k Dielectric and Contact Resistance Considerations for Graphene Field Effect Transistors

Vertical Transistor with a Graphene Base

Abstract: We present a novel, graphene-based device concept for high-frequency operation: a hot electron graphene base transistor (GBT). Simulations show that GBTs have high current on/off ratios and high current gain. Simulations and small-signal models indicate that it potentially allows THz operation. Based on energy band considerations we propose a specific materials solution that is compatible with SiGe process lines.

Direct Graphene Growth on Insulator

Abstract: Fabrication of graphene devices is often hindered by incompatibility between the silicon technology and the methods of graphene growth. Exfoliation from graphite yields excellent films but is good mainly for research. Graphene grown on metal has a technological potential but requires mechanical transfer. Growth by SiC decomposition requires a temperature budget exceeding the technological limits. These issues could be circumvented by growing graphene directly on insulator, implying Van der Waals growth. During growth, the insulator acts as a support defining the growth plane. In the device, it insulates graphene from the Si substrate. We demonstrate planar growth of graphene on mica surface. This was achieved by molecular beam deposition above 600°C. High resolution Raman scans illustrate the effect of growth parameters and substrate topography on the film perfection. Ab initio calculations suggest a growth model. Data analysis highlights the competition between nucleation at surface steps and flat surface. As a proof of concept, we show the evidence of electric field effect in a transistor with a directly grown channel.

Graphene directly grown on SiO 2 -based insulators

Abstract: Strong effort is devoted to grow graphene directly on insulators to create a technological step towards cost effective mass production of high-frequency transistors on Si. We have shown recently, that direct graphene growth can be achieved on silicate substrates by solid carbon source deposition. Here, we present a study on the growth of graphene on insulator by means of Raman and photoelectron spectroscopy, corroborated by density functional theory calculations. We address temperature dependence and the correlation between graphene quality and the number of layers. We show that this approach may open a pathway to Si-compatible graphene growth for electronic applications.