The linear dispersion relation in graphene gives rise to a surprising prediction: the resistivity due to isotropic scatterers, such as white-noise disorder or phonons, is independent of carrier density, n. Here we show that electron-acoustic phonon scattering is indeed independent of n, and contributes only 30 Omega to graphene's room-temperature resistivity. At a technologically relevant carrier density of 1 x1012 cm-2, we infer a mean free path for electron-acoustic phonon scattering of >2 microm and an intrinsic mobility limit of 2 x 105 cm2 V-1 s-1. If realized, this mobility would exceed that of InSb, the inorganic semiconductor with the highest known mobility ( approximately 7.7 x 104 cm2 V-1 s-1; ref. 9) and that of semiconducting carbon nanotubes ( approximately 1 x 105 cm2 V-1 s-1; ref. 10). A strongly temperature-dependent resistivity contribution is observed above approximately 200 K (ref. 8); its magnitude, temperature dependence and carrier-density dependence are consistent with extrinsic scattering by surface phonons at the SiO2 substrate and limit the room-temperature mobility to approximately 4 x 104 cm2 V-1 s-1, indicating the importance of substrate choice for graphene devices.

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Intrinsic and extrinsic performance limits of graphene devices on SiO2.

Heterostructures based on layering of two-dimensional (2D) materials such as graphene and hexagonal boron nitride represent a new class of electronic devices. Realizing this potential, however, depends critically on the ability to make high-quality electrical contact. Here, we report a contact geometry in which we metalize only the 1D edge of a 2D graphene layer. In addition to outperforming conventional surface contacts, the edge-contact geometry allows a complete separation of the layer assembly and contact metallization processes. In graphene heterostructures, this enables high electronic performance, including low-temperature ballistic transport over distances longer than 15 micrometers, and room-temperature mobility comparable to the theoretical phonon-scattering limit. The edge-contact geometry provides new design possibilities for multilayered structures of complimentary 2D materials.

One-dimensional electrical contact to a two-dimensional material.

Recent advances in nonsilica fiber technology have prompted the development of suitable materials for devices operating beyond 155 mu m The III-V ternaries and quaternaries (AlGaIn)(AsSb) lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices Consequently, there has been tremendous upthrust in research activities of GaSb-based systems As a matter of fact, this compound has proved to be an interesting material for both basic and applied research At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication This article presents an up to date comprehensive account of research carried out hitherto It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility An overview of the lattice, electronic, transport, optical and device related properties is presented Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as for device applications are addressed These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc Several avenues where further work is required in order to upgrade this III-V compound for optoelectronic devices are listed It is concluded that the present day knowledge in this material system is sufficient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication (C) 1997 American Institute of Physics

The physics and technology of gallium antimonide: An emerging optoelectronic material

Several research groups have been actively pursuing antimonide-based electronic devices in recent years. The advantage of narrow-bandgap Sb-based devices over conventional GaAs- or InP-based devices is the attainment of high-frequency operation with much lower power consumption. This paper will review the progress on three antimonide-based electronic devices: high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs). Progress on the HEMT includes the demonstration of Ka- and W-band low-noise amplifier circuits that operate at less than one-third the power of similar InP-based circuits. The RTDs exhibit excellent figures of merit but, like their InP- and GaAs-based counterparts, are waiting for a viable commercial application. Several approaches are being investigated for HBTs, with circuits reported using InAs and InGaAs bases.

Antimonide-based compound semiconductors for electronic devices: A review

We have developed a new superconducting digital technology, Reciprocal Quantum Logic, that uses ac power carried on a transmission line, which also serves as a clock. Using simple experiments, we have demonstrated zero static power dissipation, thermally limited dynamic power dissipation, high clock stability, high operating margins, and a low bit-error rate. These features indicate that the technology is scalable to far more complex circuits at a significant level of integration. On the system level, Reciprocal Quantum Logic combines the high speed and low-power signal levels of single-flux-quantum signals with the design methodology of semiconductor digital logic, including low static power dissipation, low latency combinational logic, and efficient device count.

Ultra-low-power superconductor logic

Quantum dots of InSb and GaSb were grown on GaAs(001) by molecular‐beam epitaxy. In situ scanning tunneling microscopy measurements taken after 1–2 monolayers of InSb or GaSb growth reveal the surface is a network of anisotropic ribbon‐like platelets. These platelets are a precursor to quantum dot growth. Transmission electron microscopy measurements indicate that the quantum dots are coherently strained. Quantum dots of InSb and GaSb capped by GaAs exhibit strong luminescence near 1.1 eV.

Self‐assembled InSb and GaSb quantum dots on GaAs(001)

Stranski-Krastanov growth of InSb, GaSb, and AlSb on GaAs: structure of the wetting layers

We discuss the molecular beam epitaxial growth of the random alloy InAsSb for use as the channel in high electron mobility transistors (HEMTs). Room-temperature mobilities of 22000cm2∕Vs have been achieved at a sheet carrier density of 1.4×1012∕cm2. This is a marked improvement over the mobility of 13000cm2∕Vs at the same carrier density obtained in previous attempts to grow the InAsSb channel using a digital alloy procedure [J. B. Boos, M. J. Yang, B. R. Bennett, D. Park, W. Kruppa, R. Bass, Electron. Lett. 35, 847 (1999)]. We have also implemented different barriers and buffer layers to enhance the transport properties and overall performance of the HEMT structure.

Growth of InAsSb-channel high electron mobility transistor structures

InAs/AlSb high electron mobility transistors (HEMTs) and resonant interband tunneling diodes (RITDs) with AlSb barriers and GaSb wells were grown in a single heterostructure by molecular beam epitaxy. The resulting HEMTs exhibit excellent dc and microwave performance at low drain voltages, with an intrinsic unity-current-gain cutoff frequency of 220 GHz. The RITD performance is comparable to RITDs grown directly on InAs substrates, with peak current densities above 104 A/cm2 and peak-to-valley ratios near 11 for 15 A AlSb barriers. The results represent an important step toward the fabrication of high-speed, low-power logic circuits in this material system.

R. Magno

Papers

Antimonide-based compound semiconductors for electronic devices: A review

Self‐assembled InSb and GaSb quantum dots on GaAs(001)

Stranski-Krastanov growth of InSb, GaSb, and AlSb on GaAs: structure of the wetting layers

Growth of InAsSb-channel high electron mobility transistor structures

Monolithic integration of resonant interband tunneling diodes and high electron mobility transistors in the InAs/GaSb/AlSb material system