The Nanotechnology Section (Code 6876) performs both basic and applied research in areas that have potential impact on electronics technology for the Navy, Marine Corps, and other components of the Department of Defense. Areas of research include MBE growth and characterization of antimonide-based compound semiconductors for low-power high-electron mobility transistors, p-channel field-effect transistors, heterojunction bipolar transistors, hetero-barrier varactors, and mm-wave diodes; carbon nanotubes for chemical detection; graphene for electronics; surface-enhanced Raman spectroscopy from nanowires for chemical sensing; UHV surface science; surface infrared spectroscopy; quantum-chemical modeling of chemical warfare agents and simulants; and gold nanocluster chemiresistor sensors. For more information, send email to the section head.

Current Areas of Research

InAs-Channel High-Electron-Mobility Transistors (HEMTs)

The Electronic Materials Branch, in collaboration with the Microwave Technology Branch, Code 6850, is investigating HEMTs with InAs channels and AlGaSb barriers. Advantages of this material system include the high electron mobility (30,000 cm2/V-s) and velocity (4 x 107 cm/s) of InAs, and a large conduction band offset between InAs and AlGaSb (1.3 eV). As a result, single quantum wells of InAs clad by AlGaSb are of interest for application to high-speed, low-voltage HEMTs. Promising HEMT characteristics have been achieved, with an intrinsic unity-current-gain cut-off frequency, fT, of 90 GHz at a drain-source voltage of only 100 mV for a 0.1 µm gate length.

(In)GaSb p-channel Field-Effect Transistors

NRL has been the leader in developing n-channel, Sb-based field-effect transistors (FETs). Amplifier circuits have been demonstrated in the S-band, X-band, and W-band with several times lower power consumption than conventional GaAs- or InP-based circuits. Sb-based complementary circuits are needed for a variety of digital logic applications. This technology will require p-channel FETs with high hole mobility. We applied band-structure engineering to enhance hole mobility in compound semiconductors. Quantum wells of InGaSb clad with AlGaSb were grown with compressive strain to split the degenerate heavy- and light-hole bands, resulting in lower effective mass and higher hole mobility.

Antimonide-based Heterojunction Bipolar Transistor

The goal of this work, that is carried out in collaboration with Code 6853 the High Speed / Low power Devices Section, is to make significant improvements in both speed and power by the development of HBTs composed of InAs, GaSb, AlSb and their ternary and quaternary alloys with a lattice constant between 6.2 and 6.3 Å. Estimates indicate that with these materials it is possible to realize devices operating up to four times faster at one tenth the power of those currently available in the InP and GaAs material systems. These improvements stem from the high electron and hole mobilities available in the InAs/GaSb/AlSb system and from the small bandgaps that allow low voltage operation. The availability of a wide assortment of conduction band and valence band offsets allows the use of bandgap engineering to optimize device performance.

Heterostructure Barrier Varactors

A heterostructure barrier varactor is an electronic device that can be used in a circuit like that shown in the figure to produce small amounts of power at THz frequencies. The device needs a bias dependent capacitance, C, that is symmetric with respect to bias polarity along with a high resistance. The single barrier structure also shown in the figure accomplishes this as the high potential barrier acts to block the current flow, and the depletion layers in the InAs on either side of the barrier produce the bias dependent capacitance. Code 6853, the High Speed / Low power Devices Section, has fabricated HBVs and made current-voltage, and S-parameter measurements on them.

Low-Power pN THz Mixer Diode

Mixer diodes operating at THz frequencies are needed for use in imaging arrays, communication devices and in spectroscopic systems for the detection of chemical and biological agents. An example of a circuit using a mixer in an anti-parallel pair geometry is illustrated in the figure. In an array, many pairs of diodes would need to be driven by the local oscillator source, and a highly complicated set of wires would be required to route the signals. It is desirable to make these systems lightweight and small to be hand carried or used in a satellite.

The properties of bilayer graphene films depend on the relative orientation or twist of the two layers. A dramatic effect of this angular dependence is shown above, where two stacked polycrystalline graphene films have a patchwork of colored regions that appear red, blue, or yellow. This ‘stained-glass’ window appearance arises from the emergence of a narrow absorption band due to direct electronic coupling between the layers. Graphene and Other 2D Materials

We are investigating the sensor properties of carbon nanotubes. Recent work has resulted in CNT sensors capable of detecting chemical vapors at concentrations (sub-ppb) far below the performance of commercial solid-state sensors. This performance level has been achieved by systematically identifying and addressing the key scientific and technological problems, which include high-yield CNT device fabrication, the physics of CNT/molecule interactions, optimal signal transduction and noise reduction, and chemical specificity.

Ultra-High-Vacuum Surface Science

Recent effort in the area of UHV surface science has focused on the wide-bandgap semiconductors GaN and SiC and insulators ß-Si3N4 and ß-Ga2O3. The interest is in the physical and electronic structure of the surfaces, chemisorption phenomena, metal contact formation and functionalization with organic species.

Surface Infrared Spectroscopy

Infrared spectroscopy is being used to study the vibrational spectra of adsorbed species in vacuum, non-vacuum and liquid environments. The focus is on the study of surface reactions and on identifying both strongly-adsorbed stable species and also reaction intermediates and weakly-adsorbed moieties that are present only under steady-state conditions. The materials of interest are primarily semiconductors and dielectric materials in bulk, thin-film or nano-structure form. Experiments in vacuum or in the presence of gas-phase reagents use primarily reflection-absorption spectroscopy.

Quantum-Chemical Modeling of the Adsorption of Chemical Warfare Agents and Simulants

There is a critical need for a quantitative understanding of the interaction of chemical warfare agents (CWA's) with materials. Experimental work with real agents is extremely dangerous and, therefore, costly and time-consuming. Furthermore, because of the hazards involved, such work can be done only in a small number of specially-designed facilities. The goals are, first, to develop and test the necessary models. Secondly, the aim is to compare "side-by-side" the properties of simulants and real agents for the purpose of evaluating and improving the simulants. A third goal is a quantitative and microscopic understanding of how CWA's adsorb on prototypical oxides for the purpose of aiding in a "materials-by-design" approach to CWA detection, protection and remediation.

Stress driven model for the growth of Si NWs, in which the Si source is provided by the substrate due to enhanced diffusion Growth and Surface Properties of Semiconductor and Metal Oxide Nanowires

One-dimensional structures, such as carbon nanotubes and semiconductor nanowires, are currently of great interest due to their unique physical properties and potential applications, including nanoscale devices and sensors. We have been investigating a number of nanowire systems, from the perspective of growth mechanism, surface properties, as well as potential applications, especially to sensing.

Figure 1 Application of Dielectric/Metal Nanowire Composites to Surface Enhanced Raman Sensing

Optically based sensing provides advantages over electronic sensing because optical spectra can uniquely finger print a chemical compound, significantly reducing false alarms and simplifying the detection process. In Raman scattering (RS), light is scattered from a chemical of interest and the vibrational modes in the chemical red shift the frequency of the scattered light, producing a spectrum of lines that are characteristic of that molecule. The Raman signal can be enhanced by many orders of magnitude by the use of metal nano particles, referred to as surface enhanced Raman scattering (SERS).

Self-Assembly of Gold Nanocluster Devices

This project is a collaboration between researchers in NRL's Electronics S&T Division, Chemistry Division and Center for Biomolecular Science & Engineering. Ultra-small gold nanoclusters (2-3nm in diameter) could provide the foundation for new electronics/sensor technologies that are scalable to the few nanometer regime and would operate at room temperature. The main thrust of this project has been to develop fabrication methods suitable for assembling the nanoclusters into useful configurations.

Selected Publications

2012 Ancona, M., S. Binari, and D. J. Meyer, "Fully coupled thermoelectromechanical analysis of GaN high electron mobility transistor degradation", Journal of Applied Physics, vol. 111, issue 7, 2012. PDF icon 1.3698492.pdf (3 MB)
2011 Ancona, M., "Density-gradient theory: a macroscopic approach to quantum confinement and tunneling in semiconductor devices", Journal of Computational Electronics, vol. 10, issue 1-2, pp. 65-97, 2011. PDF icon 10-1226-2227.pdf (1.3 MB)
2010 Ancona, M., B. Bennett, and B. Boos John, "Scaling Projections for Sb-Based p-Channel FETs", Solid State Electronics, vol. 54, pp. 1349-1358, 11/2010. PDF icon 10-1226-0462.pdf (496.7 KB)