| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Nanomaterials | Tuesday Sessions |
| Session NM-TuE |
| Session: | Nanofabrication and Nanodevices II |
| Presenter: | Anthony Boyd, US Naval Research Laboratory, USA |
| Authors: | A.K. Boyd, US Naval Research Laboratory, USA A. El Fatimy, Georgetown University, USA P. Barbara, Georgetown University, USA A. Nath, US Naval Research Laboratory, USA PM. Campbell, US Naval Research Laboratory, USA M. Currie, US Naval Research Laboratory, USA R.L. Myers-Ward, US Naval Research Laboratory, USA K.M. Daniels, US Naval Research Laboratory, USA D.K. Gaskill, US Naval Research Laboratory, USA |
| Correspondent: | Click to Email |
There is a clear need for fast, high efficiency, and broadband sensitive detectors. Graphene demonstrates great promise to fill this void, possessing high room temperature carrier mobility, up to 60000 cm2V-1s-1, and absorption of incoming radiation, ~2.3%. This absorption is impressive considering graphene is a single atomic layer thick. In the gigahertz (GHz) frequency range, the absorption is enhanced due to the Drude contribution of the free carriers. Synthesizing epitaxial graphene (EG) on SiC has the advantages of wafer scale size, low defect density, and being single crystal.[1] Growing high quality, conformal dielectric films with Atomic Layer Deposition (ALD) on EG is challenging due to the lack of dangling bonds which serve as nucleation sights for film growth. Researchers at this laboratory have developed a fluorine functionalization approach to overcome the challenge without negatively impacting graphene’s morphology and electronic properties to enable ALD of high-κ dielectrics onto EG for gated devices.[2]
We investigate two types of GHz detectors fabricated on EG. The first is an antenna coupled device. It utilizes two dissimilar contact metals, one for the source and the other for the drain, and the metal work function difference translates into asymmetric Seebeck voltages at each contact. We fabricated these devices with two types of EG: 1) a quasi-free standing bilayer graphene (QBLEG) and 2) a standard one monolayer EG (1ML). The second device is a field effect transistor constructed using 1ML EG with an asymmetric top gate that creates a PN junction and facilitates tuning the photovoltaic response . Both device types were fabricated using a lift off resist-based clean lithography process, have low contact resistance [3] and use metal work function asymmetry for detection, consistent with recent studies of the photothermoelectric effect mechanism.[4]
The devices were electrically characterized and then irradiated with a Backwards Wave Oscillator from 100 to 177GHz. The antenna coupled devices response varies with frequency, incident power, and demonstrates a distinct antenna coupling. The QBLEG shows a 3 to 4X increase in response over the standard 1ML. The response of the PN junctions depends on the radiation frequency and the gate voltage. At a fixed frequency, the device response can be doubled by tuning the gate voltage, consistent with the known dependence of the Seebeck coefficient with charge concentration.
[1] L. O. Nyakiti, et al MRS Bulletin 37, 1149 (2012)
[2] V. Wheeler et al Carbon 50, 2307 (2012)
[3] A. Nath, et al Applied Physics Letters 104, 224102 (2014)
[4] X. Cai, et al Nature Nanotechnology 9, 814 (2014)