AVS 63rd International Symposium & Exhibition
    2D Materials Focus Topic Friday Sessions
       Session 2D+NS-FrM

Paper 2D+NS-FrM5
Optical Detectors Based on Bismuth Telluride Nanowire Arrays Capped by Graphene

Friday, November 11, 2016, 9:40 am, Room 103B

Session: 2D Materials: Device Physics and Applications
Presenter: Tito Huber, Howard University
Authors: T. Huber, Howard University
T. Brower, Howard University
O. Abana, Howard University
Correspondent: Click to Email
Recently, research on graphene based photodetectors has drawn substantial attention. The gapless nature of graphene and low light absorption can cause low responsivity. The synergetic integration of graphene with other materials is a promising approach to overcome these shortcomings. There have been reports of broadband photodetectors based on heterostructructures of few-layer Bi(2)Te(3)/graphene devices that are very encouraging. Here we discuss a different approach, where single layer graphene caps the top of a bismuth telluride nanowire array (where the wire axis are perpendicular to the graphene surface) . Partially, our motivation was to test the exceptional thermoelectric properties of the interface. The room-temperature thermoelectric efficiencies of bismuth telluride compounds are the highest reported for any material, and, therefore, Bi(2)Te(3) nanowires are interesting as building blocks of nanoscale thermoelectric devices, as in this case. Graphene strong photothermoelectric response is also very well known. We employed devices composed of bismuth telluride nanowire arrays which are capped with single layer graphene. Dense arrays of 200-nm nanowires have been prepared by a nonlithographic fabrication technique consisting of the pressure injection of an alumina template with molten Bi2Te3, a method that can be successfully employed with 100-μm thick templates of pore diameters in the range of 2 to 200 nm. Bismuth telluride is a semiconductor with a small gap. The nanowire arrays electronic properties including magnetotransport and thermopower were characterized in separate experiments. The single layer graphene layer was fabricated by transfer by Graphenea. Graphene on the device was characterized using Raman spectroscopy. We observed the D, G and 2D peaks and broadening indicating that graphene is nearly intact. We also observed the Raman peaks of bismuth telluride. The incident surface features very low optical reflectivity and enhanced light trapping. Light trapping causes strong light absorption at the interface, an effect that counteracts the weak absorption of graphene and has not been mentioned in the literature before. The unique attributes of the thermoelectric arrays are the combination of strong temporal and optical wavelength dependences of the photocurrent. Under infrared illumination, the signal can be completely described by thermoelectric effects considering cooling rates given by heat diffusion through the array. We will discuss that, in addition, under visible illumination we observe a photovoltaic response. This work was supported by the National Science Foundation through PRDM 1205608 and STC 1231319