Graphene field effect transistor as a radiation and photo detector Ozhan Koybasi a , Isaac Childres a , Igor Jovanovic b ,Yong P. Chen* a,c a Dept. of Physics, Purdue University, West Lafayette, IN 47907 b Dept. of Mechanical and Nuclear Engineering, Penn State University, University Park, PA, 16802 c Birck Nanotechnology Center and School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907 ABSTRACT We exploit the dependence of the electrical conductivity of graphene on a local electric field, which can be abruptly changed by charge carriers generated by ionizing radiation in an absorber material, to develop novel high- performance radiation sensors for detection of photons and other kinds of ionizing radiation. This new detection concept is implemented by configuring graphene as a field effect transistor (FET) on a radiation-absorbing undoped semiconductor substrate and applying a gate voltage across the sensor to drift charge carriers created by incident photons to the neighborhood of graphene, which gives rise to local electric field perturbations that change graphene resistance. Promising results have been obtained with CVD graphene FETs fabricated on various semiconductor substrates that have different bandgaps and stopping powers to address different application regimes. In particular, graphene FETs made on SiC have exhibited a ~200% increase in graphene resistance at a gate voltage of 50 V when exposed to room light at room temperature. Systematic studies have proven that the observed response is a field effect. Keywords: graphene, transistor, radiation detector, photodetector, field effect 1. INTRODUCTION Graphene [1] has become a focus of rigorous research both in academia and industry due to its many exceptional properties and potential in device applications such as sensors and transistors. The sensitivity of electrical properties of graphene to local electric field changes [2] has led to the idea that graphene configured into a field effect transistor (FET) can be utilized to detect light photons and other types of ionizing radiation, potentially with improved capabilities compared to more conventional radiation detectors, such as high sensitivity and resolution, low electronic noise, low power, and operation at room temperature. The charge carriers induced in the absorber substrate by the incident photons can modify the electric field in the vicinity of graphene, causing a change in the graphene resistivity. The device structure, detection concept and measurement schematics have been presented previously by us and c-workers [3-8] and are depicted in Figure 1. Our prototype graphene FET sensor is made of a graphene layer on an electrically gated undoped radiation absorber substrate with an optional insulating layer in between. A gate voltage, V G , is applied across the sensor to generate electric field which is varied to find the optimum point on the Dirac curve for a sharp change in graphene resistance. Invited Paper Micro- and Nanotechnology Sensors, Systems, and Applications IV, edited by Thomas George, M. Saif Islam, Achyut Dutta, Proc. of SPIE Vol. 8373, 83730H © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.919628 Proc. of SPIE Vol. 8373 83730H-1 Downloaded from SPIE Digital Library on 15 Jun 2012 to 128.210.68.204. Terms of Use: http://spiedl.org/terms