III-nitride nanostructures for optical gas detection and pH sensing Sumit Paul a , Konrad Maier a , Aparna Das c , Florian Furtmayr b , Andreas Helwig* a , Jörg Teubert b , Eva Monroy c , Gerhard Müller a and Martin Eickhoff b a EADS Innovation Works, 81663 Munich, Germany, b I. Physikalisches Institut, Justus-Liebig- Universität Gießen , 35392 Gießen, Germany, c NAC,SP2M,NPSC, CEA-Grenoble, 38054 Grenoble ABSTRACT The paper presents a novel concept for the realization of optochemical sensor systems which are capable of operating in harsh environments. Key components in such sensors are nanostructures formed from gallium nitride (GaN) and its alloys with aluminum (Al) and indium (In). Nanostructures of this kind emit an efficient, visible-light photoluminescence (PL) which can be excited with low-cost ultraviolet light sources and which extends up to temperatures in the order of 200°C. When exposed to various chemical environments, changes in the PL intensity occur which constitute valuable sensor signals. Due to the all-optical approach, the PL can be excited and its chemically- induced changes be read out without requiring electrical wiring at the point of measurement. The present paper presents this innovative sensor concept, the nanostructures and optochemical transducer structures that form its material base, as well as several applications of such transducers in the fields of gas and fluid sensing. The applications addressed here range from the sensing of ppb concentrations of H 2 , NO 2 and O 3 in gaseous environments to the pH monitoring in aqueous solutions. Keywords: III-nitride semiconductors, nanowires, nano-heterostructures, quantum dots, photoluminescence, gas sensor, fluid sensor 1. INTRODUCTION III-nitride materials such as GaN and its alloys with Al and In have received an increasing attention during the past two decades 1 . During this time, GaN-based wide-bandgap semiconductors have rapidly developed into a reliable technology base for the realization of high-temperature, high-frequency and optoelectronic devices 2 . In particular, GaN-based alloys form the material base for a rapidly developing solid state lighting technology 3 . In addition to these mainstream applications, GaN-based semiconductors have also received increasing attention in the field of chemical and bio- chemical sensors 4,5,6,7,8,9,10,11 . So far most of this work has used the superior transport characteristics of GaN-based high electron mobility transistors (HEMTs) to arrive at high-quality chemo-resistive transducers. Employing devices with very thin noble metal coatings, hydrogen and hydrocarbon sensors could be obtained 12 . Uncoated devices with a presumably oxidized GaN surface have produced NO 2 gas sensors with single ppb sensitivities 13 . While most of the work on III-nitride-based chemical sensors has used fairly conventional chemical-to-electrical transducer principles, well known from research on other material systems, very little work has yet been reported which makes a consistent use of the excellent optoelectronic properties of the III-nitride material system. The present work aims into this direction, describing innovative research that had been performed in the European Union funded project “DOTSENSE”. This project had been devoted to the development of III-nitride based optochemical nano-transducers and to developing and demonstrating sensor applications based on such nano-transducers. *Andreas.Helwig@eads.net; phone +49(0)89 607 28197; fax +49(0)89 607 24001; www.eads.com Invited Paper Micro- and Nanotechnology Sensors, Systems, and Applications V, edited by Thomas George, M. Saif Islam, Achyut K. Dutta, Proc. of SPIE Vol. 8725, 87250K · © 2013 SPIE CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2015221 Proc. of SPIE Vol. 8725 87250K-1