Novel Sensor Applications of group-III nitrides
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Novel Sensor Applications of group-III nitrides M. Eickhoff, O. Ambacher, G. Steinhoff, J. Schalwig1, R. Neuberger1, T. Palacios2, E. Monroy2, F. Calle, G. Müller1 and M. Stutzmann Walter Schottky Institute, Technical University Munich, Am Coulombwall, D-85748 Garching, Germany 1 EADS Deutschland AG, IRT/LG-MX, P.O. Box 800465, D-81663 Munich, Germany 2 ISOM and Dpto. de Ingeneria Electronica, ETSI Telecomunicación, Univ. Politécnica de Madrid, 28040 Madrid, Spain
ABSTRACT The present paper gives an overview over different sensor applications of GaN thin films and AlGaN/GaN heterostructures. The response of Pt-GaN Schottky diodes towards hydrogen and hydrogen containing gases is analysed and their gas sensitivity is characterized from room temperature up to 600°C. In addition, the sheet carrier density of a two dimensional electron gas confined at the heterointerface in AlGaN/GaN high electron mobility transistors (HEMTs) is shown to be significantly influenced by changes in the electronic properties of the device surface. This effect is successfully exploited for the realization of ion detectors and sensors for fluid monitoring based on AlGaN/GaN HEMTs with non-metalized gate areas. Promising possibilities of fabricating monolithically integrated sensor devices for wireless signal transmission are demonstrated by the realization of SAW devices on epitaxial AlN-films.
INTRODUCTION In addition to their high temperature and high frequency capability in electronic devices, wide bandgap semiconductors like silicon carbide, diamond or III-nitrides exhibit material properties which make them promising materials for sensor applications in harsh environment. In the case of III-nitrides, which due to their band gap variability are up to now mainly considered for optoelectronic applications [1], recent experiments have shown their capabilities in solar blind UV-detectors [2] and piezoresistive sensors for dynamic pressure sensing [3,4]. The present work gives an overview over the main experimental observations concerning other sensor applications of GaN layers and HEMT devices based on undoped AlGaN/GaN heterostructures as well as first attempts to understand and exploit the physics behind those phenomena for optimization of the sensor response. In the second paragraph gas sensitive devices based on PtGaN Schottky diodes are described. These sensors are shown to respond to hydrogen and various hydrogen containing gases like hydrocarbons. Similar devices have been realized before using other semiconductor materials, for example Si-MOS structures with catalytic Pd-gates [5] or SiC-MOS structures with Pt-gates [6]. Due to the spontaneous and, in the case of pseudomorphic growth, piezoelectric polarization of III-nitrides, a polarization induced two dimensional electron gas (2DEG) is formed at the heterointerface of AlGaN/GaN heterostructures. The corresponding sheet carrier density turns out to be highly sensitive towards any manipulation of the electronic state of the device surface, which is described in the third paragraph.
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