Activity Report 2004-2008 (3,5 MB – 1st - IEMN

II.3-1 Wide Bandgap Devices for Microwave Power Amplification andDetectionPermanent Staff: J.C. De Jaeger, D. Ducatteau, C. Gaquiere, H. Gerard, B. Grimbert, V. Hoel,J. Lemaitre, M. Rousseau, A. Soltani, D. TheronNon Permanent Staff : H. Barkad, M. Benali, B. Benbakhti, S. Boulay, F. Carosella, A.Curutchet, N. Defrance, M. Elkhou, J.C. Gerbedoen, M. Mattalah, A. Minko, V. Raballand, X.Tang, S. Touati, N. Thouvenin, M. WerquinObjectivesThis task consists to develop devices based on wide bandgapsemiconductors mainly for microwave power applications. Itis based on physical simulation, technological processing,electrical and microwave measurement and powerperformance determination. During the last four years, theactivity was based on wide bandgap semiconductors such asgallium nitride and more innovative materials (BN anddiamond). The goal is the fabrication of power chips andpower amplifiers for military and telecommunicationapplications. A large part of the activity was developed inthe frame of TIGER, a common laboratory betweenTHALES III-V LAB and IEMN. It is a research field verycompetitive, studied since several years by the most famouslaboratories all around the world in USA, Europe and Japan.The second topic regards X-UV photodetectors for solarobservation missions.Outstanding results1) Physical-thermal simulationIn order to study the physical behaviour and thedetermination of the temperature in devices, a physicalthermalmodel was developed. This model is shared in twoparts: a 2D energy-balance physical model describing theelectrons transport in the active area of the device and athermal model determining the lattice temperature in thedevice (active area and substrate). It is based on theresolution of the heat equation.The model was used to simulate TLM structures in order toanalyze the saturation phenomenon of the current. It isshown that only the determination of the temperature in anypoint of the device, conditioning the dependence of theelectrons velocity according to this temperature, permits tounderstand the experimental observations. A goodagreement is observed between experimental I(V)characteristics and the temperature determination byMicro-Raman and the theoretical predictions. [B.Benbakhti et al, IEEE-ED, 53, (9), 2237-2242 (2006)].2) AlGaN/GaN HEMTsAlGaN/GaN HEMTs were fabricated and measured forpower applications. The activity is performed on epitaxiesgrown by MOCVD or MBE on different substrates such asSiC and Si(111) or advanced possibilities such as Si(001) orreported substrates. State of the art performance wasobtained for devices on Si(111) substrates at 18GHz with amicrowave power density of 5.1W/mm associated to a PAEof 18% and a power gain of 9dB (Fig.1). [D. Ducatteau etal, IEEE-EDL, 27, (9), 7-9 (2006)].Fig.1: Power performance of AlGaN/GaN device onSi(111) substrateIn order to increase the breakdown voltage, field plate (FP)transistors were studied. Two configurations are possible: aFP based on additional electrode (Fig.2) and a topologybased on a Γ shape.GFP300nm SiO 2/Si 3N 4Fig.2: Field plate transistorBoth topology optimizations were carried out by means of a2D-Energy-Balance model and permit to determine the bestcompromise between the breakdown behavior and themicrowave capabilities. At 10GHz, for a FP HEMT on SiCsubstrate a maximum output power density of 10.4W/mm isobtained with a PAE of 39% and a power gain of 13dB.The first results obtained from AlGaN/GaN HEMTs deviceson MBE and MOCVD epitaxial structures grown on“composite” substrates were obtained. These substrates arebased on innovative structures in which a thin top singlecrystal layer Si (SopSiC) or SiC (SiCopSiC) istransferred onto a thick polycrystalline SiC wafer with a thinSiO 2 intermediary insulating layer. The fabrication of theDActivity report 2004/2008 42