Eur. Phys. J. Appl. Phys. 30, 77–82 (2005) DOI: 10.1051/epjap:2005025 T HE EUROPEAN P HYSICAL JOURNAL APPLIED PHYSICS Temperature measurement in AlGaN/GaN High-Electron-Mobility Transistors using micro-Raman scattering spectroscopy R. Aubry 1, a , C. Dua 1 , J.-C. Jacquet 1 , F. Lemaire 1 , P. Galtier 1 , B. Dessertenne 1 , Y. Cordier 2 , M.-A. DiForte-Poisson 1 , and S.L. Delage 1 1 Thales Research and Technology, Domaine de Corbeville, 91404 Orsay Cedex, France 2 CRHEA-CNRS, rue Bernard Gregory, 06560 Valbonne, France Received: 19 June 2003 / Received in final form: 28 July 2004 / Accepted: 21 December 2004 Published online: 11 March 2005 – c  EDP Sciences Abstract. High power RF device performance decreases as operation temperature increases (e.g. decreas- ing electron mobility affects cut-off frequencies and degrades device reliability). Therefore determination of device temperature is a key issue for device topology optimisation. In this work the temperature varia- tion of AlGaN/GaN high-electron-mobility transistors grown either on silicon or sapphire substrate under bias operation was measured by micro Raman scattering spectroscopy. Temperature measurements up to power dissipation of 16 W for 4 mm development devices were carried out and a peak temperature of 650 K was determined. The difference of thermal resistance for similar devices grown on the two different substrates was assessed. The thermal resistances of different device topologies were compared to optimise the component design. PACS. 78.20.Nv Thermooptical and photothermal effects – 78.30.Fs III-V and II-VI semiconductors – 84.40.Dc Microwave circuits 1 Introduction GaN and its related alloys constitute a family of wide bandgap semiconductors suitable for optoelectronics and power microwave applications. For the latter applications, their high breakdown fields in the 3 MV/cm range and their high peak electron velocity of 2.7 × 10 7 cm/s are crucial. The high electron mobility transistor (HEMT) on GaN is very suitable for high frequency and power appli- cations. Moreover, these materials show excellent chem- ical and metallurgical stability. Excellent high frequency (f t = 110 GHz for a 0.15 μm gate length [1]) and high power density (10.7 W/mm at 10 GHz [2]) behaviour were demonstrated by different laboratories. As a result of these properties, the component can withstand high junction temperatures up to 500 K and above. However those high temperatures are known to reduce the de- vice electrical efficiency, due to the thermal dependence of the electron mobility [3,4]. Good power management is an important issue in order to achieve a higher out- put in GaN HEMTs. It is very important to understand the thermal conduction in the devices and this experiment is based on direct measurement of the local temperature distribution. Recently, laboratories reported the tempera- ture measurement of an active device by Raman scattering a e-mail: raphael.aubry@thalesgroup.com spectroscopy. One peculiarity of GaN stems from the fact that the crystal growth is mostly achieved on heteroge- neous substrates, which are not lattice matched, due to the lack of commercial GaN substrates. The substrates currently chosen are sapphire, silicon carbide and recently silicon. These substrates show very different thermal con- ductivity at 300 K since λ Sapphire = 50 W.m -1 .K -1 , λ SiC = 450 W.m -1 .K -1 and λ Si = 150 W.m -1 .K -1 (300 K), while λ GaN = 130 W.m -1 .K -1 . In this work, we measured the temperature distri- bution in AlGaN/GaN HEMTs on sapphire and silicon substrates by micro Raman scattering spectroscopy. The experiment was performed on two-finger HEMT grown on the two different substrates to determine the im- pact of substrate on the junction temperature. We also performed these measurements on different multi-finger HEMT grown on silicon to analyse the effect of the devel- opment. The measures were made at different bias points to determine the thermal resistance of the devices. Materials: Two AlGaN/GaN HEMT epitaxial lay- ers were processed. The first Al 0.3 Ga 0.7 N/GaN struc- ture was grown on Si by gas source molecular beam epitaxy using NH 3 as a nitrogen precursor, as well as Ga and Al elemental sources. The structure was: 1 nm GaN/30 nm Al 0.3 Ga 0.7 N/1.5 μm GaN (nid)/520 nm AlN/280 μm Si(111). The Hall effect measurements across