Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors q E. Danielsson a, * , C.-M. Zetterling a , M. Domeij a , M. € Ostling a , U. Forsberg b , E. Janz en b a KTH, Department of Microelectronics and Information Technology, P.O. Box Electrum 229, S-164 40 Kista, Sweden b Department of Physics and Measurement Technology, Link€ oping University, S-581 83 Link€ oping, Sweden Received 15 January 2002; received in revised form 27 February 2002; accepted 16 April 2002 Abstract Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 °C,usingtheassumptionthatthecurrentgainonlydependsontemperature.Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increaseinthevicinityofthedevice.Thedevicewasalsotestedinaswitchedsetup,showingfastturnonandturnoffat 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivityisfittedagainsttheself-heating,andthelifetimeinthebaseisfittedagainstthemeasurementofthecurrent gain. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Bipolar transistor; Thermal conductivity; Breakdown voltage 1. Introduction Silicon carbide (SiC) is a material used for high power and high temperature devices, and superior per- formance is expected compared to similar devices in silicon. Previous research on switching devices has been focused mainly on field effect devices (e.g. MOSFET, MESFET, and JFET) due to their voltage control and unipolar properties. In contrast, only a few publications have been presented on SiC bipolar junction transistors (BJT) [1–4]. One of the main reasons for this is the short minority carrier lifetime in p-type layers, which is det- rimental to the current gain. However, as the material quality improves and epilayer growth develops, SiC bi- polar transistors will be very competitive. As a switch the bipolar transistor has the advantages of carrier modulation and high current capabilities compared to most FETs. In thyristors and IGBTs, the main current flow has a pn-barrier to cross, resulting in an initial forward voltage-drop almost equal to the built in volt- age(3 V for 4H-SiC). In comparison, the BJT has two n-regions beneath the contacts in its main current path, which results in a lower initial voltage drop over the switch [5]. Some of the drawbacks of high voltage bi- polar transistors in silicon are the Kirk effect and sec- ondary breakdown, which occur already at moderate current densities. The SiC BJT has almost two orders of magnitude higher doping density for a similar voltage rating, resulting in a much higher critical current density q This paper was part of the ‘‘International Semiconductor Device Research Symposium ISDRS 2001 Special Issue’’ this paper should have been published in Volume 47, Issue 2. The publishers apologise for any inconvenience caused. * Corresponding author. Tel.: +46-8-752-1253; fax: +46-8- 752-7850. E-mail address: erikd@ele.kth.se (E. Danielsson). 0038-1101/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0038-1101(02)00218-6 Solid-State Electronics 47 (2003) 639–644 www.elsevier.com/locate/sse