Stable Ohmic Contacts on GaAs and GaN Devices for High Temperatures
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L11.57.1
STABLE OHMIC CONTACTS ON GaAs AND GaN DEVICES FOR HIGH TEMPERATURES A. Piotrowska1 , E. Kaminska1 , A. Barcz1,2, K. Golaszewska1 , H. Wrzesinska1 , T. T. Piotrowski1 , E. Dynowska2 , R. Jakiela2 1 2
Institute of Electron Technology, Warsaw, Poland, Institute of Physics, PAS, Warsaw, Poland.
ABSTRACT We have studied thermal stability of Nb and NbN contacts to GaAs and GaN by x-ray diffraction and SIMS, and demonstrated their excellent behaviour under high temperature annealing. GaAs/Nb and GaAs/NbN contacts are stable up to 8000 C and 9000 C, respectively while GaN/NbN and GaN/Nb/NbN remain stable up to 10000 C. INTRODUCTION Device technology is usually driven by industrial and commercial requirements. This is particularly true in the field of high temperature and high power electronics, where applications range from communication links and electricity networks to high power domestic applications. Consequently, much of the work is concerned with fabrication of power rectifiers, HBTs and HEMTs based on GaAs and GaN, materials offering a high power handling capability. To ensure long-term device reliability in hot environments and power dissipation at a high output power, additional research is required to develop thermally stable metallization systems. Low melting point metallizations, commonly used for low resistivity ohmic contacts, readily react with semiconductor forming multiphase structures. Resultant grain boundaries and voids enhance inter-diffusion at the metal-semiconductor interface and initiate device degradation during operation at high temperatures. Amorphous thin films, free from grain boundaries and nucleation sites, have been shown to have many orders of magnitude lower diffusivities than their polycrystalline counter-partners. Refractory metals and their nitrides, offering an exceptional combination of properties like low resistivity, high melting point and resistance to corrosion [1] are considered as good materials for the development of thermally stable ohmic and gate contacts for high temperature GaAs- and GaN-based electronics. Until now the research effort has concentrated on nitrides and borides of Ti, Zr, Mo, Ta and W [2]. On the other hand, promising results have been obtained with single niobium and niobium nitride metallizations to GaAs and GaN [3-6]. Moreover, niobium being superconductor has attracted recently a big deal of attention for fabricating superconductor/semiconductor hybrid structures involving 2DEG in III-V semiconducting heterostructures [7, 8]. In this work we report on the applicability of thin films of Nb and NbN for thermally stable metallizations to GaAs and GaN. The effect of high temperature annealing on the microstructure of metal/semiconductor contact has been investigated using secondary ion mass spectrometry (SIMS) and x-ray diffraction (XRD) measurements. The electrical characterisation involved measurements of I-V characteristics for rectifying contacts and resistivity for ohmic contacts.
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EXPERIMENTAL DETAILS Bearing in mind typical devic
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