Microstructure and Thermal Stability of Transition Metal Nitrides and Borides on GaN
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Microstructure and Thermal Stability of Transition Metal Nitrides and Borides on GaN , Anna Piotrowska3, Adam Barcz3,40DUFLQ=LHOL 1 Lawrence Berkeley National Laboratory, Materials Science Division, Berkeley, CA 2 Institute of Experimental Physics, Warsaw University, Hoza 69, Warsaw, Poland 3 Institute of Electron Technology, Al. Lotnikow 46, Warsaw, Poland 4 Institute of Physics, PAS, Al. Lotnikow 46, Warsaw, Poland -DFHN-DVL
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ABSTRACT Microstructure and thermal stability of ZrN/ZrB2 bilayer deposited on GaN have been studied using transmission electron microscopy methods (TEM) and secondary ion mass spectrometry (SIMS). It has been demonstrated that annealing of the contact structure at 11000C in N2 atmosphere does not lead to any observable metal/ semiconductor interaction. In contrast, a failure of the integrity of ZrN/ZrB2 metallization at 8000C, when the heat treatment is performed in O2 ambient has been observed. INTRODUCTION One of the most challenging problems in the fabrication of GaN-based devices is the development of thermally stable metallization. This is especially important because material properties of GaN make it the most suitable, from among other III-V compound semiconductors, for high-temperature and high-power electronics. The subject of reliable metallization for GaN is extensively studied, and there have been reports on the thermal stability of a variety of metal/GaN contacts. However, in most of these studies pure metal contacts such as Al, W, Ni, Pd, and Pt with stability limited to 7000C have been used [1-5]. On the other hand, the majority of thermally stable contacts systems, implemented with Si and GaAs-based devices rely on refractory transition metal nitrides and borides. These materials are distinguished for their exceptional combination of properties like low resistivity, high melting point, hardness and resistance to corrosion. Such characteristics might also be essential in preventing the decomposition of GaN during thermal processing steps such as formation of ohmic contacts or post-implantation annealing. We have previously reported an approach for improving the reliability of metallization to n-GaN by using TiN diffusion barrier [6]. Excellent stability of TiN in contact to GaN up to annealing temperature of 9000C has been demonstrated. In the present study, in search for metallization systems with further improved resistance to high-temperature treatment we investigate ZrN/ZrB2 bilayers. The presence of nitrogen in the film adjacent to GaN is a key factor in preventing the decomposition of the semiconductor. Taking into account recent reports concerning the impact of annealing ambient on electrical properties of metal/GaN contacts [7], we compare the microstructure and thermal stability of contacts heat treated in both nitrogen and oxygen atmosphere.
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EXPERIMENTAL PROCEDURE GaN epilayers grown via organometallic vapor phase epitaxy on sapphire have been used in this study. Zr-based layers, nominally 100 nm thick, were pre
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