The Formation and Characterization of Epitaxial Titanium Carbide Contacts to 4H-SiC
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The Formation and Characterization of Epitaxial Titanium Carbide Contacts to 4H-SiC S.-K. Lee1, E. Danielsson1, C.-M. Zetterling1, M. Östling1, J.-P. Palmquist2, H. Högberg2 and U. Jansson2 1 KTH, Royal Institute of Technology, Dept. of Electronics, S-164 40, Kista, SWEDEN 2 Uppsala University, Dept. of Inorganic Chemistry, S-751 21, Uppsala, SWEDEN
ABSTRACT Epitaxial TiC Ohmic and Schottky contacts to 4H-SiC were formed by a new deposition method, UHV co-evaporation with Ti and C60, at low temperature (< 500oC). We achieved a contact resistivity of 2 × 10-5 Ωcm2 at 25oC for as deposited Ohmic contacts on Al ion implanted 4H-Silicon carbide. The rectifying behavior of TiC Schottky contacts was also investigated using I-V and C-V. The measured Schottky barrier height (SBH) was 1.26 eV for n-type and 1.65 eV for p-type 4H-SiC using C-V measurements for frequencies ranging from 1kHz to 1MHz. LEED, RBS, XPS, and XRD measurements were performed to analyze composition ratio, interface reaction, and structural properties of the TiC epitaxial layer.
INTRODUCTION Silicon carbide (SiC) devices are presently being developed for high temperature and high power applications under which conventional semiconductors hardly can perform. Metalsemiconductor Schottky contacts to silicon carbide have useful device application including metal-semiconductor field-effect transistor (MESFETs) and fast-switching rectifiers [1]. An important technological problem currently limiting device performance in some instances is the fabrication of high temperature stable Schottky contacts and low resistivity Ohmic contacts. For silicon carbide, many research reports have been published on electrical contacts, both Schottky and Ohmic. Lower specific contact resistance is usually obtained to n-type 4H- and 6H-SiC (∼10-4 to 10-6 Ω⋅cm-2) than to p-type 4H- and 6H-SiC (∼10-3 to 10-5 Ω⋅cm-2) [2, 3]. Generally, lowering the barrier height or increasing the doping concentration can reduce contact resistance [4]. Regardless of the higher doping, high temperature (> 700oC) thermal annealing was used to obtain the minimum possible Ohmic contact resistivities. This high temperature annealing process causes interface reaction which is undesirable for thin metal layers to SiC devices, restricts device fabrication, and makes contact morphology rougher. Ion implantation is one of the alternative solutions to increase the amount donors and acceptors for formation of low resistivity Ohmic contacts. The attention for ion implantation is increasing in SiC process technology due to the various advantages even with difficulties such as a high sheet resistivity and low activation efficiency [5]. The contact material should be selected for low-resistivity, reaction properties and compatibility to the process for SiC device application. Viewed in this light, titanium carbide (TiC) is a potentially interesting metal for both Ohmic and Schottky contacts. It has quite low resistivity and is very inert with respect to reaction with SiC under high temperature. In this paper we
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