Al-Oxynitride Buffer Layer Facilities for PrO X /SiC Interfaces
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0996-H05-23
Al-Oxynitride Buffer Layer Facilities for PrOX/SiC Interfaces Karsten Henkel, Rakesh Sohal, Carola Schwiertz, Yevgen Burkov, Mohamed Torche, and Dieter Schmeißer Angewandte Physik-Sensorik, BTU Cottbus, K.-Wachsmann-Allee 17, Cottbus, 03046, Germany
ABSTRACT We investigate the dielectric properties of Praseodymium based oxides and silicates by preparing MIS structures consisting of a metal layer (M), PrOX (praseodymium oxide) as a highk insulating layer (I), and silicon (Si) or silicon carbide (SiC) as semiconductor substrates (S). The use of a buffer layer between PrOX and SiC is necessary as we found destructive interactions like silicate and graphite formation between these materials. Based on a higher permittivity value than SiO2 and a good lattice matching in conjunction with nearly the same thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. We report on results achieved by Synchrotron Radiation Photoemission Spectroscopy (SRPES) and by electrical measurements. In our spectroscopic investigations we found a stable AlON/3C-SiC interface as well as no elemental carbon and silicate contributions in the core levels after thin PrOX deposition and annealing up to 900°C. In electrical characterizations of PrOX/AlON stacks on silicon we already found a strong improvement in the leakage current down to values of 10-7 A/cm2 at an CET of 4nm. We observed an interface state density in the range of 5x1011-1x1012/eVcm2 and 1-5x1012/eVcm2 on Si and SiC, respectively. INTRODUCTION Materials like Silicon carbide and Gallium nitride are favorable for high frequency, high power and high temperature applications [1]. For the use in high electrical fields high bandgaps are necessary; however, in a MIS-like structure the insulator material has to withstand even high electrical fields, as the electrical field strength is scaling by Gaussian law at the interface. Therefore, the use of a high-k material may reduce the field strength in the insulator. Pr2O3 is one of the promising high-k oxides [2], permittivity values up to 30 have been reported [3]. In this paper we will focus on the need of insertion of a buffer layer between the insulator and the semiconductor in our system. Generally, it is difficult to deposit thermally PrOX directly on the surface of the investigated semiconductors, as we found destructive interactions like graphite formation on SiC [4] and silicate formation on silicon [5]. This fact might strongly influence the properties of the interface and we observed poor electrical performance of such MIS stacks [6]. Furthermore, high-k materials tend to decreased values of the bandgap by increasing their k-values [7], leading to lower band offsets [8]. So on the one hand, the buffer layer should hinder charge injection from the semiconductor into the insulator. On the other hand, it should prevent outdiffusions from the semiconductor into the insulator resulting in unintentionally interfacial layer formation. In referen
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