Physica B 308–310 (2001) 730–733 Deep level defects in sublimation-grown 6H silicon carbide investigated by DLTS and EPR K. Irmscher a, *, I. Pintilie b , L. Pintilie b , D. Schulz a a Institut f . ur Kristallz . uchtung, Max-Born-Str. 2, D-12489 Berlin, Germany b National Institute of Materials Physics, Bucharest-Magurele, P.O. Box MG-7, R-76900, Romania Abstract 6H-SiC bulk single crystals grown by physical vapor transport (PVT) were investigated by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). One of the observed deep level defects was identified as isolated tungsten on Si sites by EPR. The electron spin of 1 2 could be explained by W 5+ (5d 1 ). This is equivalent to the single positive charge state of a double donor when taking into account the Fermi level position in the n-type samples. The interpretation is also consistent with the DLTS detection of a W related deep level which showed a behavior of the capture of electrons and holes that hints at a double donor. In addition a tantalum related deep level is tentatively discussed. W and Ta were incorporated on electrically active sites in 6H-SiC only in low concentrations (2–4  10 14 cm 3 ) during crystal growth by PVT. r 2001 Elsevier Science B.V. All rights reserved. PACS: 61.72.Ss; 71.55.Ht; 78.30.He Keywords: 6H-SiC; DLTS; EPR; Tungsten; Tantalum 1. Introduction The high temperatures during the PVT growth of 6H- SiC crystals bear the risk of unintentional impurity incorporation and incomplete annihilation of intrinsic point defects. Many of these impurities and defects form deep levels which can alter the electrical properties of the crystal by their action as compensation or recombina- tion centers. Therefore, we investigated our 6H-SiC PVT crystals by DLTS and EPR to find out which deep levels are present, their concentration and electrical para- meters as well as their structural and chemical identity. Especially, we were interested if tungsten and tantalum, which are potential impurities in our crystal growth process, were incorporated as deep level defects. Recent investigations of W and Ta implanted SiC by radiotracer DLTS revealed deep levels which could unambiguously assigned to W and Ta related defects, respectively [1,2]. However, such experiments cannot prove whether the chemically identified impurity is incorporated on a substitutional or an interstitial site, and if it is isolated or associated with other defects. We report about the EPR identification of W substitut- ing for Si in 6H-SiC and its assignation to a deep double donor level for the first time. A tentative correlation of the measurements in the case of Ta is also given. 2. Experimental details 6H-SiC bulk single crystals 30 mm in diameter were grown by physical vapor transport using 6H(0 0 0 1)-SiC seeds with about 31 off-orientation. The sublimation of the SiC source took place at about 22001C in an inductively heated crucible made of graphite [3]. For the most investigated crystal of this report 5 wt% of metallic tantalum was added to the source powder without deterioration of the resulting crystal quality. Further- more, this crystal was only unintentionally doped with nitrogen and we obtained n-type samples in the mid 10 16 cm 3 range. *Corresponding author. Tel.: +49-30-6392-3090; fax: +49- 30-6392-3003. E-mail address: irmscher@ikz-berlin.de (K. Irmscher). 0921-4526/01/$-see front matter r 2001 Elsevier Science B.V. All rights reserved. PII:S0921-4526(01)00887-0