Solubility limits of dopants in 4H±SiC M.K. Linnarsson a,* , U. Zimmermann a , J. Wong-Leung b , A. Scho Èner c , M.S. Janson a , C. Jagadish b , B.G. Svensson a,d a Royal Institute of Technology, Solid State Electronics, P.O. Box E229, SE-164 40 Kista-Stockholm, Sweden b Department of Electronics Material Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia c ACREO AB, P.O. Box E236, SE-164 40 Kista-Stockholm, Sweden d Physical Electronics, Department of Physics, Oslo University, P.B. 1048 Blindern, N-0316 Oslo, Norway Abstract Epitaxial 4H±SiC structures with heavily boron or aluminium doped layers have been prepared by vapour phase epitaxy. The samples have been annealed in Ar atmosphere in an RF-heated furnace between 1700 and 2000 8Cfor45minto64h.Secondary ion mass spectrometry has been employed to obtain depth distributions as well as lateral distributions (ion imaging) for boron and aluminium. Transmission electron microscopy has been used to study the crystallinity and determine phase composition. Solubility limits of  1  10 20 Al/cm 3 (1700 8C) and < 1  10 20 B/cm 3 (1900 8C) have been deduced. # 2002 Elsevier Science B.V. All rights reserved. Keywords: SIMS; TEM; SiC; Solubility limit; Precipitates 1. Introduction Today, silicon carbide (SiC) of reasonable quality can be produced and during the last year a few semiconductor devices have reached the market. How- ever, in many applications the material quality is not good enough and a number of process problems remain to be solved. One key issue when realising SiC devices is to form high quality ohmic contacts. These layers can be prepared by ion implantation or during epitaxial growth taking advantage of site com- petition [1]. Dopant incorporation during epitaxial growth is kinetic-controlled and solubility limits may be exceeded. However, in subsequent annealing steps the thermodynamic equilibrium may be approached and phase separation can occur [2]. If the solubility limit is exceeded possible candidates for the precipitating species can be predicted from ternary phase diagrams [3±5]. Unfortunately, the area of interest for highly doped SiC is not known in detail. In this study, we report on solubility limits and precipitate formation in heavily boron and aluminium doped epitaxially grown p-type 4H±SiC. Secondary ion mass spectrometry (SIMS) has been utilised to obtain concentration versus depth pro®les as well as lateral distributions (ion images). These results have been further substantiated by transmission electron microscopy (TEM). 2. Experimental Epitaxial 4H±SiC structures with heavily boron or aluminium doped layers have been prepared by vapour Applied Surface Science 203±204 (2003) 427±432 * Corresponding author. Tel.: 46-8-752-14-12; fax: 46-8-752-77-82. E-mail address: marga@imit.kth.se (M.K. Linnarsson). 0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-4332(02)00694-3