Sublimation growth of bulk AlN crystals: materials compatibility and crystal quality B.M. Epelbaum, D. Hofmann, M. Bickermann, A. Winnacker Department of Materials Science 6, University of Erlangen-Nürnberg, Martensstr. 7, 91058 Erlangen, Germany Keywords : AlN single crystal, bulk growth, sublimation growth, crucible material, AlN–SiC mixed crystals. Abstract. The main problem to be solved for stable growth of bulk pure AlN is the use of a suitable crucible material. Our analysis of the AlN sublimation growth process support the conclusion made by Slack and McNelly that tungsten is the best choice. However, in the real growth reactor tungsten must be combined with other materials to ensure flexible design and sufficient lifetime of the whole system. Compatibility of tungsten with other high-temperature structural and seed materials such as graphite, AlN and SiC is the topic of the present research. Introduction. Perspectives of bulk AlN crystal growth are attracting much interest, as AlN wafers would be a nearly ideal substrate for nitride based electronic and optoelectronic devices due to small lattice mismatch with GaN, similar coefficient of thermal expansion and high electrical resistivity. Since the pioneering work of Slack and McNelly [1] the problem of chemical compatibility of materials used in the growth cell was recognized as the key issue in bulk AlN growth. Various crucible materials such as graphite and SiC coated graphite, nitrides (TiN, Ta 2 N) and high-melting metals (W, Re, W–Re alloys) have been tested. However, AlN crystals grown are still limited in size and contain impurities (the latter is evidenced by crystal coloration). In this work, a systematic investigation of the compatibility of different materials in the reactor system was made and the results are discussed in terms of growth unit integrity, process stability and material quality. Experimental. Crystal growth experiments were conducted in a resistively heated furnace using graphite or tungsten heating elements in the temperature range of 1800–2200°C, see Fig. 1. The source material was commercially available AlN powder (99%, CHEMPUR, Germany), aluminum and oxygen in form of Al 2 O 3 being the main residual impurities. Seed plates of 10mm x 10mm were made of tungsten foil or cut from on axis 6H-SiC crystals grown in our laboratory. Growth was performed in an atmosphere of pure nitrogen and N 2 + H 2 /NH 3 mixtures with pressures in the range of 50–750 mbar. Material combinations listed in Table 1 were tested under different temperatures and the use of various ambient gas compositions. Table 1. Material combinations (arrangements) used in the model AlN reactor system N Crucible Heater Isolation 1 Dense graphite Graphite Porous graphite 1a Silicon carbide coating Graphite Porous graphite 2 2a Tungsten Tungsten Tungsten Tungsten Tungsten AlN ceramics 3 Tungsten Graphite Porous graphite