Materials Science and Engineering B50 (1997) 228 – 232 Growth of columnar aluminum nitride layers on Si(111) by molecular beam epitaxy S. Karmann, H.P.D. Schenk, U. Kaiser, A. Fissel, Wo. Richter * Friedrich -Schiller -Uniersita ¨t Jena, Institut fu ¨r Festko ¨rperphysik, Max -Wien -Platz 1, D-07743 Jena, Germany Abstract Single crystalline aluminum nitride (AlN) thin films are deposited by molecular beam epitaxy (MBE) using thermally evaporated aluminum and RF-plasma excited nitrogen gas. In this paper we report on films grown on Si(111) at substrate temperatures of 800° with growth rates between 65 and 350 nm h -1 . All layers consist of hexagonal and exactly c -axis oriented AlN crystals with column-like structure. For the smoothest layers surface roughness (rms) around 1 nm is obtained. In the XRD-spectra ( -scan) we have achieved a minimum FWHM of 0.4° ( =25) for the AlN(00.2) reflex. At maximum growth rates (350 nm h -1 ) for AlN a transition zone of about 200 nm is formed with high defect density compared to the subsequent growth. For lower growth rates (65 nm h -1 ) no transition zone exists. Application of a substrate nitridation leads to a partial loss of epitaxial relation between AlN layer and Si(111)-substrate. © 1997 Elsevier Science S.A. Keywords: AlN; Film; Si(111)-substrate; MBE; TEM 1. Introduction Aluminum nitride (AlN) is a promising material for application in electro-acoustic, acousto-optical and op- toelectronic devices. It is a dielectric and refractory material which may act as insulating, passivating or cladding layer. AlN based ternaries (M x Al 1 -x N with M =Ga, In) might play a role as well in light emitting devices as LEDs and laser diodes. AlN is applied as buffer layer for the growth of GaN on sapphire (Al 2 O 3 ) substrates [1,2]. Due to its compatibility with GaN and its good thermal and lattice match to  -SiC, AlN has begun to play a role in GaN growth on 6H-SiC(0001) nowadays [3 – 5]. Growth of AlN on Al 2 O 3 (0001), Si(100), Si(111) and 6H-SiC(0001) has been thoroughly investigated by sev- eral groups using different deposition techniques as summarized in Table 1. The table also shows results from structural analysis of the layers (FWHM of XRD- peaks) and their surface roughness (R rms , mostly mea- sured by AFM). MOCVD generally tends to yield the better layer quality compared to the other techniques and the use of Si(111) substrates seems to be superior to Si(100). Volmer – Weber (island) growth resulting in a highly c -axis oriented column-like morphology and a mosaic surface texture appears to be a typical feature of most of the AlN layers fabricated so far. Typical di- ameters of the column-like structures on Si(111) be- tween 10 and 100 nm are reported. The resulting surface roughness is R rms 1 nm for the smoothest reported layers. These values are comparable with our own results presented in this work. Only recently Tanaka et al. [3] reported pseudomor- phically strained growth on 6H-SiC(0001) for an AlN film of 1.5 nm thickness. 2. Experimental details The AlN film deposition is performed in an ultra high vacuum chamber (base pressure 10 -9 mbar) using pure aluminum and nitrogen as source materials. Acti- vated nitrogen is supplied by a commercial RF-plasma source (Oxford MPD 21). A forward power of 300 W and a gas flow in the order of some sccm are typical parameters for the reported growth process. The UHV system is evacuated by a turbo molecular pump (speed 1.500 l s -1 for nitrogen). The total pressure during AlN deposition ranges in the lower 10 -5 mbar region. The * Corresponding author. Tel.: +49 3641 947440; fax: +49 3641 947442; e-mail: richter@pinet.uni-jena.de 0921-5107/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S09 21- 5 1 07(97)00 1 68 -2