Journal of Crystal Growth 221 (2000) 293}296 Structural investigation of GaN layers grown on Si(1 1 1) substrates using a nitridated AlAs bu!er layer A. Strittmatter*, D. Bimberg, A. Krost, J. Bla K sing, P. Veit Technische Universita ( t Berlin, Institut fu ( r Festko ( rperphysik, Sekr. PN 5-2, Hardenbergstr. 36, 10623 Berlin, Germany Otto-von-Guericke-Universita ( t, Institut fu ( r Experimentelle Physik, PF 4120, 38109 Magdeburg, Germany Abstract GaN layers are grown by metalorganic chemical vapor deposition (MOCVD) on Si(1 1 1) substrates. X-ray di!raction (XRD) measurements and cross-section transmission electron microscopy (TEM) show a comparable crystalline quality of the samples to the quality of GaN/sapphire samples. Both the characteristic symmetric GaN(0 0 0 2) and the asymmetric GaN(1 0! 1 5) X-ray re#ections have full-widths at half-maximum of 600}700 arcsec. The dislocation density as estimated from TEM investigation is found to be of the order of 10 cm. The initially deposited AlAs nucleation layer is transformed into AlN by supplying ammonia to the AlAs layer. This bu!er layer can be completely etched o! thus providing an easy way for substrate-layer separation after growth, an essential step for avoiding absorption of radiation emitted from nitride layers in the silicon substrate.  2000 Elsevier Science B.V. All rights reserved. PACS: 68.55.Jk; 78.55.Cr; 78.66.Fd Keywords: MOCVD; GaN; Si(111) substrates; TEM; AFM; PL Silicon substrates are of great interest as low- cost, large-area substrates for the growth of III}V nitride layers. A number of companies attempted to adopt growth processes for InGaN-based light emitting diode (LED) structures, which are well- established on sapphire substrates, for the growth on silicon substrates [1}4]. Although these LED structures electrically operate at room temperature, their performance is inferior to sapphire-based LED structures. It is argued that the higher defect density in GaN layers grown on Si-substrates as compared to GaN layers on sapphire substrates * Corresponding author. Tel.: #49-30-314-22060; fax: #49- 30-314-22569. E-mail address: strittma@sol.physik.tu-berlin.de (A. Stritt- matter). decreases the doping e$ciency for p-type doping [3]. As demonstrated earlier, the use of an AlAs/AlN bu!er layer leads to GaN layers on silicon substrates with comparable quality to GaN/sapphire samples [5]. Here, we present a detailed analysis of the structure of the AlAs/AlN bu!er layer and the GaN layer. The GaN layers are grown by MOCVD using an Aixtron 200 machine equipped with an additional AsH  -line and an infrared lamp heater specially designed by us. Si(1 1 1) substrates are used and a wet-chemical preparation is applied prior to growth to obtain an oxide-free and hydrogen- terminated surface. The epitaxy is started by the deposition of an AlAs nucleation layer at 4503C followed by an AlAs layer grown at 7203C which is grown to obtain a smooth surface. Afterwards, this 0022-0248/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 7 0 2 - 8