RBS/Channeling study of Er doped GaN ®lms grown by MBE on Si111 substrates K. Lorenz a , R. Vianden a , R. Birkhahn b , A.J. Steckl b , M.F. da Silva c,d , J.C. Soares c,d , E. Alves c,d, * a ISKP, University of Bonn, Bonn, Germany b University of Cincinnati, Nanoelectronics Lab, Cincinnati, OH, USA c Department F  õsica, Instituto Technologico e Nuclear, Estrada Nac. 10, 2685-953, Sacavem, Portugal d CFNUL, Av. Prof. Gama Pinto 2, 1699 Lisboa, Portugal Abstract The in¯uence of the Ga cell temperature on the quality of GaN ®lms grown by MBE on p-Si(1 1 1) substrates was studied for cell temperatures (T Ga ) in the range from 865°C to 922°C using the RBS/Channeling technique. The ®lms were in situ doped during growth with Er at a constant cell temperature. The ®lms show a strong dependence of the crystalline quality on the Ga cell temperature with the best ®lms grown at T Ga  915  C. For temperatures T Ga below 880°C the ®lms showed no channeling eect. The thickness increases linearly with the temperature suggesting that changes in the Ga ¯ux in¯uence the growth process. The decrease of the Ga ¯ux allows the incorporation of higher Er concentrations in the ®lms. The data showed that a maximum value of about 0.35 at% was reached under the chosen growth conditions. The Er ions occupy mainly the Ga sublattice in the ®lms with single crystalline quality. A com- parison of the angular scans through the á0001ñ and the á10  11ñ axes with Monte Carlo simulations leads to the conclusion that a majority (90%) of the Er ions occupies Ga sites. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 81.05Ea; 81.15Hi; 81.70Jb Keywords: GaN epilayers; Er doping; Lattice location 1. Introduction The move from development of the wide band- gap semiconducting materials into the production of commercially available optical devices in the blue wavelength range has a signi®cant technological interest. The new group III-nitride compounds be- long to this class of materials and reveal a great potential for applications namely as LEDs and la- sers working in the blue region [1,2]. During the last decade, mainly GaN and to a lesser extent AlN and InN have been subject to an intensive research eort in order to improve their structural quality using dierent combinations of techniques and sub- strates. Despite of the work done, the structural and chemical dierences between the materials com- monly used as substrates (e.g. a-Al 2 O 3 , Si and Nuclear Instruments and Methods in Physics Research B 161±163 (2000) 946±951 www.elsevier.nl/locate/nimb * Corresponding author. Tel: +351-21-994-6000; fax: +351- 21-994-1525. E-mail address: ealves@itn1.itn.pt (E. Alves). 0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 6 8 3 - 7