LO phonon–plasmon coupling and mechanical disorder-induced effect in the Raman spectra of GaAsN alloys T. Tite a , O. Pag es a, * , M. Ajjoun a , J.P. Laurenti a , D. Bormann b , E. Tourni  e c , O. Maksimov d , M.C. Tamargo d a Institut de Physique, Universite de Metz, 1 Bd. Arago, 57078 Metz, France b Laboratoire de Physico-Chimie des Interfaces et Applications, Rue Souvraz, 62037 Lens, France c Centre de Recherche sur l’H et ero epitaxie et ses Applications, Rue Gregory, 06560 Valbonne, France d City College of New York, New York 10031, USA Abstract Mechanical and chemical disorders are investigated in GaAsN alloys with N content close to the solubility limit, 2– 3 %. One attractive characteristic, yet unexplored, of N-based III–V ternary alloys is that they consist in mixed crystals with a sharp contrast in the bulk modulus of the two constituents. Raman scattering is well-suited for its investigation because it addresses the force constant of the bond, which depends on the mechanical properties of the host matrix. In the Ga–N region, we observe a mode at 425 cm 1 , i.e. below the local mode of N in GaAs at 470 cm 1 . This mode has degenerated LO and TO components and seems to grow at fixed frequency with N content. From a direct comparison with Zn–Be chalcogenides, which exhibit a similar mechanical contrast, it is attributed to GaN vibrations in hard-like N-rich bounded regions, dispersed within the soft-like Ga-rich matrix. In the GaAs region we use Si-doping as a sensitive probe to investigate the structural quality close to the solubility limit. At low N content (n P 10 18 cm 3 ), we observe similar LO phonon–plasmon (LOP) coupling as in GaAs:Si. Unexpectedly LOP coupling is disorder-cancelled at higher N contents while the pure LO and disorder-activated theoretically forbidden TO modes substitute for it. Disorder-induced red-side LO asymmetries are fairly accounted for by the spatial correlation model with Gaussian distribution and the fitted value of correlation length is a quantitative indication for the disorder rate. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: GaAsN; Disorder; Raman spectroscopy; Hard/soft modes; LO phonon–plasmon coupling 1. Introduction The GaAsN semiconductor alloys with 2–4% N concentration attract considerable attention since the strong band gap reduction upon N incorporation [1] together with the use of GaAs as a substrate allow the realization of optical telecommunication devices [2] as well as high-efficiency solar cells [3]. However, among the III–V ternary alloys investi- gated up to now, GaAsN is the first one which consists in mixed crystals with a sharp contrast in the bulk modulus of the two binary constituents [4]: 0.756 and 2.054 Mbar for GaAs and GaN, respectively. Therefore, beside the usual chemical disorders (structural and/or topological) the appearance of a new type of disorder, namely mechanical disorder, can be feared, even at moderate N incorporations. Indeed, this has quite been observed recently by Raman scattering (RS) spectros- copy in Zn–Be chalcogenides [5,6] which exhibit a sim- ilar mechanical contrast although shear––instead of bulk-modulus is then involved. Above the percolation * Corresponding author. Tel.: +33-3-87-31-58-73; fax: +33-3- 87-31-58-01. E-mail address: pages@sciences.univ-metz.fr (O. Pag es). 0038-1101/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0038-1101(02)00388-X Solid-State Electronics 47 (2003) 455–460 www.elsevier.com/locate/sse