InfraredandRaman-scatteringstudiesin single-crystallineGaNnanowires Hsiang-LinLiu a, * ,Chia-ChunChen b ,Chih-TaChia a ,Chun-ChiaYeh b , Chun-HoChen b ,Ming-YuanYu b ,StaciaKeller c ,StevenP.DenBaars c a Department of Physics, National Taiwan Normal University, 88, Sec. 4, Ting-Chou Road, Taipei 116, Taiwan b Department of Chemistry, National Taiwan Normal University, 88, Sec. 4, Ting-Chou Road, Taipei 116, Taiwan c Department of Electrical and Computer Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106, USA Received16May2001 Abstract Infrared and Raman-scattering studies of high-purity and -quality GaN nanowires are presented. The nanosize dependencesofthepeakshiftandthebroadeningofthefour®rst-orderRamanmodesagreewiththosecalculatedon the basis of the phonon con®nement model. Additionally, the appearance of one Raman mode at 254cm 1 isat- tributed to zone-boundary phonon activated by surface disorders and ®nite-size eects. Moreover, the Raman-scat- teringintensitiesofcertainphononsshowadierentresonantlyenhancedbehavior,whichcanbeusedtoverifythe information on the electronic structures and the electron±phonon interaction in GaN nanowires. Ó 2001 Elsevier ScienceB.V.Allrightsreserved. 1. Introduction The wide-band-gap semiconductor GaN is currentlyofgreatinterestfordevelopmentofop- toelectronic devices at blue and near-ultraviolet wavelengthsaswellashigh-temperatureandhigh- frequency electronics. There has been particular interest recently in the one-dimensional 1-D) nanostructures based on GaN compound [1±4]. These 1-D semiconductor nanostructures nano- wires) are electronic con®ned systems ideal for fundamental studies of their physical properties and for the fabrications of new optoelectronic nanodevices.Recently,wehavedevelopedalarge- scale synthesis of GaN nanowires from the cata- lytic reaction of gallium and ammonium using various metals as a catalyst [3]. Subsequently, breakthrough have been made to achieve high- purity and -quality synthesis of the GaN nano- wiresbycarefuloptimizingthegrowthconditions [4]. Inspiteofremarkableprogressinthegrowthof the GaN nanowires, information on their funda- mental physical properties still remain poorly studied. Knowledge of the lattice dynamics and the electron±phonon interaction is therefore very importanttounderstandtheopticalandelectronic properties of devices based on such structures. BothinfraredandRamanspectroscopyhavebeen proved to be the eective tools for probing the phononic and electronic excitations in semicon- ductor nanostructures [5±7]. In this Letter, we 14September2001 ChemicalPhysicsLetters3452001)245±251 www.elsevier.com/locate/cplett * Correspondingauthor.Fax:+886-2-29326408. E-mail address: hliu@phy03.phy.ntnu.edu.twH.-L.Liu). 0009-2614/01/$-seefrontmatter Ó 2001ElsevierScienceB.V.Allrightsreserved. PII:S0009-261401)00858-2