%0 Journal Article
%T Stress and Grain Boundary Properties of GaN Films Prepared by Pulsed Laser Deposition Technique
%A D. Ghosh
%A S. Hussain
%A B. Ghosh
%A R. Bhar
%A A. K. Pal
%J ISRN Materials Science
%D 2014
%R 10.1155/2014/521701
%X Polycrystalline gallium nitride films were successfully deposited on fused silica substrates by ablating a GaN target using pulsed Nd-YAG laser. Microstructural studies indicated an increase in the average crystallite size from ~8£¿nm to ~70£¿nm with the increase in substrate temperature from 300£¿K to 873£¿K during deposition. The films deposited here were nearly stoichiometric. XPS studies indicated two strong peaks located at ~1116.6£¿eV and ~395£¿eV for Ga2p3/2 and a N1s core-level peak, respectively. The films deposited at substrate temperature above 573£¿K are predominantly zinc blende in nature. PL spectra of the films deposited at higher temperatures were dominated by a strong peak at ~3.2£¿eV. FTIR spectra indicated a strong and broad absorption peak centered ~520£¿cm£¿1 with two shoulders at ~570£¿cm£¿1 and 584£¿cm£¿1. Characteristic Raman peak at ~531£¿cm£¿1 for the A1(TO) mode is observed for all the films. Grain boundary trap states varied between and £¿m£¿2, while barrier height at the grain boundaries varied between 12.4£¿meV and 37.14£¿meV. Stress in the films decreased with the increase in substrate temperature. 1. Introduction Gallium nitride (GaN) is a promising material for applications in optoelectronic devices, such as ultraviolet-blue-green light-emitting diodes (LEDs) and laser diodes (LDs), due to its direct wide band gap and good thermal stability. It is equally suitable for high-temperature and high-power electronic applications. Depending on the growth conditions, GaN crystallizes either in the stable hexagonal (wurtzite, -phase) or metastable cubic (zinc-blende, -phase) polytypes. The prevalent deposition techniques for depositing GaN thin films are mainly metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Recently, amorphous and polycrystalline GaN thin films deposited using magnetron sputtering technique [1¨C7] and laser ablation [8¨C10] technique have also been reported. GaN thin films with wurtzite structure were deposited by Chen et al. [5] by using reactive DC magnetron sputtering technique. The films exhibited a polycrystalline structure with a strong (002) orientation and were utilized as active channel layer to produce top-gate n-type thin-film transistors (TFTs). Highly textured polycrystalline GaN films having an average grain size of several hundred angstroms were obtained by Christie et al. [7] using an RF plasma-assisted molecular beam epitaxy system on quartz substrates. Zou et al. [6] reported the deposition of GaN films on glass substrates by the middle frequency magnetron sputtering method.
%U http://www.hindawi.com/journals/isrn.materials.science/2014/521701/