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 [1–7] and laser ablation [8–10] 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.
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