Effect of In/Al ratios on structural and optical properties of InAlN films grown on Si(100) by RF-MOMBE
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NANO EXPRESS
Open Access
Effect of In/Al ratios on structural and optical properties of InAlN films grown on Si(100) by RF-MOMBE Wei-Chun Chen1*, Yue-Han Wu2, Chun-Yen Peng2, Chien-Nan Hsiao1 and Li Chang2
Abstract InxAl1-xN films were deposited on Si(100) substrate using metal-organic molecular beam epitaxy. We investigated the effect of the trimethylindium/trimethylaluminum (TMIn/TMAl) flow ratios on the structural, morphological, and optical properties of InxAl1-xN films. Surface morphologies and microstructure of the InxAl1-xN films were measured by atomic force microscopy, scanning electron microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM), respectively. Optical properties of all films were evaluated using an ultraviolet/visible/infrared (UV/Vis/IR) reflection spectrophotometer. XRD and TEM results indicated that InxAl1-xN films were preferentially oriented in the c-axis direction. Besides, the growth rates of InxAl1-xN films were measured at around 0.6 μm/h in average. Reflection spectrum shows that the optical absorption of the InxAl1-xN films redshifts with an increase in the In composition. Keywords: InAlN; In/Al ratios; RF-MOMBE
Background Recently, InAlN film is a highly attractive III-nitride semiconductor with numerous potential applications because InAlN has band gap energy in the range from 6.2 eV for AlN to 0.7 eV for InN. Therefore, InAlN alloys are attractive for possible applications in light-emitting diode (LEDs) and high-efficiency multijunction tandem solar cell in the wide spectral range from ultraviolet to infrared [1-3]. In addition, compared with Ga(In, Al)N, InAlN has not been so intensively investigated because the growth of InAlN suffers from the difficulty of phase separation due to large immiscibility, optimum growth temperatures, lattice constant, bonding energy, and difference of thermal stability between InN and AlN [4]. Moreover, few studies have been performed because InAlN has an unstable region concerning miscibility [5]. Therefore, it was very difficult to grow high-quality InAlN since there were many variables in the growth condition.
* Correspondence: [email protected] 1 Instrument Technology Research Center, National Applied Research Laboratories, 20 R&D Rd. VI, Hsinchu Science Park, Hsinchu 30076, Taiwan Full list of author information is available at the end of the article
Previous studies of InAlN growth on an AlN buffer layer show that it has improved the crystallinity of the InAlN films and prevented oxygen diffusion from the substrate [6]. Besides, the growth of the InAlN film in all composition regions has been realized with the molecular beam epitaxy (MBE) growth method [7], while it was reported that In-rich InAlN with an In content >32% grown by metal-organic vapor phase epitaxy (MOVPE) showed the phase separation [8]. Also, Houchin et al. indicated that the film quality of InAlN was degraded with increasing Al content. However, phase separation is not observed for the films obtained in their study [9]. Kariya et al. conc
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