Search

Abstract: In this paper, high-quality wurtzite indium nitride was epi-grown on sapphire substrates by plasma-assisted metal-organic molecule beam epitaxy system (PA-MOMBE). Structural and electrical properties of the InN films were significantly improved by employing a GaN buffer layer. In addition, high-resolution X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), Hall Effect, Raman and photoluminescence spectroscopy were carried out to characterize the effect of the growth temperature on structural and optoelectronic properties. It was found that highly c-axis oriented InN epilayer can be obtained by optimizing growth conditions. TEM images reveal that the epitaxially grown InN/GaN interface is sharp, and the spacing of the InN(0002) lattice plane is about 0.57nm. Raman spectra also show a sharp peak at 491cm−1 attributed to the E2(high) mode of wurtzite InN. These results indicate that the improvement of InN material quality can be achieved using heteroepitaxy on GaN/sapphire templates. [Copyright &y& Elsevier]

Abstract: We have investigated the effects of III/V ratio on the properties of InN films grown on sapphire substrates with oxide buffer by metalorganic molecular-beam epitaxy. The structural, optical and electrical properties of the InN films were investigated by X-ray diffraction, scanning electron microscopy, Hall-effect and temperature-dependent photoluminescence (PL) measurements. Near-infrared emission peaks between 0.74 and 0.78eV were observed. On increasing the III/V flux ratio, the PL emission peak red-shifted that is related to the reduction in carrier concentration. In addition, the PL spectra show an abnormal behavior with increase in temperature. The temperature-dependence PL spectra exhibit blue-shift as the temperature increased up to 150K and then red-shift, reflecting a competition between the blue-shift induced by thermal screening and the red-shift induced by electron–phonon interaction. [Copyright &y& Elsevier]

Abstract: Self-assembled high-density gallium nitride (GaN) nanorod arrays have been grown on (0001) Al2O3 substrates by metal-organic molecular beam epitaxy (MOMBE) using radio-frequency radical nitrogen. The corresponding microstructure and optical properties of nanorods were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), micro-Raman (μ-Raman) spectroscopy and temperature-dependent photoluminescence (PL). It was found that the length and diameter of nanorods varies with the growth temperatures, and the rod number density can reach around 1010 cm−2. HRTEM and corresponding diffraction patterns have revealed that the GaN nanorods have a dislocation-free, single-crystal hexagonal wurtzite structure. μ-Raman scattering reveals that the self-assembled nanorods are strain free in consistent with XRD and HRTEM results. In particular, the PL spectra show an abnormal behavior with increasing temperature. The so-called “S-shape” behavior, a red–blue–red shift of emission peak with increasing temperature, might result from the fluctuation in compositional contents or crystallographic defects. In contrast to previous works, the process requires neither catalyst nor the effect of nanometer-sized confinement such as carbon nanotubes. These strain-free GaN nanorods may find many important applications on the future development of optical nanodevices. [Copyright &y& Elsevier]

Abstract: The temperature dependence of optical properties of InGaAsN/GaAs single-quantum wells grown by solid source molecular beam epitaxy (MBE) with N contents varied from 0% to 5.3% was investigated by photoluminescence (PL). The evolution of the peak positions of InGaAs/GaAs sample are in agreement with the empirical Varshni model. However, pronounced temperature-dependent S-shaped peak positions and N-shaped linewidth were observed in PL spectra while increasing nitrogen concentration. The activation energy of InGaAsN/GaAs single quantum well (SQWs) is observed to decrease with nitrogen incorporation, which is contrary to the expectation of the bandgap reduction. This phenomenon suggests that the existence of defect-related nonradiative processes is due to nitrogen incorporation. The results of measurement demonstrate that the nitrogen incorporation into the InGaAsN has strong influence not only on carrier localization but also on the optical quality. In addition, the growth of high nitrogen content (5.3%) shows that the InGaAsN might be the potential candidate for long-wavelength optoelectronic devices. [Copyright &y& Elsevier]

Abstract: Transparent and conductive high-preferential c-axis-oriented Al-doped zinc oxide (ZnO:Al, AZO) thin films have been prepared by the sol–gel route. Film deposition was performed by spin-coating technique on Si(100) and glass substrate. Structural, electrical and optical properties were performed by XRD, SEM, four-point probe, photoluminescence (PL) and UV-VIS spectrum measurements. The effects of annealing temperature and dopant concentration on the structural and optical properties are well discussed. It was found that both annealing temperature and doping concentration alter the microstructures of AZO films. Also, PL spectra show two main peaks centered at about 380nm (UV) and 520nm (green). The variation of UV-to-green band emission was greatly influenced by annealing temperatures and doping concentration. Reduction in intensity ratio of UV-to-green might possibly originate from the formation of Al–O bonds and localized Al-impurity states. The minimum sheet resistance of 104 Ω/□ was obtained for the film doped with 1.6mol% Al, annealed at 750°C. Meanwhile, all AZO films deposited on glass are very transparent, between 80% and 95% transmittance, within the visible wavelength region. These results imply that the doping concentration did not have significant influence on transparent properties, but improve the electrical conductivity and diversify emission features. [Copyright &y& Elsevier]

Indium nitride (InN) films were deposited on Al 2 O 3 substrates with a zinc oxide (ZnO) interlayer using by radio-frequency metalorganic molecular beam epitaxy (RF-MOMBE). We evaluated the impact of the flow rate of trimethylindium (In(CH 3 ) 3 , TMIn) on the structure, surface morphology, and optical and electrical properties of the films using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, and Hall measurements. The XRD results indicated that all InN films were formed from single-phase wurtzite crystals with the preferred orientations along the c -axis. The SEM images indicated that the rough surfaces of the InN films grown with TMIn flow rates less than 0.55 sccm. The TEM images showed that InN and ZnO had hexagonal structures (wurtzite) that were epitaxially grown by RF-MOMBE on the substrates. The electron concentrations ranged from 7.3 × 10 19 to 2.56 × 10 20 cm −3 of the InN films were measured. [ABSTRACT FROM AUTHOR]

Abstract: This work reports on the heteroepitaxial growth of wurtzite indium nitride (InN) thin films on highly orientated n-ZnO buffer layer by RF metal-organic molecular beam epitaxy (RF-MOMBE) system. Highly orientated n-ZnO buffer layers were pre-sputtered using RF co-sputtering. We investigated the surface morphology and crystal structure properties by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), respectively. XRD pattern shows InN films were hexagonal wurtzite structure with preferential c-axis orientation. Electrical properties such as carrier concentration and mobility were performed by Hall measurement at room temperature. Particularly, the InN has high growth rate of 1.5μm/h. SEM images also reveal the InN surface become rough as increasing the flow rate of trimethylindium (TMI) vapor. Meanwhile, the carrier mobility decrease at higher TMI flow rate. The phenomena probably originate from surface imperfection by excess In incorporation in the films. These results indicate that the high-quality buffer layer is essential for engineering the growth of InN on silicon wafer, and it might be also applicable for other lattice-mismatched III–V heteroepitaxial systems. [Copyright &y& Elsevier]