Pulsed Metalorganic Chemical Vapor Deposition Research Articles

Encapsulating the electroluminescent phosphor micro-particles using a pulsed metal-organic chemical vapor deposition process in a fluidized bed

The protective coating efficiency of illuminated phosphor micro-particles has been investigated. The coating was performed by a pulsed feeding metal-organic chemical vapor deposition (MOCVD) in a fluidized bed using aluminum tri-sec-butylate or aluminum isopropoxide as a precursor. This pulsed MOCVD process in a fluidized bed shows excellent performance for encapsulating micro-particles. The pulsed feeding and the fluidization minimize the agglomeration between the phosphor micro-particles during the MOCVD process. Coating thickness is also precisely controlled up to the range of a few angstroms in thickness. Furthermore, by feeding the explosive aluminum MO precursor separately with oxygen gas, the coating process has been performed more safely in the pulsed MOCVD process.

UV Emission Mechanisms in Quaternary AlInGaN Epilayers and Multiple Quantum Wells

AbstractWe present the results on investigation and analysis of photoluminescence (PL) dynamics of quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by a novel pulsed metalorganic chemical vapor deposition (PMOCVD). The emission peaks in both AlInGaN epilayers and MQWs show a blueshift with increasing excitation power density. The PL emission of quaternary samples is attributed to recombination of carriers/excitons localized at band-tail states. The PL decay time increases with decreasing emission photon energy, which is a characteristic of localized carrier/exciton recombination due to alloy disorder. The obtained properties of AlInGaN materials grown by a PMOCVD are similar to those of InGaN. This indicates that the AlInGaN system is promising for ultraviolet applications such as the InGaN system for blue light emitting diode and laser diode applications.

Metalorganic chemical vapor deposition of quaternary AlInGaN multiple quantum well structures for deep ultraviolet emitters

AbstractWe report on the growth of quaternary AlInGaN layers and MQWs by two different metalorganic chemical vapor deposition (MOCVD) techniques such as pulsed atomic layer epitaxy (PALE) and pulsed MOCVD (PMOCVD). For both growth processes, emission wavelength of quaternary MQWs can be tuned from 350 nm to 300 nm by simply changing the unit growth cell configurations. The PALE grown AlInGaN MQWs have a very smooth surface, few band tail states and exhibit a band-to-band emission. The PMOCVD grown AlInGaN MQWs exhibit a high density of band tail states, which strongly enhance spontaneous emission. Based on the characterization by photoluminescence, X-ray diffraction and AFM, both MOCVD techniques grown quaternary samples are shown to be promising for fabricating the active region of deep UV LEDs.

Characterization of Epitaxial Pb(Zrx,Ti1-x)O3 Thin Films with Composition Near the Morphotropic Phase Boundary

ABSTRACT200-nm-thick Pb(Zrx,Ti1-x)O3 (PZT) thin films with zirconium composition in the range from 0% to 65% were epitaxially grown on (001)c SrRuO3 (SRO)//SrTiO3 (STO) single crystal substrates by pulsed metalorganic chemical vapor deposition (pulsed MOCVD). Constituent crystallographic phases were characterized by high-resolution X-ray diffraction reciprocal space mapping. It was found that PZT thin films having zirconium composition from 45% to 60% show mixed tetragonal and pseudocubic phases and their lattice parameters remained constant in this composition range.

Special Issue Ceramics Integration. Change of Residual Stresses and Electrical Properties of Pb(Zr,Ti)O3 Thin Films Upon Introducing Various Bottom Electrodes.

Effects of Pb(Zr0.5Ti0.5)O3 (PZT) thickness on the residual stresses and the electrical properties of a PZT thin-film layer were discussed for the PZT/Pt/SrTiO3 or PZT/(La0.5Sr0.5)CoO3/SrTiO3 system. Bottom electrodes, i.e., Pt and (La, Sr)CoO3 (LSCO) thin films, were deposited by DC magnetron sputtering and pulsed laser deposition (PLD), respectively. PZT thin films with thicknesses of 30nm and 60nm were fabricated using the pulsed metal-organic chemical vapor deposition (MOCVD) apparatus. PZT films deposited on the LSCO electrodes were all epitaxially grown. The residual stress measurements by XRD revealed that all PZT films received the in-plane tensile stress from the substrate or the electrode/substrate. When the Pt and LSCO electrodes were introduced between the PZT film and the STO substrate, in-plane tensile stress in PZT was enhanced. With decreasing the PZT film thickness, the in-plane tensile stress in PZT film was enhanced. Remanent polarization decreased with increasing residual tensile stress in PZT film in all cases. The change of residual stress in the PZT/LSCO/STO system was discussed on the basis of the thermal expansion coefficient of the constituent layers.

Semiconductive Nb-doped BaTiO 3 films grown by pulsed injection metalorganic chemical vapor deposition

Semiconductive Nb-doped BaTiO 3 thin films were grown in situ by pulsed liquid-injection metalorganic chemical vapor deposition on (0 1 2) LaAlO 3 substrates. The films were epitaxially grown, althougth the quality decreased with increasing Nb content. The resistivity was strongly reduced after post-deposition annealing under argon. The room-temperature resistivity reached a minimum of 3 Ω cm for films with ∼2.4 at% Nb content (as measured by EDS). The semiconductive behavior was measured from room temperature up to 470 K and no positive temperature coefficient effect was observed.

Pulsed liquid-injection metalorganic chemical vapor deposition of (La0.7Sr0.3MnO3/SrTiO3)15 superlattices

( La 0.7 Sr 0.3 MnO 3 / SrTiO 3 ) 15 superlattices have been grown by pulsed liquid-injection metalorganic chemical vapor deposition on monocrystalline substrates such as LaAlO3, SrTiO3, and MgO. The pulsed-injection technique allows one to control precisely the amount of precursors delivered to the deposition chamber and thus the thickness of each individual layer. The period of the superlattices depends indeed linearly on the number of injected droplets. In our deposition conditions, the average growth rates are ∼0.130 nm/injection for La0.7Sr0.3MnO3 and 0.042 nm/injection for SrTiO3, with no significant difference as regard to the substrate used. The strain’s state of the superlattices depends on the relative thicknesses of the La0.7Sr0.3MnO3 and SrTiO3 layers and also on the substrate used. Finally, the deposition of superlattices with ultrathin interlayers of few unit cells has been demonstrated.

Epitaxial-grade polycrystalline Pb(Zr,Ti)O3 film deposited at low temperature by pulsed-metalorganic chemical vapor deposition

Epitaxial-grade polycrystalline Pb(Zr,Ti)O3 (PZT) films were deposited at 415 °C by source- gas-pulsed-introduced metalorganic chemical vapor deposition. The polycrystalline PZT film with Zr/(Zr+Ti)=0.35 which was prepared on (111)Pt/Ti/SiO2/Si substrate showed highly (100)- and (001)-preferred orientations. Well-saturated ferroelectricity with a remanent polarization (Pr) and coercive field of 41.4 μC/cm2 and 78.5 kV/cm, respectively, was obtained. This Pr value is almost the same as that of epitaxially grown films at 580 °C with the same composition and orientations taking into account of the volume fraction of (100) and (001) orientations.

Preparation of Pb(Zrx, Ti1-x)O3 Thin Films by Source Gas Pulse-Introduced Metalorganic Chemical Vapor Deposition

We prepared Pb(Zrx, Ti1-x)O3 [PZT] thin films on (111)Pt/Ti/SiO2/Si substrates at 620°C by metalorganic chemical vapor deposition (MOCVD). PZT [Zr/(Zr+Ti)=0.68] thin films of different thicknesses prepared by the conventional continuous source gas introduction MOCVD (continuous-MOCVD) and by pulsed gas introduction MOCVD (pulse-MOCVD) were compared to investigate the growth mechanism of these films. Stoichiometric PZT films were obtained for a wider range of Pb source input gas flow rates under fixed Zr and Ti sources for pulse-MOCVD compared with that for continuous-MOCVD. Highly (111)-oriented films were obtained for pulse-MOCVD regardless of their thickness, while the (111)-orientation decreased with film thickness for continuous-MOCVD. This suggests that the orientation homogeneity along the film thickness is higher for pulse-MOCVD films than for continuous-MOCVD films. The surface roughness of the pulse-MOCVD films was smaller than that of the continuous-MOCVD films and this result corresponds to the decrease of the leakage current density of the film. Well-saturated hysteresis loops with good square shapes were obtained, and the remanent polarization (Pr) and the coercive field (Ec) values of 100-nm-thick films prepared by pulse-MOCVD were 37 µC/cm2 and 82 kV/cm, respectively.

Vertically faceted lateral overgrowth of GaN on SiC with conducting buffer layers using pulsed metalorganic chemical vapor deposition

A “pulsed metalorganic chemical vapor deposition” technique has been developed for lateral overgrowth of GaN thin films on SiC with conducting buffer layers for vertically conducting devices. Growth was carried out at temperatures as low as 950 °C keeping a constant gallium flux while pulsing NH3. We demonstrate that, by varying the NH3 pulse duration, growth morphology can be gradually changed from triangular to rectangular for the lateral overgrowth. Even at a V/III ratio as low as 550, high quality smooth layers with (11̄00) vertical facets were successfully grown with a lateral to vertical growth rate ratio as high as 4:1. Atomic force microscopic measurements show the root-mean-square roughness of the laterally overgrown layers to be 7.0 Å. Scanning thermal microscopy was used to measure a thermal conductivity of 1.7 and 1.5 W/cm K, respectively, for the laterally overgrown film and the GaN deposition in the window region.

Low-temperature growth of Ti(C,N) thin films on D2 steel and Si(100) substrates by plasma-enhanced metalorganic chemical vapor deposition

We have deposited Ti(C,N) thin films on Si(100) and D2 steel substrates in the temperature range of 200–300 °C using tetrakis diethylamidotitanium (TDEAT) and titanium isopropoxide (TIP) by pulsed dc plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD). Radical formation and ionization behaviors in plasma are analyzed in situ by optical emission spectroscopy at various pulsed bias voltages and gas conditions. H2 and He+H2 gases are used as carrier gases to compare plasma parameters, and the effect of N2 and NH3 as reactive gas is also evaluated by the reduction of the C content of the films. Polycrystalline Ti(C,N) thin films were successfully grown on either D2 steel or Si(100) surfaces with TDEAT at temperatures as low as 200 °C. For TIP, however, only TiOCN thin films were obtained on Si(100) substrates. The best deposition process is evident for H2 and N2 gas atmospheres and bias voltage of 600 V. The higher film hardness is about 1760 Hk 0.01, but depends on gas species and bias voltage. Compared to TiN films, the Ti(C,N) film grown by PEMOCVD has very good conformability; the step coverage exceeds 85%, with an aspect ratio of more than 3.

High quality YBa 2Cu 3O 7 films grown on LaAlO 3 by single source pulsed metalorganic chemical vapor deposition

The possibilities of a new single source injection metalorganic chemical vapor deposition technique were demonstrated for in situ growth of YBa 2Cu 3O 7 films of very high crystalline and transport quality. Precisely controlled microamounts of organometallic β-diketonates dissolved in an organic solvent were injected sequentially into the evaporator by means of a computer-driven injector and the resultant vapor was transported into the deposition zone. Accuracy of microdosing (within 5%) and nonselective flash-like evaporation of the precursors were the main factors for obtaining a reproducible vapor phase composition in spite of poor stability of the Ba precursor. The influence of vapor phase composition on film properties was investigated. After the optimisation of deposition conditions, the YBa 2Cu 3O 7 films with very high critical current density up to (6–7)×10 6 A/cm 2 at 77 K were reproducibly grown on LaAlO 3(0 0 1).

In situ characterization of a plasma metalorganic chemical vapour deposition process

A 40 kHz pulsed plasma metalorganic chemical vapour deposition process using tetrakis (diethylamido) titanium as precursor was investigated by means of in situ methods. Mass and energy distributions were measured separately for ions and neutral particles utilizing a two-stage differentially pumped mass spectrometer equipped with an energy analyser. Using ammonia as an additional nitrogen source, the reduction in C x H + y ion flux and the dominance of NH + x ions correlate with a reduction in carbon incorporation in the Ti-C-N layers. The texture of the fine-grained films deposited at 150°C depends on the energy of incident ions. The measured ion energy distributions, different to some extent for different ionic species, give reason to assume that most of the ions detected are generated in the cathode layer.

Epitaxial LiTaO3 thin film by pulsed metalorganic chemical vapor deposition from a single precursor

Epitaxial LiTaO3 thin films were grown on (0001) sapphire in a low pressure chemical vapor deposition reactor of a new design, using lithium tantalum hexa-t-butoxide as the precursor. X-ray diffraction shows that the LiTaO3 c axis is normal to the sapphire surface. The x-ray pole figure and cross-section transmission electron microscopy diffraction show that the films were also in-plane oriented, with sapphire [101̄0] parallel to lithium tantalate [101̄0]. The refractive index of the film compares well with bulk values, over a wide wavelength range.

Advances in high Tc superconducting thin film research at srl-istec

Thin film research at SRL is focussed on in two major area: 1. (1) understanding the mechanisms of film growth of oxide superconductors, and 2. (2) developing superconducting oxide films with correct chemical composition and perfect crystal structure. The oxide films are being fabricated by evaporation, pulsed laser ablation, rf sputtering, and metalorganic chemical vapor deposition. Key features of these systems include oxidation using O + beams, in-situ monitoring of film surface structure by reflection high energy election diffraction (RHEED), in-situ examining of chemical composition by total-reflection-angle X-ray spectroscopy (TRAXS), and analysis of ablated species using time of flight mass spectroscopy.