Metalorganic Chemical Deposition Research Articles

Raman scattering of ferroelectric lead lanthanum titanate thin films grown on fused quartz by metalorganic chemical vapor deposition

Highly textured lead lanthanum titanate (Pb 1− x La x )TiO 3 (PLT) thin films have been grown on fused quartz substrates by metalorganic chemical deposition (MOCVD). A series of PLT with different x between 0 and 0.32 were prepared and studied by Raman scattering. Raman spectra, measured at 300 K and 80 K, showed the features from the PLT film and quartz substrate. By using a “difference Raman” technique, more PLT modes are shown. The variations of the PLT Raman modes with the La composition and the measurement temperature are studied, and related physical phenomena and problems are discussed.

Electro-Optic and Magneto-Optic Photonic Bandgap Materials Kevin

ABSTRACTThis work presents a study of electro-optic and magneto-optic films made by a Metal-Organic Chemical Liquid Deposition (MOCLD) method. Electro-optic thin film, La-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PLMNT) and magneto-optic thin film, rare earth doped yittrium iron garnet (YIG) have been grown at different conditions. Low temperature growth on buffered semiconductor substrates has been studied for semiconductor device integration. High quality PLMNT film with EO coefficient of 1x10-16 (m/V)2 was obtained with MOCLD. Doped and undoped YIG onto MgO and glass substrates and also onto buffered semiconductors were successfully deposited using MOCLD method. Several of these films had successful rotations that were of device quality. Based on these high quality functional films, two dimensional photonic bandgap waveguide structures were designed and simulated.

Magnetic Relaxation and Flux Creep in Superconducting YBCO Thin Films

In this work, the temperature dependence of the magnetic relaxation in samples of YBa 2 Cu 3 O 7 (YBCO) thin films of two different qualities grown on MgO by metal organic chemical deposition technique (MOCVD) is measured in the range of 4.2–80 K using an initial applied magnetic field of 0.1 T. The relaxation data are analyzed in terms of a single effective activation energy and then more correctly of a distribution of activation energies. The single activation energies extracted are in broad agreement with published results.

Effects of TMIn flow rate of barrier layer on the optical and structural properties of In xGa 1− xN/In yGa 1− yN multiple quantum wells

We reported the effect of trimethylindium (TMIn) flow rate in the barrier layer on the structural and optical properties of In x Ga 1− x N/In y Ga 1− y N multiple quantum wells (MQWs) grown on (0001)-oriented sapphire substrates by low-pressure metalorganic chemical deposition (LP-MOCVD). It was found that the change of TMIn flow rate dramatically influences the interface quality and optical properties. Temperature-dependent photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) measurements provide proof evidence that the increment of TMIn flow rate deteriorates the interfacial abruptness, decreases the emission wavelength (blue shift) and the efficiency of nonradiative recombination process.

InGaN/GaN MQW high brightness LED grown by MOCVD

Abstract In this work, InGaN/GaN multi-quantum wells (MQWs) high brightness light emitting diode (LED) was grown by metalorganic chemical deposition (MOCVD). Photoluminescence (PL), X-ray diffraction (XRD), cathodoluminescence (CL), transmission electron microscope (TEM) were performed on the LED wafers to investigate the effects of growth temperature, well width and In composition in the InGaN quantum well on the emitting wavelength of LED. It was found that the wavelength of InGaN MQW-LED shifted from about 400–470 nm due to the difference in the In composition introducing into the InGaN well layer at different growth temperature. It was also demonstrated that the wavelength can be changed from 470 nm to 504 nm only by changed the thickness of the InGaN quantum well layer. Combined with the CL image and TEM observation, it was concluded that the change from MQW structure to multi-quantum dot structure would be the cause of the shift from 470 to 504 nm by changed the InGaN well width.

Ferroelectric Films and Multilayers with Ultrahigh Dielectric Constants

ABSTRACTThis work presents a systematic study of ferroelectric films and multilayers made by a metal-organic chemical liquid deposition method. BaxSr1-xTiO3, Pb(Mg1/3Nb2/3)O3-PbTiO3, and Pb(Zn1/3Nb2/3)O3-PbTiO3 films, as well as multilayers incorporated with these materials have been grown at different conditions. Ultrahigh dielectric constant (∼6700) has been achieved in the PMN/PZN-PT multilayers when the sublayer thickness approached to nanometer scale, where interfaces become dominant. When the sublayer materials with desired Curie temperatures were properly chosen, the temperature dependent dielectric constant of the multilayer structure could be greatly reduced. These nanostructured multilayers may find very important applications where temperature variation is a key concern. Pb doping in BaxSr1-xTiO3 was found very efficient in increasing the dielectric constant and reducing the loss. It is believed that the addition of Pb improved the film density and reduced the grain boundary defects.

Structural and electrical properties of polycrystalline PbZr 0.5 Ti 0.5 O 3 films deposited on La 0.5 Sr 0.5 CoO 3 coated silicon by sol-gel process

La0.5Sr0.5CoO3 (LSCO) films have been grown on Si (100) by a metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate, strontium acetate and cobalt acetate as the starting materials. Subsequent PbZr0.5Ti0.5O3 (PZT) films were deposited onto LSCO films by a modified sol-gel method. Field-emission scanning electron microscopy and X-ray diffraction analysis show that PZT and LSCO films are polycrystalline and entirely perovskite phase. At an applied electric field of 250 kV/cm, the Pt/PZT/LSCO capacitor shows no polarization fatigue after 3×109 switching cycles and an internal electric field; the remnant polarization Pr and the coercive field Ec are about 22 μC/cm2 and 73 kV/cm, respectively. The dielectric constant of PZT films is 650 at a frequency of 1 kHz.

Evaluation of Chemical Solution Deposited Ba x Sr 1−x TiO 3 Thin Films on LaAlO 3 in Tunable Microwave Devices

Epitaxial Ba x Sr 1 m x TiO 3 (BST) films grown on LaAlO 3 by several deposition methods have been tested in coupled microstrip phase shifters (CMPS) at frequencies from 10 to 24 GHz. To date the best performance for the devices has been achieved using Pulsed Laser Deposition (PLD). However, recently chemical solution deposition (CSD) methods such as sol-gel and Metal-Organic Chemical Liquid Deposition (MOCLD) have shown advances in fabricating BST films for tunable microwave applications. CSD processes promise improvements in cost, speed and area covered during BST film deposition. This paper compares over 35 BST films used in identical CMPS circuits. In this study, the highest measured figures of merit of phase shift per dB of loss for PLD, MOCLD and sol-gel CMPS are 49, 47 and 41°/dB respectively. While other phase shifter designs using BST films have surpassed these values, these data base of identical circuits allows us to compare the BST films. X-ray diffraction characterization for many of the BST films is also given.

Uniform Array of GaN Quantum Dots in AlGaN Matrix by Selective MOCVD Growth

We demonstrate GaN quantum dots (QDs) embedded in an AlGaN matrix, using metalorganic chemical vapor selective deposition, on a uniform array of hexagonal pyramids of GaN. The hexagonal pyramids have clear {1101} side facets and their radius of curvature at the tops is not larger than 10 nm, which indicates that very sharp tops are realized. Intense photoluminescence was observed from GaN QDs at a peak energy of 3.61 eV at room temperature.

State Filling in Type II Quantum Dots

Many-body states in self-organized type II GaSbAs/GaAs quantum dots grown by metal organic chemical vapor phase deposition are studied. With increasing exciton occupation the photoluminescence shows a blue shift and becomes significantly broader developing a saturated plateau structure. The results reveal the properties of many-hole states in GaSbAs quantum dots determined by Coulomb charging and state filling.

State Filling in Type II Quantum Dots

Many-body states in self-organized type II GaSbAs/GaAs quantum dots grown by metal organic chemical vapor phase deposition are studied. With increasing exciton occupation the photoluminescence shows a blue shift and becomes significantly broader developing a saturated plateau structure. The results reveal the properties of many-hole states in GaSbAs quantum dots determined by Coulomb charging and state filling.

Improvements of Structural and Optical Properties of GaN/Al0.10Ga0.9N Multi-Quantum Wells by Isoelectronic In-doping

Absratct:The effects of isoelectronic In-doping were studied on the structural and optical properties of 3-periods and 10-periods of GaN/Al0.10Ga0.90N multi quantum wells (MQWs). The GaN/Al40.10Ga0.90N MQWs were grown on u-GaN/sapphire via metalorganic chemical deposition (MOCVD) at 1050°C in H2 carrier gas. X-ray diffraction (XRD), and micro-Photoluminescence (PL) measurements revealed that In-doping into well layers improves the crystalline and optical properties of MQWs relative to those samples without In-doping. With increasing Trimethylindium (TMIn) flow rates from 4.2 mol/min to 42.6 mol/min, PL peaks from well layers obviously redshifted, due to the improvement of the strain along the interfaces between MQWS, irrespective of 3-periods or 10 periods MQWs. The improvement of the crystal quality was also confirmed by XRD.

A comparison of mocld with PLD BaxSr1−xTiO3 thin films on LaAIO3 for tunable microwave applications

Historically, tunable dielectric devices using thin crystalline BaxSr1-x TiO3 (BST) films deposited on lattice-matched substrates, such as LaAlO3, have generally been grown using pulsed laser deposition (PLD). Highly oriented BST films can be grown by PLD but large projects are hampered by constraints of deposition area, deposition time and expense. The Metal-Organic Chemical Liquid Deposition (MOCLD) process allows for larger areas, faster turnover and lower cost. Several BST films deposited on LaAlO3 by MOCLD have been tested in 16 GHz coupled microstrip phase shifters. They can be compared with many PLD BST films tested in the same circuit design. The MOCLD phase shifter performance of 293° phase shift with 53 V/μm dc bias and a figure of merit of 47°/dB is comparable to the most highly oriented PLD BST films. The PLD BST films used here have measured XRD full-width-at-half-maxima (FWHM) as low as 0.047°. The best FWHM of these MOCLD BST films has been measured to be 0.058°.

High quality BaxSr1-xTiO3 films grown by mocld and novel ferroelectric/ferrite structures for dual-tuning microwave devices

Excellent single crystal BaxSr1-xTiO3 (BST) films were grown on LaAlO3 substrates using the metal-organic chemical liquid deposition (MOCLD) method. Very low losses (tanδ ∽0.002-0.008) were measured from these films at 400 KHz. Biaxially oriented BST films were successfully grown on polycrystalline YIG substrates using both MOCLD and pulsed laser deposition methods with biaxially oriented MgO and YSZ buffer layers. The dielectric losses of the films range from 0.005 to 0.015 while 25% of dielectric constant change was observed with 40V bias voltage up to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range (77 K to 380 K). A dual-tuning microwave coplanar phase shifter using a BST film grown on a MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in GHz frequency range when an electric bias or a magnetic field was applied to the device.

Characterization of Pb(Zr0.53Ti0.47)O3 Films on GaN

GaN/Pb(Zr0.53Ti0.47)O3 structures have been fabricated by light radiation heating low-pressure metal-organic chemical deposition and pulsed laser deposition. These structures show leakage current lower than 10-11 A at applied voltage of 5 V. X-ray diffraction shows that ferroelectric Pb(Zr0.53Ti0.47)O3 films directly on GaN are well crystallized with perovskite structure. Because of the high thermal stability and relatively smaller mismatch between GaN and ferroelectrics in comparison with that of Si/ferroelectric structures, GaN looks like more promising as semiconductor active layer for metal-ferroelectric-semiconductor field effect transistors.

Luminescent studies of alloy Zn xCd 1− xSe quantum dots grown on ZnSe by metalorganic chemical vapor-phase deposition

Zn x Cd 1− x Se alloy quantum dots (QDs) with x in the range 0–0.39 are grown by metalorganic chemical vapor-phase deposition on ZnSe. Cathodoluminescence (CL) and photoluminescence (PL) were used to study these self-assembled quantum dots. CL imaging and spectra show that clusters of QDs are efficient luminescent sites. A large red shift of the low-temperature PL peak energy of QDs, despite an increase in Zn, is attributed to a considerable increase in their size. This increase in size is consistent with the results of recent theoretical models. In forming the self-assembled QDs, mismatch strain is regarded as the fundamental driving force. When the strain changes, through a change in the composition of Zn x Cd 1− x Se, QDs of a different size are obtained. A decrease in size, in turn, results in stronger quantum confinement effects. The size of the QDs is very sensitive to small changes of strain. Even a minute reduction in the zinc content of the QDs, achieved through a lengthening of growth interruptions, produces an observable blue shift of luminescence, as a result of the strengthening of the quantum confinement energy.

On the formation and nature of nanometer size clusters on the surface of ZnSe epilayers

ZnSe epilayers were grown on GaAs (001) substrates by metal organic chemical vapor phase deposition, using different group VI–II precursor flow ratios. Atomic force microscopy (AFM) examinations of their surface show that epilayers grown with a high VI/II ratio are not as stable as those grown with a low ratio. When exposed to air, Se clusters would appear and grow on the surface of the unstable epilayers. The ripening process could take as long as 50 days at room temperature. Secondary electron and cathodoluminescence images indicate that the clusters are more likely to emerge from areas of high defect density. Moreover, AFM topographic images of epilayers at an intermediate stage of ripening suggest that clusters near surface depressions would grow in size at the expense of others. By using a low accelerating voltage and allowing the clusters to grow to a size larger than the electron interaction volume, we used energy dispersive x-ray analysis to show that the clusters are made up entirely of Se.

Low Loss Ferroelectric Films Grown on Polycrystalline Ferrite Substrates for Dual-Tuning Microwave Devices

AbstractWe successfully deposited high quality biaxially oriented BaxSr1-xTiO3 thin films on polycrystalline yttrium iron garnet substrates using both the metal-organic chemical liquid deposition and pulsed laser deposition methods with biaxially oriented MgO and yttriumstabilized- zirconia buffer layers. The dielectric losses of the films range from 0.005 to 0.015 while 25% of dielectric constant change was observed with 40V bias voltage up to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range. A dual-tuning microwave phase shifter using a BST film grown on an MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in a wide frequency range when an electric bias or a magnetic field was applied to the device.

Depth-resolved cathodoluminescence study of ZnxCd1−xSe epilayer grown on (001) InP by metal organic chemical vapor phase deposition

Optical properties of zincblende structured ZnxCd1−xSe epilayer grown on InP by metal organic chemical vapor phase deposition at temperatures of 360, 400, and 440 °C are investigated with low temperature cathodoluminescence spectroscopy (CL). Both near band gap and deep level emissions are found for the samples grown at 400 °C and above, but deep level emissions are absent for the sample grown at 360 °C. We conclude that the growth temperature should be kept below the temperature at which InP begins to decompose and diffusion of III–V constituents into the epilayer occurs. Evidence of this diffusion comes from an analysis of depth resolved CL studies, which shows that the deep level emissions occur mainly at the epilayer/substrate interface. By monitoring the ratio of the intensity of the deep level emissions to that of the near band emissions, we find that this ratio is larger for samples grown at high temperatures than those at low temperatures. Indium diffusion from the substrate into the epilayer is most likely the source of these deep levels.

Fabrication of GaN epitaxial films on Al2O3/Si (001) substrates

Single crystal GaN films of hexagonal modification have been fabricated on Al2O3/Si (001) substrates via a low pressure metalorganic chemical deposition (LP-MOCVD) method. The full width at half-maximum of (0002) X-ray diffraction peak for the GaN film 1.1 mu m thick was 72 arcmin. and the mosaic structure of the film was the main cause of broadening to the X-ray diffraction peak. Al room temperature, the photoluminescence (PL) spectrum of GaN exhibited near band edge emission peaking at 365 nm.