Friday Morning Sessions (June 28) TMS Logo

About the 1996 Electronic Materials Conference: Friday Morning Sessions (June 28)

June 26-28, 1996 · 38TH ELECTRONIC MATERIALS CONFERENCE · Santa Barbara, California

Session X: Electronic/Photonic Oxides

Session Chairman: J. Raynien Kwo, AT&T Bell Labs, 600 Mountain Avenue, Rm. 1D232, Murray Hill, NJ 07974. Co Chairman: Bruce Wessels, Northwestern University, Department of Materials Science and Engineering, 2225 N. Campus Dr., Evanston, IL 60208

8:20AM, X1+

"Er-Doped Epitaxial BaTiO3 Thin Films and Their Optical Properties:" B.A. BLOCK, D. Gill, S.T. Ho, B.W. Wessels, Dept. of Materials Sci. & Eng. and Materials Research Center, Department of Electrical Engineering and Computer Science and Materials Research Center, Northwestern University, Evanston, IL 60208

Er doped BaTiO3 is an attractive candidate for a non-linear, high gain optical medium. In order to fabricate high gain miniature waveguide amplifiers and lasers for integrated optical applications, high concentrations of optically active rare earth ions must be incorporated into the waveguide host, while limiting the detrimental effects of concentration quenching or other non-radiativeloss mechanisms. We have previously shown that high concentrations of Er on the order of 1021 cm-3can be incorporated into BaTiO3 epitaxial thin films synthesized by metal-organic chemical vapor deposition. Strong characteristic Er3+ luminescence was observed at 1.54 um at room temperature. Although no concentration quenching was noted, a significant non-radiative component to the excited state decay of the Er3+ ion was present and manifested itself as non-exponential, accelerated decay in the transient decay measurements. In this study, we investigated improving the efficiency of the desired optical transition at 1.54 um, by optimizing growth conditions. We observed that a reduced growth temperature of less than 750deg.C resulted in materials with improved emission properties. The measured luminescence decay curves were single exponential with a 7 ms lifetime, consistent with highly efficient radiative decay. It is presumed that at lower growth temperatures, the defect center responsible for the non-radiative relaxation is not formed.

To attain high optical gain, optical scattering losses must be minimized especially from surfaces. The surface roughness of the epitaxial layers was investigated as a function of growth temperature and rate. Under optimal growth conditions, the surface roughness was as low as 3 nm for a 0.2 um thick layer, as determined by atomic force microscopy. Ridge waveguide structures have been fabricated using epitaxial films deposited on MgO by standard lithographic techniques. Light from a HeNe laser has been successfully coupled into the guides by end-firing and guiding was observed. The optical properties of the waveguides will be reported.

8:40AM, X2+

"Metal Organic Chemical Vapor Deposition of ß-BaB2O4:" DANIEL STUDEBAKER, Tobin Marks, George Wong, Thomas H. Baum, Advanced Technology Materials, Inc., 7 Commerce Dr., Danbury, CT 06810; Northwestern University, Department of Chemistry, 2145 Sheridan Rd., Evanston, IL 60208; Northwestern University, Department of Physics, 2145 Sheridan Rd., Evanston, IL 60208

Tunable lasers are desired to produce radiation at many different wavelengths. Currently lasers cannot produce radiation in the ultra-violet region of the spectrum. In order to produce laser radiation in the UV, a non- linear optical crystal such as [[beta]]-BaB2O4(BBO) can be used to generate higher harmonics of the laser.

Bulk crystalline [[beta]]-BaB2O4 has been grown by a top- seeded technique from a high temperature flux. There is an increasing interest in producing thin films of BBO on low refractive index substrates for waveguiding applications. [[beta]]-BaB2O4 thin films have been grown by liquid delivery metal- organic chemical vapor deposition onto platinum, fused silica, and silicon. to the best of our knowledge, this is the first reported example of the growth of BBO by MOCVD.

Liquid delivery CVD has been extremely useful for the controlled delivery of Group II metal organics and for the formation of complex metal oxide films. One example, is the CVD of Ba(1 x)SrxTiO3 thin films, in which the reproducible control of each constituent and the deposited film's stoichiometry is critical. Using this same technology, BBO films for non-linear optical applications have been grown through a controlled process.

This talk will focus on the effects of substrate identity, vaporizer conditions, precursor chemistry and the resultant quality or properties of the deposited films. the non-linear optical qualities of the thin films will also be discussed.

9:00AM, X3

"Thermal, Oxidative and Hydrolytic Decomposition of Precursors for the MOCVD of Barium Strontium Titanate (BaxSr1-xTiO3):" TIMOTHY E. GLASSMAN, Thomas H. Baum, Stephen M. Bilodeau, Ralph J. Carl, Peter C. Van Buskirk, Advanced Technology Materials Inc., 7 Commerce Dr., Danbury, CT 06810

Intense effort is being expended to incorporate the high dielectric constant oxide barium strontium titanate (BST) into future generation high density DRAM devices. The screening of organometallic precursors for optimization of MOCVD film growth can be accelerated by the development of techniques that simulate the transport and deposition conditions. The thermal stability and decomposition chemistry of the Group 2 compounds [M(thd)2]x (M=Ca, Sr and Ba; thd = 2,2,6,6-tetramethylheptanedionate) and the titanium reagents Ti(O-i-Pr)2(thd),[TiO(thd)2]2 and Ti(O- i-Pr)4 were examined in the presence of argon, oxygen, nitrous oxide and water vapor. The conversion reactions were monitored using techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X-ray diffractometry (XRD), Nuclear Magnetic Resonance (NMR) and C,H elemental analysis (EA). The precursor reactivities are correlated with the compositions of BST films (<1000 è) grown in a liquid delivery CVD reactor and analyzed by XRD and X-ray fluorescence (XRF) spectroscopy.

In argon, all of the Group 2 and Ti precursors undergo simple sublimation; over extended periods of time at 300deg.C slow decomposition is observed. Upon thermolysis in the presence of oxidizing co-reactant gases used in the MOCVD process, a number of reactivity patterns are observed. In oxygen, the Group 2 precursors decompose to their respective carbonates MCO3; this process begins at temperatures as low as 150- 200deg.C. The subsequent evolution of CO2 to form the metal oxides MO does not occur until elevated temperatures of greater than 600deg.C. In the presence of water vapor, the corresponding metal oxides may be formed more readily. The dehydration of the metal hydroxides M(OH)2 to the metal oxides MO occurs at temperatures of greater than 350deg.C. The reaction of precursors with nitrous oxide is also described and compared to oxygen and water.

These results suggest that (i) premature decomposition and gas phase nucleation may be problematic in the presence of high oxygen partial pressures, (ii) the use of nitrous oxide may decrease premature gas phase reactions, resulting in more efficient oxide growth at the higher substrate temperatures and (iii) decomposition of reagents in the presence of water vapor may allow for low temperature deposition of BST thin films.

9:20AM, X4

"Growth and Characterization of CsLiB6O10 Thin Films Prepared by Pulsed Laser Deposition:" J.S. YEO, Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305; A. Akella, L. Hesselink, Department of Electrical Engineering, Stanford University, Stanford, CA 94305

Recently borate crystals have attracted much interest for ultraviolet nonlinear optic application. Cesium lithium borate (CsLiB6O10) is a promising new nonlinear optical crystal which exhibits excellent nonlinear optical properties and simplicity in growth compared to barium borate ([[beta]]-BaB2O4) and lithium barium borate (LiB3O5). Fabrication of CsLiB6O10 (CLBO) thin film is especially interesting to form efficient waveguide for applications such as integrated optic frequency converters and modulators in the ultraviolet region. In this presentation, we report the preparation of crystalline CLBO thin films by using a pulsed laser deposition technique (PLD), which is a versatile technique to grow such complex oxide film since it can easily provide the stoichiometric transfer of target compositions to the substrate with good film quality.

CLBO thin films have been grown on Si (100) and (111) substrates using lower index SiO2 and CaF2 as buffer layers by pulsed KrF (248 nm) excimer laser ablation of stoichiometric CLBO target. CaF2 was chosen to provide good lattice match with Si (0.6%) and with CLBO (4.1%) while CaF2 layer, of which the refractive index is smaller than the value of CLBO, can form a cladding layer for waveguide structure. Substrate temperature was varied from 425deg.C to 725deg.C and its effect on crystallographic orientation and crystalline quality was investigated using x-ray diffraction 20-scans and phi scans. The oxygenpressure was set to 10-2 mbar for growth and 1 mbar during the cooling process to minimize the absorption due to oxygen deficiencies. Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy were used to verify the compositional fidelity between target and film. Atomic force microscopy showed smooth surface morphology with the roughness of a few nanometers. The refractive indices and optical loss of the layers were investigated by the prism coupling method and their optical properties will be discussed.

This research is supported by Navy Grant No. N00014-92-J-1903 through the Center for Nonlinear Optical Materials, Stanford University.

9:40AM, X5

"Hydrothermal Growth of Low-Defect Photorefractive Materials:" J.J. LARKIN, M.T. Harris, D.E. Davies, Rome Laboratory, RL/ERX, Hanscom AFB, MA 01731; J.J. Martin, Dept. of Physics, Oklahoma State University, Stillwater, OK 74078

Bismuth silicon oxide (BSO) and bismuth titanium oxide (BTO) have been grown by the high temperature, high pressure hydrothermal solution growth technique. Heretofore, only Czochralski (CZ) BSO and top-seeded solution grown (TSSG) BTO have been available. Hydrothermal crystals of both compounds exhibit different defect behavior than CZ or TSSG crystals. BSO crystals grown in sodium hydroxide solutions are colorless when the nutrient used is stoichiometric BSO, or when excess silica is added to the nutrient. These water-clear crystals, contrasting sharply with the orange/brown color of CZ BSO, are not photoconductive. If excess bismuth oxide is added to the hydrothermal nutrient, both the color and the photoconductive and photorefractive behavior are restored. This lends credence to the assignment of a bismuth on silicon antisite as the photoconductive site in CZ material.

BTO was grown hydrothermally from a sodium/potassium hydroxide solvent. Crystals are colored when grown from stoichiometric BTO, but the optical absorption is considerably less than that of brown/orange BTO grown by (TSSG). Adjustment in the bismuth oxide/titanium oxide ratio in the nutrient might also be expected to lead to control of the optical absorption tail in this material.

Hydrothermal growth conditions and both optical and electronic defect characterization of both materials will be presented, including optical absorption, thermally stimulated current, and photorefractive results.

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