Novel Materials and Processes
Wednesday, April 12, 2000 8:30 AM in Room Sunrise
H4-1 An Emerging Role of Pulsed Laser Deposition in Growth of Wide Band Gap Metal-oxides and Ill-nitrides for Optoelectronics and High Temperature Devices
R.D. Vispute (University of Maryland)
Wide band gap semiconductors such as III-V nitrides, ZnO, and SiC have now been recognized as potential materials for the generation of optoelectronic devices, high-temperature and high-power devices. The thin film growth techniques generally employed for these materials are chemical vapor deposition, vapor phase epitaxy, and molecular beam epitaxy. We have employed pulsed laser deposition (PLD) technique for the growth of wide band gap oxides and nitrides. The crystalline and optical properties of the PLD GaN, AlN and ZnO films have been shown to be comparable to those grown by MOCVD and MBE. In my talk, I will focus on advances and novel features of PLD technique exploited for the fabrication of high quality thin films, multi-layer heterostructures, optically pumped UV-Blue lasers, quantum wells, and metal-insulator-semiconductor (MIS) devices of wide band gap semiconductors such as ZnO, GaN, AlN, Ga(1-x)Al(x)N, ZnO, and Z(1-x)Mg(x)O. The deposition process, influence of processing conditions on the defects, microstructure, recrystallization kinetics, surfaces and interfaces, and optoelectronic properties of the films will be discussed. I will also present an example wherein PLD AlN as a dielectric on SiC MOSFET devices has exhibited world record leakage currents at temperatures as high as 450C and demonstrated superior properties than thermally grown SiO2 dielectrics. Lastly, issues such as integration of technologically important materials with the III-V nitrides and metal-oxides (ZnO/GaN heterostructures) for fabrication of UV-blue lasers and in-situ epitaxial TiN low resistance ohmic contact metallization on GaN and SiC devices will be discussed. INVITED TALK FOR SYMPOSIUM H, SESSION
H4-3 Nitride Thin Films Grown by Pulsed Laser Deposition Assisted by Atomic Nitrogen Beam.
F.E. Fernández, E. Rodríguez, T. Guzmán, W. Jia, A. Martínez (University of Puerto Rico)
Pulsed Laser Deposition of nitride semiconductors offers an alternative to typically employed growth techniques, such as MOCVD and MBE. PLD can produce good quality thin films at reduced growth temperatures. Growth of these materials requires provision of excess nitrogen in a reactive form during deposition. In our approach, we provide the reactive nitrogen by a low-energy atomic beam. This has the advantage of reducing dependence on substrate temperature to surmount the kinetic barrier for compound formation while avoiding a source of hydrogen during growth. Good quality films were successfully produced for InN, from metallic indium targets, for GaN, from both metallic gallium and ceramic GaN targets, and for AlN, from ceramic AlN targets. Films were grown on sapphire, silicon, and glass substrates. Plume wandering occurring in some cases was effectively deterred by a dual-beam technique. Characteristics determined for our nitride films include composition, crystal structure and orientation, surface morphology, optical properties, and electronic properties of unintentionally doped samples. Luminescence spectroscopy studies were conducted for the films. We report also on our results for high-indium content InGaN thin films obtained by this growth technique. @Footnote 1@This work is supported by NASA, under Grant NCCW-0088, and by the U.S. Office of Naval Research, under Grant No. N00014-96-1-0929.
H4-7 Recent Advances in Pulsed Laser Deposition of Thin Films
K.S. Harshavardhan, H.M. Christen, S.D. Silliman (Neocera, Inc.)
Pulsed Laser Deposition (PLD) has become a rapid prototyping technique of choice in many research laboratories. The phenomenal success achieved with this technique has been demonstrated in numerous applications of multi-component metal-oxide heterostructures incorporating high temperature superconductors, ferroelectrics, electro-optical materials and colossal magnetoresistive oxides. Recent advances made in PLD equipment now permit deposition over large areas, high throughput and deposition on both sides of the substrate. Advances made in ion beam-assisted PLD now allow the growth of single-crystalline-like films on polycrystalline or amorphous substrates, thus broadening the choice of materials for new device applications. While the oxide thin film research community continues to advance PLD, this versatile deposition technique is beginning to penetrate emerging areas such as wide band gap III-V semiconducting nitrides (GaN and AlN), ultra-thin gate oxides and exotic nitride-oxide heterostructures (AlN/ZnO). This talk will review the advances mentioned above and will draw specific materials examples where applicable.
H4-9 Electrochemical Deposition of Barium Titanate Films
F.H. Lu, C.-T. Wu, C.-Y. Hung (National Chung Hsing University, Taiwan, R.O.C.)
Barium titanate films were prepared by a computer-aided electrochemical method. In the deposition system four different operation modes including constant current and voltage as well as scanning current and voltage were completed. After performing different processing conditions with mainly a constant current mode in which the total charges were fixed to be 432 C and the currents were varied from 5, 10, 20, 30, to 40 mA, we successfully prepared single phase BaTiO@sub 3@ films. Polycrystalline BaTiO@sub 3@ films were synthesized by the gavanostatic anodization of Ti in the optimized conditions, i.e., in a solution of 0.35 M Ba(CH@sub 3@COO)@sub 2@ and 2 M NaOH. The pH value was about 13.5. X-ray diffraction results showed that the single cubic phase was formed at 55@super o@C under atmospheric pressure in an oxygen flux. The thickness of the films could reach 15 µm, which is much thicker than that reported in the literature for the corresponding deposition processes. An intermediate phase TiO@sub 2@ phase was identified for the growth of the film. The formation mechanism of BaTiO@sub 3@ films has also been discussed.
H4-10 Fire Retardant Coatings Deposited Using Remote Plasma Polymerization of Organosilicon Monomer
A. Quede (Laboratoire de Génie des Procédés d’Interactions Fluides Réactifs-Matériaux, France); C. Jama, M. Le Bras, R. Delobel (Laboratoire de Génie des Procédés d’Interaction Fluides Réactifs-Matériaux, Ecole Nationale Superieure de Chimie de Lille, France); L. Pawlowski, O. Dessaux, P. Goudmand (Laboratoire de Génie des Procédés d’Interactions Fluides Réactifs-Matériaux, France)
Polymers are intrinsically flammable. For some applications, it is important to render their flammability smaller or to give them flame retardancy property. In the present paper, this property is achieved by a surface modification. It consists of a synthesis of thin film on a polyamide 6 (PA-6) polymer using plasma assisted technique. The plasma applied in the present case is Cold Remote Nitrogen Plasma (CRNP). This process is used to deposit thin film by a reaction of decomposition of 184.108.40.206-tetramethyldisiloxane (TMDS) precursor. Polysiloxane polymers are known to have good thermal stability properties. Different conditions of the deposition process were studied. The influence of parameters such as oxygen flow rate, TMDS flow rate and deposition time were investigated. The flame retardancy of the coated PA-6 was tested using oxygen consumption calorimetry (cone calorimeter). The Rate of Heat Release (RHR), the Volume of Smoke Production (VSP) and the production rate of CO and CO @sub 2@ versus time were compared for uncoated PA-6 and coated PA-6 substrate. The coated PA-6 presents better flame retardancy properties in comparison to the uncoated PA-6 sample. Indeed, the RHR values obtained for the coated samples are 30 % lower. Moreover, it is shown that the coating on PA-6 leads to a less complete combustion reaction.
H4-11 Low Pressure Plasma Spray Coatings
E.J. Young, E. Mateeva, B. Mishra, J.J. Moore (Colorado School of Mines); M. Loch (Sulzer Metco AG, Switzerland)
A new technique - low pressure plasma spray (LPPS) has been used for deposition of good quality Al2O3 coatings on Al for many different applications. Here we present initial results on the properties of the LPPS alumina coating. Chemical compositional analysis by scanning neutral mass spectroscopy (SNMS) and X-ray photoelectron spectroscopy (XPS) shows that the coatings are close to stoichiometric with oxygen to aluminum ratio of 1.65. The cross-sectional transmission electron microscopy and X-ray diffraction investigations revealed that the structure of the coating is complex: quasi-layered splat structure with splats consisting of a polycrystalline core embedded in an amorphous matrix. Initial dielectric measurements show dielectric strength of about 400 V/cm in some of the coatings, a value significantly higher than in thermal spray coatings. We relate dielectric strength to the microstructure of the coatings and realistic pore distribution determined both by mercury porisometry and electron microscopy imaging. The studies of the adhesion of the coating to the Al substrate using scratch testing showed maximum adhesion (critical loads) for the 20 micron thick coating. This finding has been related to the microstructure of the coating and the initial substrate preparation. The effect of different substrate surface preparation on improving adhesion is being investigated.