Thin film(s) of chalcopyrite CuInE2(where E = S or Se) have been grown by low-pressure metal-organic chemical vapour deposition (LP-MOCVD) using the precursors [In(E2CNMenHexyl)3] and [Cu(E2CNMenHexyl)2]. Similarly, thin films of ME (where M = Zn, Cd; E = S, Se) have been deposited from precursors of general formula [M(E2CNMenHex)2]x. Films were grown on glass between 400 - 500 °C, and characterized by X-ray diffraction, optical spectroscopy (UV/Vis), EDAX and scanning electron microscopy.

We have been working on the development of wet-chemical processing methods that can be used to create thin film photovoltaic solar cells. Electrochemically deposition methods have been used to produce copper indium diselenide (CIS) thin films on molybdenum coated polymer substrates. CIS has an extremely high optical absorption coefficient, excellent radiation resistance, and good electrical conductivity and thus has proved to be an ideal absorber material for thin film solar cells. A series of compositionally different p-type CIS films were produced by using different electrochemical deposition potentials. Cadmium sulfide (CdS) window layers were deposited directly on these CIS films using a chemical bath process. CdS is a naturally ntype wide-bandgap semiconductor which has good transparency and is well lattice-matched to CIS. Zinc oxide thin films were grown by electrochemical deposition directly on the CdS films. ZnO is a transparent and conductive thin film that serves as the top contact of the cells. The structural and elemental properties of the individual ZnO, CdS and CIS films were characterized by x-ray diffraction and energy dispersive spectroscopy. The electrical behavior of the CdS on CIS junctions was determined using current versus voltage measurements. We will discuss the performance of these devices based on the physical properties of the component films and the processing methods employed in their fabrication.

Titanium oxide (TiO2) thin ftlms were formed on a Si substrate by metalorganic decomposition(MOD) at temperatures ranging from 600 to 1100°C. As-deposited films were in the amorphous state and were completely transformed after annealing at 600°C to a crystalline structure with anatase as its main component. During crystallization, a reaction between TiO2 and Si occurred at the interface, which resulted in the formation of a thin interfacial SiO2 layer. Capacitance-voltage measurement showed good dielectric properties with a maximum dielectric constant of 76 for films annealed at 700°C. For the crystallized TiO2 films, the interface trap density was 1 × 1011 cm−2 eV−1, and the leakage current was 1 × 10−8 A/cm2 at 0.2 MV/cm. The modified structure of TiO2/SiO2/Si is expected to be suitable for the dielectric layer in an integrated circuit in place of conventional SiO2 films.

High quality barium titanate films were grown on (001)LaAlO3 and r-Al2O3 in a wide thickness range of 0.5-10 µtm by sol-gel technique. Significant improvement of the films' crystallinity and optical quality was observed if acetate precursors are used vs. alkoxide precursors, and in the presence of lead oxide. The material is transparent at 350-2000 nm, indicating the possibility of its application in light controlling devices at wavelengths used in optical communication: 1300 and 1500 nm. Maximum field induced relative phase shift of 0.22 radian was measured in the film with composition of Ba0.9Pb0.1TiO3 under a field strength of 3.106 V/cm.

Barium strontium titanate with low dielectric constant, low loss tangent and high tunability, has unique application as phase shifter in radar and antenna. This work presents an alternative fabrication of the composite of barium strontium titanate with metal oxides such as Al2O3 and MgO. Ba1−xSrxTiO3 (BST), xergels of various compositions (x = 0.2, 0.4, 0.5 and 0.6) were prepared by sol-gel method. Xerogels were calcined at 800 °C. The structure of the final powders was investigated by x-ray diffraction (XRD). The resultant BST was then mixed with metal oxides in the desired weight percentage and ball milled in an organic solvent (ethyl alcohol) with a binder (acrylic polymer). The final samples were sintered at 1250 °C in air. The dielectric properties of the composites were determined by using impedance analyzer at the frequency of 1MHz. This work has reported the effect of Al2O3 and MgO, on the electronic behavior of the final BST-metal oxide composites.

BaTiO3 and PZT films were prepared by single-step dip-coating from alkoxide-acetate solutions containing polyvinylpyrrolidone (PVP). Crack-free BaTiO3 and PZT films over 1 μm in thickness were obtained via single-step deposition. Stepwise heating of the gel films was found to improve densification of BaTiO3 films, reducing the thickness and increasing the optical transmittance, which was not, however, the case with PZT films, where the stepwise heating rather induced crack formation, leading to degraded transmittance. Residual stress was evaluated on spin-coating BaTiO3 films by measuring the substrate curvature, where a significant reduction in tensile stress was found to be caused by PVP.

Barium-deficiency of barium titanate particles prepared by low temperature hydrothermal reaction has been notorious. It has been believed that barium-deficiency is caused by the high solubility of barium source compared with titanium. Here is reported the synthesis of nearstoichiometric barium titanate powders with ultrafine particle size and high crystallinity by low temperature hydrothermal reaction from barium acetate and titanium tetra(methoxyethoxide). Barium titanate particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60 ∼ 90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor. Increasing barium to titanium molar ratio in reactant could not overcome the notorious barium-deficiency but, improved stoichiometry and produced finer and less agglomerated particles. Interestingly, adding a slight pressure to autogeneous one to make total 4 ∼ 10 atm has yielded near-stoichiometric, highly crystalline, and less agglomerated barium titanate particles. It seems like that the total pressure around 4 ∼ 10 atm provides strong force enough to push barium ions into the interstitial points of perovskite structure and stabilize it. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at 400 °C.

We have been studying new approaches to conventional Chemical Bath Deposition (CBD) of chalcogenide containing materials, using continuous circulation and replenishment of CBD solution over a heated substrate. Crystalline thin films produced by this method offer potential for use in solar cell devices or other optoelectronic applications. Films of CdS, ZnS and the ternary material CdxZn1−xS have been deposited on TO-glass substrates. In this paper we demonstrate our approach for the deposition of CdS films. These have been characterized by XPS, SEM, XRD and UV/vis spectroscopy and shown to be good quality. The films have been used to fabricate Au/CdTe/CdS/TO-glass solar cells of efficiency 10.1% under AMl.5 illumination.

Application of Soft Solution-Processing, which is defined by environmentally friendly processing using (aqueous) solution, to the field of rechargeable lithium microbattery has been demonstrated by fabricating LiCoO2 film on the cobalt metal substrate in LiOH solution under hydrothermal condition. The film formation mecahnism could be interpreted in terms of chemical dissolution of cobalt metal plate in LiOH solution at fixed temperature of 20 - 200°C, resulting in the formation of H1−nCoO2 where n value increases with fabrication temperature and precipitation as LiCoO2 by heterogeneous nucleation on the substrate followed by crystal growth. The crystal structure and film properties have been characterized by X-ray diffraction, X-ray photoelectron, micro-Raman spectroscopic and scanning electron microscopic analyses. The films exhibited a good crystallinity despite the low reaction temperature without any postsynthesis annealing. The films prepared under different conditions showed different phase selection such as spinel (Fd3m) or hexagonal (R3-m), surface morphology and film thickness. An electrochemical activity of the LiCoO2 films was evidenced by cyclic voltammogram revealing a good reversibility on Li-intercalation and -deintercalation.

In the present work we have optimized the process parameters to yield homogeneous, smooth ruthenium oxide (RuO2) thin films on silicon substrates by a solution deposition technique using RuCl3.×.H2O as the precursor material. Films were annealed in a temperature range of 300°C to 700°C, and it was found that RuO2 crystallizes at a temperature as low as 400°C. The crystallinity of the films improves with increased annealing temperature and the resistivity decreases from 4.86µΩ-m (films annealed at 400°C) to 2.94pµΩ (films annealed at 700°C). Ageing of the precursor solution has a pronounced effect on the measured resistivities of RuO2 thin films. It was found that the measured room temperature resistivities increases from 2.94µΩ-m to 45.7µΩ-m when the precursor sol is aged for aged 60 days. AFM analysis on the aged films shows that the grain size and the surface roughness of the annealed films increase with the ageing of the precursor solution. From XPS analysis we have detected the presence of non-transformed RuCl3 in case of films prepared from aged solution. We propose, that solution ageing inhibits the transformation of RuCl3 to RuO2 during the annealing of the films. The deterioration of the conductivity with solution ageing is thought to be related with the chloride contamination in the annealed films.

Sol-gel synthesis of transitional metal oxides is one of the important technique to obtain the pure and homogenous materials at low temperature. In this work, Barium strontium titantate (BST) was synthesized by sol-gel processing using 2,4-pentadionate as the precursors of metal oxides. The Ba1−xSrxTiO3 was prepared for four values of x i.e. 0.2, 0.4, 0.5 and 0.6. The obtained powders were heated from 400 °C to 800 °C at the interval of 100 °C to determine the temperature of crystallization. The phase of the final products was investigated by x-ray diffraction (XRD). Two particle sizes (< 100 nm and 200-400 nm) were observed under the scanning electron microscope (SEM) of the heat treated xerogel. The dielectric properties were determined by impedance analyzer at the frequency of 1MHz and explained in detail for the different values of x.

There is interest in lithium intercalation oxide materials for cathodes in rechargeable batteries. We have synthesized LiMOx, (where M = Mn, Co) by a less expensive solution route. Reagent grade acetates or hydroxides as precursors for lithium, manganese, and cobalt, respectively, with methoxy ethenol and acetic acid as solvents were used. Powders with different compositions were achieved at annealing temperature below 700 °C. Thin films were deposited by spin coating. X-ray diffraction, Raman spectroscopy, and impedance spectroscopic results are presented. These studies indicate that this synthetic route is suitable to produce good quality lithium-based oxides useful for cathode in lithium-ion rechargeable battery.

Crack-free La0.2Sr0.8CoO3−x (LSCO) membranes have been fabricated on porous ceramic supports such as MgO and CeO2 through dip coating and sintering. To avoid cracks in a LSCO membrane during sintering, a silver coating on top of the LSCO powder-packed layer that is formed via dip coating was found successful. The cracks would be otherwise unavoidable due to the shrinkage mismatch between the membrane and the support during sintering. The silver can be readily removed from the sintered LSCO membrane chemically without causing damages in the membrane.

Powders of LaGaO3, La0.9Sr0.1GaO2.95 and La0.8Sr0.2Ga0.83Mg0.17O2.815 were prepared by the amorphous citrate/EG method. The calcination behavior of the precursor powders of the above phases were studied in the temperature range of 200°-1400°C, in an air atmosphere. Characterization of the samples were performed by XRD, TG/DTA, FTLR, SEM, ICP-AES, and carbon and nitrogen analyses.

An alkaline aqueous silicon wafer cleaner has been developed which reduces trace metal contamination levels on “p-type” unpatterned silicon wafers to below 1E10 atoms/cm2 without acidic cleaning. This patented technology uses a specially formulated buffering system consisting of an oxidation resistant chelating agent and salt of a weak acid. The aqueous cleaner maintains a stable pH of about 9.5 over a wide range of dilutions, temperatures, hydrogen peroxide concentrations and bath aging times. A single-step bath, megasonic bath or spray clean with this formulation leaves the chemical oxide on the silicon wafer surface free of particles, atomically smooth, free of organics and lower in trace metal contamination levels than similar surfaces cleaned with conventional formulations.

An analytical method was developed which allows the reliable detection of trace metals on silicon wafer surfaces down to 1E8 atoms/cm2 for aluminum, calcium, copper, iron, nickel, sodium and zinc. The procedure uses an ICP-MS with a concentric nebulizer and a desolvator. The acids used were ultrapure to keep the blanks to a very minimum and analyses were run in a class 10 clean room. The trace metals on the wafer were extracted using known amounts of ultrapure acids and were directly aspirated using a special arrangement with the concentric nebulizer. The J.T. Baker cleaner was compared to and outperformed the conventional RCA-1&2 clean and dilute RCA-1&2 chemistries using ultrapure ammonium hydroxide, hydrochloric acid and hydrogen peroxide.

Silsesquioxanes containing β-acetoxyethyl (BAE) groups are processible resins that can be employed as spin-on-glass precursors to dielectric silica films. Thermal treatment >250 °C results in extrusion of ethylene from the CH2CH2OCOCH3 moiety with formation of Si- OCOCH3 groups, which undergo facile hydrolysis to a silica network. A minor pathway involving extrusion of acetic acid leaves some silicon vinyl groups, leading to residual organic carbon in the material. However, addition of a fluoride ion catalyst greatly accelerates the major reaction, resulting in lower conversion temperatures (<200 °C), quantitative extrusion of ethylene, and essentially pure silica. Alternatively, BAESSQs can be processed photochemically (λ <200 nm) to cleanly yield silica at ambient temperature.

Etch rates up to 1200 Åmin−1 for Ta2O5 were achieved in both SF6/Ar and Cl2/Ar discharges under Inductively Coupled Plasma conditions. The etch rates with N2/Ar or CH4/H2/Ar chemistries were an order of magnitude lower. There was no effect of post deposition annealing on the Ta2O5 etch rates, at least up to 800 °C. Selectivities to Si of ∼1 were achieved at low source powers, but at higher powers the Si typically etched 4-7 times faster than Ta 20 5. UV illumination during ICP etching in both SF6/Ar and Cl2/Ar produced significant enhancements (up to a factor of 2) in etch rates due to photo-assisted desorption of the TaFx products. The UV illumination is an alternative to employing elevated sample temperatures during etching to increase the volatility of the etch products and may find application where the thermal budget should be minimized during processing.

Reactive-magnetron-sputtered ZrO2 thin film has been deposited on Si directly for gate dielectric application. Both structural and electrical properties of the ZrO2 film have been investigated. An amorphous structure for 30Å ZrO2 and a semi-amorphous structure for 200Å ZrO2 have been revealed. The sputtered film shows a good stoichiometry and a good structural stability of ZrO2 based on the X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy data. Thin equivalent oxide thickness of about 11.5Å was obtained without the consideration of quantum mechanical effects. A low leakage of less than 10−2 A/cm2 at ±1V relative to the flat band voltage was obtained for this 11.5Å equivalent oxide thickness Pt/ZrO2/Si structure. High effective dielectric breakdown and superior reliability properties have been demonstrated for ZrO2 gate dielectric.

Hysteresis effect of barium strontium titanate (BST) thin films for gate dielectric application has been studied. It is found that the “counterclockwise” hysteresis has strong sweep voltage and operating temperature dependence. It can be reduced or eliminated by proper thermal annealing or by using a barrier layer. A charge trapping and detrapping mechanism has been proposed.