This paper discusses the behavior of currents and fields along a structured superconductor. First the effect of surface structure on supercurrents is investigated. Then the effect of structure on the critical nucleation field is discussed in two cases, one with the magnetic field parallel to the ripples and the other with the field parallel to the grating wavenumber. In the first case, it is found that the critical field is reduced as a function of grating height, whereas in the latter case it is increased. Finally, the relevance of this work for laser-induced chemistry above a superconducting surface is discussed. The Ginzburg-Landau model is used throughout.

Photoexcitation effects of GaAs vapor phase epitaxy have been studied. The growth rate is enhanced by irradiating the substrate zone with an exciier laser irradiation at 2 4 9 n m wavelength, however, the growth rate is reduced by irradiating the source Ga zone with a 249 or 222m exciier laser at températures below 650*C. Because of sharp wavelength dependence and from the result of the theoretical estimations, these effects have been concluded to be caused not by a therma1 -induced reaction but, rather, by photoinduced reactions.

Influence of photoexcitation of the film grown by molecular layer epitaxy has been also studied. Photoirradiation could be independently undertaken at different crystal growth steps, e.g. the irradiation duration could be synchronized with the time duration of each gases supply and exhaust. By this method “synchronized irradiation”, the quality of the epitaxial film and the surface morphology of epitaxial films grown by molecular layer epitaxy were improved.

Selective epitaxial growth of III-V compounds based on GaAs has been achieved using Ar+ ion laser assisted chemical vapor deposition (LCVD) on GaAs substrates. The growth rate, at carefully selected growth conditions, can be controlled to a few Å/s at bias temperatures as low as 250°C by conventional LCVD multi-scan technique. Typical Gaussian thickness profiles are achieved by this growth technique. On the other hand, flat top thickness profiles are achieved with direct writing of GaAs mono-layers by laser assisted atomic layer epitaxy (LALE). X-ray topography is demonstrated as a powerful tool for characterizing the grown films and photoluminescence shows that the quality of the grown films are comparable with those grown by conventional MOCVD or ALE.

We report the growth of GaAs by laser-assisted molecular beam epitaxy, using As4 and either elemental Ga or triethylgallium (TEG) sources, and a 193 nm ArF excimer laser. Laser irradiation of (Al)GaAs has no effect on the growth rate or Ga-to-Al incorporation, when GaAs substrates and elemental group-III sources are used. When GaAs is grown from TEG, laser irradiation results in a selective-area film growth at temperatures below 450°C, where growth due to pyrolytic decomposition of TEG is very slow. The process is extremely efficient, with roughly unit probability for impinging TEG molecules sticking and being dissociated by laser radiation to form GaAs. From the strong dependence on laser fluence, the growth enhancement process appears to be pyrolytic in nature (due to rapid transient healing by the pulsed laser), and not photolytic. The cross section for photolysis must be at least ten times lower than the gas-phase value (9x10-18cm2). Using either Ga source, laser irradiation improves surface morphology and photoluminescence yields, compared to areas receiving less intense laser radiation.

In growth of GaAs from elemental sources on (Ca, Sr)F2 lattice-matched to GaAs, laser irradiation inhibits growth due to laser-induced thermal desorption of adsorbed Ga atoms, which are relatively weakly bound to (Ca,Sr)F2 compared to GaAs surfaces.

Laser ionization mass spectrometry has been used to study the deposition of gallium from trimethylgallium with and without AsH3. The apparent Arrhenius activation energy for the production of gas-phase methyl radicals from trimethylgallium is measured to be 28 ± 2 kcal/mol in the presence of AsH3, about the same value as measured in the absence of AsH3. At a substrate temperature of 1150 K where gallium desorption is substantial, addition of AsH3 is found to increase methyl radical yield but drastically decrease gallium atom desorption. A mechanism is presented to describe the deposition of GaAs at low pressures under single gas-surface collision conditions.

Triisobutylaluminum (TIBA) was used as an aluminum source for metalorganic molecular beam epitaxy (MOMBE). The optical absorption coefficient for TIBA was found to be larger than both tri ethyl aluminum and triethylgallium. TIBA was introduced into a laser-induced MOMBE system and selective deposition of Al and AlAs was carried out. Al metal was deposited on the area where the ArF excimer laser was irradiated and no deposition was observed without the excimer laser irradiation at a substrate temperature of 350 C. Furthermore, a laser large enhancement of the growth rate of AlAs was observed at 350 C.

Films of InSb were deposited on GaAs <100> substrates at room temperature by excimer laser photolysis at 193 or 248 m of a mixture of trimethylindium (TMIn) and trimethylantimony (TMSb) in a hydrogen carrier medium. These films were compared to thermally grown MOCVD InSb films by optical microscopy and x-ray analysis and found to be stoichiometric polycrystalline, InSb. In situ UV absorption spectroscopy has been used for the first time on an MOCVD system to monitor and control the partial pressures of the metalorganic reactants during deposition. This latter diagnostic was found to be critically important since parasitic reactions cause depletion of TMIn during transport from the source bubbler to the growth chamber.

Excimer laser-assisted MOVPE has been used to deposit thin films of CdTe (111) on GaAs (100) substrates. Auger spectroscopy indicates that the films are stoichiometric and that carbon and oxygen contamination are below the levels of detectability. Good crystalline quality of the layers is confirmed by x-ray diffractometry. Growth rates up to 2 /μm/hr have been recorded in real time using time-resolved reflectivity. The CdTe growth rate is found to have a linear dependence on reactant partial pressure and laser average power, but was independent of substrate temperature in the range of 150° C to 300* C. Laser-induced fluorescence spectroscopy has been used to determine that photolysis of diethyltellurium at 248 nm is a one photon process which produces ground state Te atoms. The flux of reactive species to the substrate surface has been probed by mass spectrometry. Evidence for the generation of monoethyltelluride, either by recombination or direct photolysis, is presented.

The UV photodissociations of dimethyltelluride (CH3)2Te and diethyltelluride (C2Hs)2Te have been investigated by state-selective detection. Nascent populations of Te(5p Pjw) atoms produced by the photodissociation process were monitored using laser-induced fluorescence following excimer laser (248 nm and 193 nm) photolysis. Experimental results for both molecules indicate that the photolysis at 248 nm produces Te atoms via a single photon process and that the liberated Te atoms populate only the 5p3P2 state. The photolysis of diethyltelluride at 193 nm has also been found to be a single photon process producing Te atoms distributed over the 3P2, 3P1, and Pø states in a ratio of 13:2:1, respectively.

Experimental studies of the thermal and photon-induced surface chemistry of two organometallic molecules, dimethyl cadmium and dimethyl tellurium, are reported for a variety of surfaces including Au, GaAs, Si, and SiO£. These studies followed ultrahigh vacuum compatible procedures and used x-ray photoelectron spectroscopy to characterize the chemical state and coverage of the adspecies formed at 295 K. The results showed considerable diversity in the thermal surface chemistry of the systems investigated. Depending on the substrate, physisorption and dissociative chemisorption to yield monomethyl and metal adspecies were observed. Irradiation of the physisorbed adspecies with 193 nm UV photons led to single photon photodecomposition and limited photodesorption. Similar irradiation of the monomethyl-adspecies caused only limited photodesorption.

CdSxSe1−x thin films have been grown by uv laser-evaporation deposition in a clean vacuum environment. The films have their c-axis perpendicular to the surface, and are optically smooth and homogeneous. These high quality films should be useful in nonlinear integrated optics applications.

Thin films of the new class of high temperature superconducting perov-skites have been prepared by laser ablation of t,he bulk materials with a pulsed, excimer laser operating at 193 nm. The films were deposited on room temperature substrates without post-deposition processing. The existence of superconducting regions in the inhomogeneous films was established by a novel microwave method which uses a slightly modified electron spin resonance spectrometer.

Epitaxial Ge films have been grown on [001] GaAs for substrate temperatures (Ts) as low as 285°C by photodissociating GeH4 at 193 nm in parallel geometry. For a laser fluence of ~15 mJ - cm-2, the film growth rate varies from 0.6 to ~5 nm - min-1, depending upon Ts and gas pressure. Plan and cross-sectional TEM studies of the Ge/GaAs bicrystal demonstrate that the 400–700 A thick Ge films are single crystal and epitaxial with the substrate. The present limitation on epitaxial film thickness appears to be imposed by reduced adatom mobility at the temperatures investigated.

Pulsed ArF (193 nm) excimer laser radiation has been used to dissociate disilane (Si2H6), resulting in photochemically controlled deposition of amorphous Si thin films. A high stability HeNe (6328 Å) laser was used for precise in situ monitoring of film deposition rates, under varying deposition conditions. A helium window purge nearly eliminated Si film deposition on the chamber windows. With the excimer laser beam parallel to the substrate, deposition of amorphous Si can be controlled entirely by the photon fluence (negligible background thermal growth) at temperatures from room temperature up to ~400°C. Reasonable photolytic deposition rates (>1 A/sec) are combined with "digital" control of film thickness (>0.02 A/laser pulse). Activation energies of 1.50 (±0.1) eV and 0.09 (±0.02) eV were found for pyrolytic and photolytic deposition, respectively.

We have determined for the first time, the two-photon absorption cross-section of silane at 193 nm, by measuring directly the fraction of incident light absorbed in the gas phase during the irradiation with a pulsed ArF excimer laser.

Amorphous carbon (a-C) films were prepared by photodissociation of C2H3Cl or CCl4 gas using a pulsed ArF excimer laser (193nm). An increase in the substrate teiperature decreased the deposition rate. For C2H3Cl4 the maximum deposition rate of 10Å/min was attained at a partial pressure of 0.1 Torr and room temperature. In contrast, for CCl4, the maximum deposition rate of 10Å/Min was obtained at a partial pressure of 3 Torr and room temperature. This difference may be attributed to the different absorption cross sections for the two gases. The structural and mechanical properties were leasured. An Auger analysis showed the chlorine content in the a-C film deposited at room temperature to be 1% for C2H3Cl and 8% for CCl4. The Mohs hardnesses of the a-C filis deposited at room teiperature were 7 and 2 for C2H3Cl and CCl4, respectively. It was concluded that both sp2 and sp3 bonds existed between neighboring C atoms at low temperatures, whereas SP2 bond was predominant at temperatures higher than 300°C.

A photochemical system of mercury-sensitized reactions between silane and ammonia was studied to elucidate the gas-phase chemical processes involved in photo-CVD of silicon nitride. Several transient intermediates were detected and identified as silylated amines by the mass spectrometric isotope labeling method. These compounds containing both Si and N atoms appeared to be the precursors of silicon nitride. The chemical characteristics of silylated amines were studied under different experimental conditions. The reactivity and possible reaction paths for the formation of silylamine are discussed.

Silicon nitride films were deposited using a photochemical vapor deposition method. The defect density in these films was under 100/cm2 and the film adhesion was in excess of 104 psi. No lift-off was observed at power densities of up to 10 A/cm2 at applied voltages of up to 100. The film stress was compressive and under 5x103 psi. Total mobile ion concentration in the films did not exceed 109/cm2. Device analysis was carried out using Motorola dual gate MESFETs. Device degradation was evaluated in terms of surface potential sensitive parameters like source-drain current and resistance, by making comparisons in these parameters before and after passivation. Some degradation (up to 17 %) occurred in some of these parameters subsequent to device passivation. These results are comparable to or better than those encountered in most other low temperature films (like plasma enhanced CVD and polyimide films). The observed device properties are explained in terms of the film composition and the applicability of photo-CVD nitride films for MESFET passivation is discussed.

A photochemical vapor deposition technique was used to deposit silicon oxide films. A range of film properties was produced through changes in the process conditions. Refractive index, indicative of film composition, varied from 1.5 to 2.0, corresponding to oxygen rich and silicon rich conditions, respectively. Etch rate in buffered HF was a strong function of the refractive index, with higher index of refraction yielding lower rates. Film stress was tensile and the magnitude of the stress was again related to the index of refraction. Other properties that were evaluated included pinhole density and adhesion to Si. All the properties were directly relatable to the basic film composition.

X-ray photo electron and Auger electron spectroscopy were used to characterize the composition of these films. The Si 2p photoelectron and the Si KLL Auger electron spectra were broad for higher refractive index films and upon deconvolution indicated the presence of different silicon containing species, the natures of which depended upon the actual index of refraction. For stoichiometric films, the predominant constituent was SiO2 and for non-stoichiometric films, varying amounts of Si2O, SiO, Si2O3 and SiO2 were all present.

Aluminum oxide (A12O3), nitride(A1N) and silicon nitride(SiN) films were prepared at a low substrate temperature of 100°C. Film resistivity was higher than 5x1013 Ω-cm and the breakdown voltage was greater than 3x10° V/cm. The films deposited on sapphire and silicon substrates were very flat, and were chemically and thermally stable. The A1-O, A1-N and Si-N bonds could be formed effectively by using both ionized clusters and reactive gas ions, and transparent and good quality films were obtained. Through these results, the simultaneous use of an ionized cluster beam (ICB) system and a microwave ion source was found to have a high potential for preparing oxide and nitride films at a low substrate temperature.