Photo-assisted MOCVD Research Articles

Higher oxidization rate of photo-assisted annealing compared with thermal annealing after YBa2Cu3O7−δ films growth

In order to study the possible advantage of photo-assisted MOCVD compared with thermal MOCVD during the annealing process after film growth, a piece of c-axis oriented YBa2Cu3O7−δ film on Φ1″ LaAlO3 (100) substrate was prepared by photo-assisted MOCVD. It has well in-plane alignment and high critical current density (Jc>2.5MA/cm2, @ 0T, 77K, thickness≈430nm). Small pieces cut from it were annealed by photo-assisted or thermal annealing process to realize deoxidization or oxidization respectively. By monitoring the c-axis lattice constant, it was found that oxidization rate of photo-assisted annealing is obviously higher than that of thermal annealing. Inversely, the deoxidization rate of photo-assisted annealing is lower than that of thermal annealing. And a phenomenon that the long-time stable c-axis lattice constant is related to the temperature, unrelated to annealing process has been observed. It conforms to the thermodynamic equilibrium which is relative to annealing temperature and oxygen partial pressure, irrespective to whether photo activation or thermal activation.

Thickness Dependence of Structural and Superconducting Properties of Single-Crystal-Like GdBCO Films Prepared by Photo-Assisted MOCVD

High-quality GdBa2Cu3O7-δ (GdBCO) films with thicknesses of 0.14-1.62 μm were deposited on (100)-oriented LaAlO3 substrates by photo-assisted metal-organic chemical vapor deposition technique. Evaluation of film microstructure and strain-relaxation phenomenon in the growing films and their effects on the crystallographic and superconducting properties of the GdBCO films have been investigated. A single-crystal-like cross-sectional morphology with dense and crack-free surface and no grain boundary visible was observed. The c-axis lattice parameters of the GdBCO films grown with different thicknesses were used to determine the out-of-plane strain. The result shows that the strain could be gradually relieved as film thickness increases. Highly biaxially textured GdBCO films have been obtained. For a 0.31-μm GdBCO film sample, the full-widths at half-maximum were 0.08° and 0.47° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single-crystal GdBCO. The highest critical current density (Jc) value is ~ 2.5MA/cm2 (77 K and 0 T). As films were getting thicker, their Jc values decrease gradually. This is mainly attributed to a lack of pinning centers in the thicker films.

Self-assembling of strain-induced Y2O3 nanostructures grown on LaAlO3 by photo-assisted MOCVD

Y2O3 nanodots were fabricated on vicinal substrate (100)-oriented LaAlO3 (LAO) by photo-assisted metalorganic chemical vapor deposition (PhA-MOCVD). Nucleation and growth processes of Y2O3 nanodots self-assembled as rows along the terraces of LAO were investigated with various growth parameters. It is found that density and size of Y2O3 nanodots can be tuned and well controlled by varying substrate temperature (Ts), oxygen partial pressure and growth time. At lower Ts, the morphologies of Y2O3 nanodots are characterized by small and dense solid cones. With elevating Ts, the dots gradually grow larger and sparser. This phenomenon could be illustrated by two competitive kinetic processes, i.e. surface diffusion of adatoms and yttrium desorption. Morphologies of these nanodots were also influenced by variation of oxygen partial pressure. To further discuss the growth kinetics, a more clearly quasi-linear distribution was obtained and the coarsening effect is modified by varying growth time.

Morphology and superconducting properties of photo-assisted MOCVD processed YBCO film by variation of sublimation temperature of the Cu-based precursor

Normally, surface of c-axis oriented YBCO films grown by MOCVD are found to be populated by micron-sized outgrowths with elemental compositions such as Ba–Cu–O and Cu–O. For both low and high current applications with the YBCO films, these surface outgrowths should be eliminated. In this study, it is found that by using a simple processing technique of decreasing appropriately the sublimation temperature of the Cu-based precursor, the surface outgrowths can be essentially subdued. At the same time it is qualitatively predictable that Jc of these smoother YBCO films will be lowered. However, experimentally, it is found that at appropriate YBCO film growth conditions, the lowered Jc value is acceptable for most applications. Actually, a surface outgrowth covered YBCO film made by photo-assisted MOCVD, with film composition Y:Ba:Cu as 1:1.2:1.5, has its Jc being 3.4MA/cm2 (0T, 77K). As composition of YBCO film is changed to 1:0.9:1.2 by lowering the sublimation rate of the Cu-based precursor, then there are no more outgrowths on surface, with its Jc being 2.6MA/cm2.

Nitrogen Doped ZnO Thin Films Prepared by Photo-Assisted Metal-Organic Chemical Vapor Deposition

Nitrogen-doped ZnO (ZnO:N) films were prepared by photo-assisted metal-organic chemical vapor deposition technique using NH3 as N doping source. The effects of in-situ light irradiation on the properties of ZnO:N films were studied by Hall measurements, X-ray diffraction, Raman scattering, and X-ray photoelectron spectroscopy. The results show that stable p-type ZnO:N films with a hole concentration of 3.61 x 10(17) cm(-3) was successfully achieved. Moreover, introducing proper in-situ light irradiation during the growth process can not only effectively improve the crystalline quality of ZnO films, but also enhance the activity of (N)o (N occupies O site) acceptors by removing the undesirable hydrogen atoms from ZnO:N films. Both effects are benefit for the p-type conductivity formation. Our results indicate that photo-assisted MOCVD maybe an effective technology to realize device-quality p-type ZnO:N films.

Fixed-Oxide-Charge Characterization by Photoreflec-tance Spectroscopy in HfO2 on Ge treated by Fluorine

The interface traps in HfO2/Ge is reduced by fluorine treatment, and photoreflectance spectroscopy (PRS) which has some merits such as nondestructive and contactless, is applied for characterization of fixed charges distribution to HfO2/Ge gate stack as a new type of measurement method. C-V characteristics show that the sample treated with fluorine before deposition by photo-assisted MOCVD has small hysteresis, and interface states are improved. PRS signal of HfO2/Ge gate stack can be detected, and these measurements show that fixed charges are mainly distributed at interface and reduced by fluorine treatment.

Precisely determined temperature window size for the growth of high quality c-axis oriented YBCO films by photo-assisted MOCVD

It is well-known that there is a relatively small temperature window for the growth of epitaxial and c-axis oriented YBCO thin films by various methods. In this study, this window was more precisely examined for YBCO film growths by photo-assisted MOCVD. At specified total reactor pressure of 4.6 torr, and specified respective partial pressures for the oxidizing agents, O 2 and N 2O at 1.7 torr and 1.1 torr, the film growths were tested at several substrate temperature ( T s) points from 780 °C to 864 °C. The film growth time for each test was 3 min. As to compositional purity, purity in c-axis orientation, and crystal structural quality of these tested films by using photo-assisted MOCVD technique, it was found that for the growth of purely c-axis oriented YBCO thin films with high crystalline quality, the appropriate growth temperature range (or “ T s window”) was from about 800 °C to 830 °C, at relevant pressures as specified above. T c and J c of a typical YBCO film sample grown within this “ T s window”, i.e., 810 °C, were found as 90 K and 1.32 MA/cm 2 (77 K, 0 Oe) respectively by magnetization measurements. It is noticeable that this film, and other purely c-axis oriented YBCO films are all single-crystal like and dense, with no SEM visible grain boundary or void. The causes of precipitates found on top surface of these c-axis oriented YBCO films are also discussed.

Characteristics improvement of HfO 2/Ge gate stack structure by fluorine treatment of germanium surface

Chemical reactivity of fluorine molecule (F 2)–germanium (Ge) surface and dissociation of fluorine (F)–Ge bonding have been simulated by semi-empirical molecular orbital method theoretically, which shows that F on Ge surface is more stable compared to hydrogen. Ge MIS (metal insulator semiconductor) capacitor has been fabricated by using F 2-treated Ge(1 0 0) substrate and HfO 2 film deposited by photo-assisted MOCVD. Interface state density observed as a hump in the C– V curve of HfO 2/Ge gate stack and its C– V hysteresis were decreased by F 2-treatment of Ge surface. XPS (X-ray photoelectron spectroscopy) depth profiling reveals that interfacial layer between HfO 2 and Ge is sub-oxide layer (GeO x or HfGeO x ), which is believed to be origin of interface state density. F was incorporated into interfacial layer easily by using F 2-treated Ge substrate. These results suggest that interface defect of HfO 2/Ge gate stack structure could be passivated by F effectively.

Properties of ZnO thin films grown on Si substrates by photo-assisted MOCVD

ZnO thin films were grown on (1 0 0) p-Si substrates by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) using diethylzinc (DEZn) and O 2 as source materials and tungsten–halogen lamp as a light source. The effects of tungsten–halogen lamp irradiation on the surface morphology, structural and optical properties of the deposited ZnO films have been investigated by means of atomic force microscope (AFM), X-ray diffraction and photoluminescence (PL) spectra measurements. Compared with the samples without irradiation, the several characteristics of ZnO films with irradiation are improved, including an improvement in the crystallinity of c-axis orientation, an increase in the grain size and an improvement in optical quality of ZnO films. These results indicated that light irradiation played an important role in the growth of ZnO films by PA-MOCVD.

A single oxide buffer layer on a cube-textured Ni substrate for the development of YBCOcoated conductors by photo-assisted MOCVD

Large-scale commercial applications of high-temperature superconducting (HTS)YBa2Cu3O7−x (YBCO)-based second generation coated conductors require simple and cost-effectiveprocess technologies to fabricate the buffer layer(s) and YBCO superconducting layer.Sm0.2Ce0.8O2+x (SCO) thick films have been epitaxially deposited on roll-textured Ni substrates as the singlebuffer layer for HTS coated conductors by using high-rate photo-assisted metal–organicchemical vapour deposition (PhAMOCVD) at a relatively low deposition temperature of600 °C. YBCO superconducting films were then successfully deposited on these thick SCO singlebuffer layers by the same high-rate PhAMOCVD process, and yielded critical current densities(Jc)of ∼0.52 MA cm−2 at 77 K and zero applied field. X-ray diffraction and scanning electron microscopeanalyses of SCO/Ni samples revealed very good crystalline structure and surfacemorphology for the SCO single buffer layers. These results suggest that SCOsingle buffer layer, as well as the YBCO conductors, fabricated by the high-ratePhAMOCVD technique may offer great potential for manufacturing YBCO coatedconductors.

Characterization of low temperature photo-assisted metal-organic chemical vapor deposited copper films using hexafluoroacetylacetonate copper(I) trimethylvinylsilane as precursor

This work demonstrated for the first time low temperature copper (Cu) film deposition by photo-assisted metal-organic chemical vapor deposition (photo-assisted MOCVD) using hexafluoroacetylacetonate copper(I) trimethylvinylsilane (referred to as Cu(hfac)(tmvs)) as precursor. This work found that photo-assisted MOCVD Cu films can be deposited on TaN/tetra-ethylorthosilicate(TEOS)-oxide/Si but not on TEOS-oxide/Si wafers at temperatures as low as 100 °C. Cu films grown by photo-assisted MOCVD from Cu(hfac)(tmvs) at 125 °C exhibit good qualities, including acceptable electromigration lifetime, lower carbon contamination at the Cu film surface, and excellent step-coverage and trench-filling abilities.

Photo-assisted MOCVD of copper using Cu(hfa)(COD) as precursor

Cu thin films were deposited in the temperature range 100–180°C using the title precursor by photo-MOCVD. The ultraviolet (UV) photons facilitate a clean removal of the ligands. Consequently, the growth rate is slightly increased under irradiation and the morphology and the film resistivity is improved.

Coated conductor development by photo-assisted MOICVD growth of YBCO thick films and buffer layers

YBa 2Cu 3O 7−x films have been deposited by photo-assisted MOCVD at commercially viable rates on both single crystal oxide substrates and atomically textured metallic substrates. CeO 2 and YSZ buffer layers have also been developed by photo-assisted MOCVD for deposition on metallic substrates at rates approaching 1 μm/min. The resulting buffer layers show good duplicate of the moderate order of the underlying metallic substrates, and the subsequent YBCO layers show similar moderate atomic order with resulting J c ∼ 5 × 10 5 A/cm 2.

Development of High Critical Current YBCO Coated Conductors By Photo-Assisted MOCVD

ABSTRACTYBa2Cu3O7 (YBCO) films have been deposited by photo-assisted MOCVD at rates of greater than 0.3μm/min on both single crystal oxide substrates and atomically textured metallic substrates. The YBCO films of thickness from 0.5μm to 3μm deposited on LaAlO3 substrates are shown to be highly atomically ordered with Jc> 1 × 106 A/cm2. CeO2 buffer layers have also been developed by photo-assisted MOCVD for the integration of YBCO with metallic substrates. The CeO2 layers were found to be crack-free when grown on nickel even above 1 micron thickness, and exhibited crystal orientation and in-plane alignment similar to that of the atomically textured Ni substrates. YBCO films grown on the thick CeO2 buffer layers on nickel substrates have shown promising results with Jc∼6 × 105 A/cm2.

Low Pressure Photo-Assisted Mocvd for the Production of Homogeneous, Low-Strain, Amorphous Titanium Oxide Films

AbstractThin films of titania have been grown by photo-assisted MOCVD which are amorphous and relatively strain free, with high refractive index, low optical loss and structural features all less than 100 nm in size. The stoichiometry is very close to TiO2 and the impurity content is negligible except for a small amount of calcium, thought to have been leached from the glass substrate. The optimum deposition conditions were found to involve a deposition temperature of around 200 °C, a cell pressure of 5.6 torr and the introduction of nitrous oxide, decomposed by UV irradiation to give oxygen free radicals which acted as an oxidant.

GaNP growth by photo-assisted MOCVD and its optical characterization

GaNP growth by photo-assisted MOCVD and its optical characterization

Surface Catalyzed Photo-Assisted Mocvd of Cobalt Thin Films for Enhanced Control of Magnetic Properties

AbstractThin films of cobalt have been deposited by photo-assisted metal-organic chemical vapour deposition. Samples of thickness less than 60 nm, grown at 110 °C, exhibit inverse hysteresis when an external magnetic field is applied in a particular direction normal to the plane of the film. These films are a mixture of crystalline and, possibly, amorphous phases with a grain size of about 130 nm and a significant oxygen content throughout. The potential roles of the various physical characteristics, as well as that of the photolytic deposition process itself, in the origin of the inverse hysteresis are discussed, as is a possible self-limiting growth mechanism.

The growth of ZnSe by photo-assisted metalorganic chemical vapor deposition (MOCVD)

ZnSe epitaxy layers were grown on (1 0 0)GaAs substrates by photo-assisted MOCVD using DMZn and DMSe as group II and VI sources, respectively. Irradiation can improve the growth rate efficiently, but the irradiation intensity influences the growth rate and the crystalline quality negligibly in a large range. Due to an oxidation reaction on the surface of ZnSe, the growth rate and the flow ratio of group II and VI sources influence the crystalline quality.

Photo-Assisted MOCVD Fabrication of YBCO Thick Films and Buffer Layers on Flexible Metal Substrates for Wire Applications

Photo-assisted MOCVD has been developed for application to high-rate, high quality YBa2Cu3O 7-δ thin film production. This technique is now being applied to the fabrication of thick film YBa2Cu3O 7-δ on flexible metal substrates for wires and tapes. The unique application of photo-irradiation as the sole source of energy for the MOCVD reaction has resulted in extremely rapid growth rates for YBCO films with accompanying high superconducting performance. Typical YBCO films of thickness >1 μ m exhibit J c ≥ 1 × 106 A/cm2 and T c > 90 K on single crystal oxide substrates. Such films have now been integrated to metal substrates such as single crystal Ni(100) and roll-textured nickel foil. YBCO films grown on textured Ni foils with CeO2 and YSZ buffer layers show J c ≈ 3 to 5 × 105 A/cm2 for films of 1 μ m thickness grown in 2 to 4 minutes time. Such performance for thick films made in such short growth time is promising for YBCO wire fabrication. The development of effective YBCO wire through thick film growth on flexible substrates also requires buffer layer application. Photo-assisted MOCVD has also been applied to buffer layer formation with promising results.

Blue-green laser diode grown by photo-assisted MOCVD

Operation of the first blue-green laser diode grown by metalorganic chemical vapor deposition has been demonstrated at 77 K under pulsed current injection. The precursors were dimethylzinc, dimethylcadmium, diethylsulfide, bismethyl-cyclopentadienyl-magnesium, and dimethylselenide. Diisopropylamine and ethyliodide were used for a p-type and n-type doping under irradiation with ultraviolet light generated by a high-pressure mercury lamp, respectively. A 1 × 10 18 cm −3 nitrogen-atom concentration, which was measured by secondary ion mass spectroscopy, was obtained in the p-ZnSe contact layer. The 4.2 K photoluminescence spectrum was dominated by strong donor-acceptor pair emission and the net acceptor concentration was 1.4 × 10 16 cm −3 .