Photo-assisted Metal Organic Chemical Vapor Deposition Research Articles

High hole concentration Li-doped NiZnO thin films grown by photo-assisted metal–organic chemical vapor deposition

High hole concentration Li-doped NiZnO thin films were grown by metal–organic chemical vapor deposition (MOCVD). The crystalline, optical, electrical, and morphological characteristics of the NiZnO films were studied as a function of lithium content. The resistance of the films decreased and the hole concentration greatly increased with increasing lithium content. However, the crystalline and optical properties were observed to degrade as the lithium content was increased. To relieve the degradation, a photo-assisted MOCVD method was used in order to restrict this degradation and this represents a new way to obtain stable high hole concentration NiZnO films.

Improved ultraviolet emission performance from polarization-engineered n-ZnO/p-GaN heterojunction diode

O-polar ZnO films were grown on N-polar p-GaN/sapphire substrates by photo-assisted metal-organic chemical vapor deposition, and further heterojunction light-emitting diodes based O-polar n-ZnO/N-polar p-GaN were proposed and fabricated. It is experimentally demonstrated that the interface polarization of O-polar n-ZnO/N-polar p-GaN heterojunction can shift the location of the depletion region from the interface deep into the ZnO side. When a forward bias is applied to the proposed diode, a strong and high-purity ultraviolet emission located at 385 nm can be observed. Compared with conventional Zn-polar n-ZnO/Ga-polar p-GaN heterostructure diode, the ultraviolet emission intensity of the proposed heterojunction diode is greatly enhanced due to the presence of polarization-induced inversion layer at the ZnO side of the heterojunction interface. This work provides an innovative path for the design and development of ZnO-based ultraviolet diode.

Nanodots and microwires of ZrO2 grown on LaAlO3 by photo-assisted metal–organic chemical vapor deposition**Project supported by the National Natural Science Foundation of China (Grant No. 51002063) and the International Science and Technology Cooperation Program of Science and Technology Bureau of Changchun City, China (Grant No. 12ZX68).

ZrO2 nanodots are successfully prepared on LaAlO3 (LAO) (100) substrates by photo-assisted metal-organic chemical vapor deposition (MOCVD). It is indicated that the sizes and densities of ZrO2 nanodots are controllable by modulating the growth temperature, oxygen partial pressure, and growth time. Meanwhile, the microwires are observed on the surfaces of substrates. It is found that there is an obvious competitive relationship between the nanodots and the microwires. In a growth temperature range from 500 °C to 660 °C, the microwires turn longest and widest at 600 °C, but in contrast, the nanodots grow into the smallest diameter at 600 °C. This phenomenon could be illustrated by the energy barrier, decomposition rate of Zr(tmhd)4, and mobility of atoms. In addition, growth time or oxygen partial pressure also affects the competitive relationship between the nanodots and the microwires. With increasing oxygen partial pressure from 451 Pa to 752 Pa, the microwires gradually grow larger while the nanodots become smaller. To further achieve the controllable growth, the coarsening effect of ZrO2 is modified by varying the growth time, and the experimental results show that the coarsening effect of microwires is higher than that of nanodots by increasing the growth time to quickly minimize ZrO2 energy density.

Nickel flux induced effects on structural and optical properties of NiO films fabricated by PA-MOCVD

In the present work, we report the growth of NiO films fabricated by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD). The growth parameter of nickel flux affects the crystallographic, morphological and optical properties of NiO films, which were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible spectrophotometer (UV). It is found that the NiO grains were increased with increase in nickel flux from an anomalous state to a cubic shape following the NaCl-type structure. The NiO films presented highly c-axis preferred orientation with significant (111) diffraction. The samples marked A-E under the nickel flux of 2, 4, 6, 8 and 10 sccm respectively have optical band gap values of 3.55 eV, 3.71 eV, 3.82 eV, 3.91 eV and 3.95 eV, respectively. Comparatively, the controllable electrical properties of NiO epilayers can be achieved by the variations of crystal quality arise from the nickel flux.

Fabrication of GdBa2Cu3O7−δ films by photo-assisted-MOCVD process

Pure GdBa2Cu3O7−δ (GdBCO) films were deposited on (100)-oriented LaAlO3 (LAO) substrates by photo-assisted metal organic chemical vapor deposition (PhA-MOCVD) technique. The effects of substrate temperature (Ts) and oxygen partial pressure (Po2) on microstructure, growth rate and superconducting critical current density (Jc) were investigated. A dense and no grain boundary visible, single-crystal-like cross-sectional morphology was observed. For the GdBCO film sample obtained at Ts of 810°C and Po2 of 4Torr, the full width at half-maximum were 0.08° and 0.41° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single crystal GdBCO. Optimally processed GdBCO samples exhibited Jc of 2.5 MA/cm2 at 77K in self-field. A relatively high growth rate of 0.104μm/min for the GdBCO film is realized by the PhA-MOCVD technique.

Preparation of ZnS thin films by using photoassisted MOCVD

Zinc sulfide thin films were grown by using both normal metal-organic chemical vapor deposition (MOCVD) and photoassisted MOCVD with diethylzinc and t-butylthiol as sources for the zinc and the sulfur, respectively. The effects of UV irradiation and reactor chamber pressure on the film growth were investigated. The basic physical properties of the ZnS thin films grown by using MOCVD were also investigated with X-ray diffraction, optical absorption, and Raman spectroscopy. The growth rate of the ZnS thin films grown by using photoassisted MOCVD were improved by about 28% compared to that of the films grown by using normal MOCVD. The growth rate also increased with increasing reactor chamber pressure. The energy band gap obtained from the optical absorption spectrum was 3.58 eV. MOCVD-grown ZnS thin films were hexagonal (lattice constants: a = 0.382 nm and c = 0.626 nm). In the Raman spectrum, the A1 and the E1 transverse peaks (A1(TO) and E1(TO)) were observed at 277 cm−1, and the A1 and the E1 longitudinal peaks (A1(LO) and E1(LO)) were observed at 354 cm−1.

Deposition and characterization of nanostructured Cu2O thin-film for potential photovoltaic applications

Abstract

Photo-assisted metal-organic chemical vapor deposition of CaCu3Ti4O12 (CCTO) thin films

Calcium copper titanate (CaCu3Ti4O12) or CCTO is one of the most researched giant dielectric constant materials in recent years. In the present work, incoherent light source based photo-assisted metal-organic chemical vapor deposition (MOCVD) has been used to prepare CCTO thin films on Si/SiO2 substrates. Key to this unique processing technique is the use of UV radiation as an additional source of energy in conjunction to the thermal energy. The given Photo-assisted MOCVD processing resulted in polycrystalline CCTO growth on a SiO2 surface. Powder X-ray diffraction and scanning electron microscopy were performed to analyze structural and compositional properties of the CCTO thin film. Ellipsometric measurements indicated a refractive index of 3.03 for the CCTO thin film.

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.

Photofacilitated Controllable Growth of ZnO Films Using Photoassisted Metal Organic Chemical Vapor Deposition

High-quality ZnO thin films were deposited on sapphire substrates using a photoassisted metal–organic chemical vapor deposition (PA-MOCVD) system. A controllable morphology evolution with varying d...

Effect of growth temperature on structure and optical characters of NiO films fabricated by PA-MOCVD

We report the effect of growth temperature on structure, optical and electrical properties of NiO films fabricated by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD). It is found that the crystal quality of the NiO films has been improved by increasing the growth temperature. When the temperature is low, the NiO film is composed of small and anomalous grains, whereas the film is composed of grains with a cubic shape following the NaCl-type structure when the temperature is higher. The samples marked A–D under the growth temperature of 510, 540, 570 and 600 °C have optical band gap values of 3.93 eV, 3.82 eV, 3.73 eV and 3.55 eV, respectively. Comparatively, the controllable electrical properties of the films can be achieved by the variation of crystal quality arises from the growth temperature.

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.

Improvement in the Electrical Characteristics of a Fluorinated HfO2/Ge Gate Stack by Using a Nitrogen Radical Treatment

The electrical property of the interfacial layer is improved by fluorine treatment on a HfO2/Ge metal-insulator-semiconductor (MIS) device. The thin HfO2 dielectric was prepared using a photoassisted metal-organic chemical vapor deposition (MOCVD) system. However, the fluorine was easily out-diffused after post metallization annealing (PMA) at high temperature. In this study, the post nitridation of the fluorinated HfO2/Ge gate stack was carried out by using a nitrogen (N) radical treatment at high temperature (200 ◦C) to prevent the fluorine (F) diffusion. Interface traps, such as poorly passivated dangling bonds and oxygen vacancies (V0), near the interface were passivated by co-doping of F and N. Consequently, the dielectric property of the HfO2/Ge gate stack was improved to hamper F out-diffusion. Therefore, we suggest that N radical treatment following F2-treatment is a very useful solution for improving the dielectric property of a HfO2/Ge gate stack.

The effect of susceptor inclination angle on the quality of superconducting YBCO thin films prepared by a photo-assisted MOCVD system

Superconducting YBa2Cu3O7−x thin films were deposited on LaAlO3 (100) substrates by a photo-assisted metal-organic chemical vapor deposition (MOCVD) technique. In our experiment, growth temperature, chamber pressure and growth time were all fixed; the only process variable was the susceptor inclination angle (Φ) between the axis of gas inlet and the susceptor surface. It was found that the growth rate of YBCO films increases monotonically as Φ increases, whereas the superconducting critical current density (Jc) has a maximum (1.2×106A/cm2) near Φ=22.5°. The experimental results were found to be well correlated with the three-dimensional simulations of gas flow inside the MOCVD reactor, with Φ being the only process variable.

ESR studies of hydrogen-induced paramagnetic defects in polycrystalline ZnO films

The hydrogen doping effect was investigated in polycrystalline ZnO and ZnO:H thin films prepared by the photoassisted metalorganic chemical vapor deposition (photo-MOCVD) technique. In situ post-deposition hydrogen doping was provided using mercury sensitized photodecomposition of hydrogen gas. The structure and morphology of the films were monitored by XRD and FTIR measurements. The studies of paramagnetic defects in as-grown and hydrogenated ZnO thin films were undertaken in the temperature range 77–300K using X-band ESR spectrometer. It was found that all the samples exhibit a single strong Lorentzian line at g=1.956. The line intensity was shown to increase upon H-doping. The concentration of paramagnetic defects in the samples, associated with shallow donors, was found to be 8.2×1017cm−3 for as-grown ZnO and 1.9×1018cm−3 for hydrogen treated ZnO:H thin films. The nature of broadening of ESR line in polycrystalline ZnO thin films due to the surface effects is discussed.

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.

Improvement of electrical stability of polycrystalline ZnO thin films via intentional post-deposition hydrogen doping

We investigate the hydrogen doping effect on polycrystalline ZnO thin films prepared by the photoassisted metalorganic chemical vapor deposition technique. In situ post-deposition hydrogen doping was performed using mercury-sensitized photodecomposition of hydrogen gas. From Fourier transform infrared spectra, we observe small changes in O–H bond-stretching local vibrational modes as a result of hydrogen doping. The photoluminescence measurements reveal that intentional hydrogen doping significantly suppresses nonradiative recombination centers in the ZnO films. The undoped ZnO film reveals a heavily n-type as-grown conductivity due to the high hydrogen content, but it is unstable in a humid air atmosphere. However, the electrical stability is significantly improved as a result of hydrogen doping.

Preparation and characterization of HfO2thin films by photo-assisted MOCVD

High-k dielectric HfO 2 thin films have been prepared by photo-assisted metal-organic chemical vapor deposition (MOCVD). Vacuum ultraviolet (VUV) light is used for enhancement of chemical reaction of the source materials of (Hf(O-t-C 4 H 9 ) 4 ) (HTB) and H 2 O. The absorption spectrum of HTB has been calculated with molecular orbital method. The calculated infrared absorption of HTB is found in VUV region (around 150nm), and HfO 2 thin films were deposited under the irradiation with VUV light of a D 2 lamp including the HTB absorption band. These prepared films are characterized by FT-IR measurement to estimate the concentration of organic impurities. It shows that C-H peak drastically decreases less in the photo-assisted MOCVD film than the MOCVD. Moreover, C-V characteristics show that accumulation capacitance is increased in the film deposited under VUV irradiation. The accumulation capacitance is much increased by rapid thermal annealing (RTA) in the case of photo-assisted MOCVD. AFM observation results show that very smooth surface is obtained in the photo-assisted MOCVD films.

YBa2CU3O7-x THICK FILMS DEPOSITED BY PHOTO-ASSISTED METAL-ORGANIC CHEMICAL VAPOR DEPOSITION

High-quality YBa2Cu3O7-x ( YBCO ) thick films with thickness over 4.0μm were deposited by photo-assisted metal-organic chemical vapor deposition (PhA-MOCVD) technique with high growth rates. Microstructures of YBCO thick films have been systematically investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction techniques. The fabricated YBCO thick films are very dense and single-crystal like with no visible grain boundaries or voids. The high quality of the prepared YBCO thick films was confirmed further by the results of X-ray diffraction analyses and Jc measurements. Thus, these thick YBCO films prepared by PhA-MOCVD technique have promising application potential in fields such as coated conductors.