Photo-assisted Metal Organic Chemical Vapor Research Articles

Electrically pumped green lasing action from InGaN/GaN MQW heterojunction with a p-NiO cap layer

Electrically pumped green lasing action has been achieved from an In0.23Ga0.77N/GaN multi quantum well heterojunction with a p-NiO cap layer. The NiO epilayer grown by photo-assisted metal organic chemical vapor deposition (MOCVD) showed high crystal quality with cubic NaCl morphological structure. Under forward bias, distinct diode rectification characteristics were obtained and the turn-on voltage was about 2.0 V. Increasing the current to 30 mA, strong sharp lasing peaks with narrower line width of 0.8 nm was detected. The lasing mechanism and current transport of the diode were studied through the aspects of energy band structure of the diode.

Characteristics of doping controllable ZnO films grown by photo-assisted metal organic chemical vapor deposition

Arsenic doped p-type ZnO films are prepared by the photo-assisted metal organic chemical vapor deposition method. Using the photo-assisted technique, the acceptor activation process is simplified. The arsenic doping level, which decides the carrier distribution, could be controlled by changing the thickness of the pre-deposited GaAs layer. The crystal and optical quality of the ZnO films is good. The acceptor is AsZn–2VZn. Its ionization energy could be slightly reduced by increasing the arsenic doping level. This finding is very helpful to improve the hole concentration. Our experiments provide a new method to grow high performance p-type ZnO based photoelectric devices.

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.

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.

Crystalline, Optical and Electrical Properties of NiZnO Thin Films Fabricated by MOCVD

NiZnO thin films are grown on c-plane sapphire substrates by using a photo-assisted metal organic chemical vapor deposition (MOCVD) system. The effect of the Ni content on the crystalline, optical and electrical properties of the films are researched in detail. The NiZnO films could retain a basic wurtzite structure when the Ni content is less than 0.18. As Ni content increases, crystal quality degradation could be observed in the x-ray diffraction patterns and a clear red shift of the absorption edge can be observed in the transmittance spectrum. Furthermore, the donor defects in the NiZnO film can be compensated for effectively by increasing the Ni content. The change of Ni content has an important effect on the properties of NiZnO films.

Improvement in the Property of Field Effect Transistor Having the HfO2/Ge Structure Fabricated by Photoassisted Metal Organic Chemical Vapor Deposition with Fluorine Treatment

We have fabricated Ge-based p-channel metal–insulator–semiconductor field effect transistor (p-MISFET) devices using a hafnium oxide (HfO2) gate film prepared by photoassisted metal organic chemical vapor deposition (MOCVD). To reduce the interface state of a HfO2/Ge gate stack, we performed a new F2 treatment method on a Ge surface. Before the deposition of HfO2 insulation thin films on n-type Ge(100), Ge surfaces were treated in fluorine (F2) gas ambient under various conditions. Experimental results show that F is densely distributed at the interface of the HfO2/Ge gate stack with the F2 treatment of the HfO2 bottom layers. Poorly passivated dangling bonds and oxygen vacancies (Vo) near the interface between HfO2 and Ge were stabilized by chemically active F. Consequently, the interface state density (Dit) of the HfO2/Ge gate stack was reduced and the electrical characteristics of the HfO2/Ge p-MISFETs were improved. Therefore, the new F2 treatment method is very useful for fabricating a good HfO2/Ge p-MISFET device.

Improvement in the Property of Field Effect Transistor Having the HfO2/Ge Structure Fabricated by Photoassisted Metal Organic Chemical Vapor Deposition with Fluorine Treatment

We have fabricated Ge-based p-channel metal–insulator–semiconductor field effect transistor (p-MISFET) devices using a hafnium oxide (HfO2) gate film prepared by photoassisted metal organic chemical vapor deposition (MOCVD). To reduce the interface state of a HfO2/Ge gate stack, we performed a new F2 treatment method on a Ge surface. Before the deposition of HfO2 insulation thin films on n-type Ge(100), Ge surfaces were treated in fluorine (F2) gas ambient under various conditions. Experimental results show that F is densely distributed at the interface of the HfO2/Ge gate stack with the F2 treatment of the HfO2 bottom layers. Poorly passivated dangling bonds and oxygen vacancies (Vo) near the interface between HfO2 and Ge were stabilized by chemically active F. Consequently, the interface state density (Dit) of the HfO2/Ge gate stack was reduced and the electrical characteristics of the HfO2/Ge p-MISFETs were improved. Therefore, the new F2 treatment method is very useful for fabricating a good HfO2/Ge p-MISFET device.

PREPARATION AND CHARACTERIZATION OF HAFNIUM SILICATE DIELECTRIC LAYERS BY PHOTO-ASSISTED MOCVD USING MIXED PRECURSOR OF Hf(O-t-C4H9)4 AND Si(O-t-C4H9)4

ABSTRACT Hafnium silicate dielectric layers have been prepared by photo-assisted metal organic chemical vapor deposition (MOCVD) using mixed precursor of Hf(O-t-C4H9)4 and Si(O-t-C4H9)4. Deuterium lamp was used for ultraviolet irradiation source to enhance decomposition of mixed precursor. It was confirmed from X-ray photoelectron spectroscopy (XPS) measurement that hafnium silicate dielectric layers were deposited successfully. The hafnium silicate dielectric layers exhibited improved surface roughness (0.12∼ 0.17 nm) and thermal stability. Electrical characterizations revealed that accumulated capacitance, leakage current and interface trap state density were improved, and these improvements may be caused from effective decomposition of mixed precursor by ultraviolet irradiation.

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.