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High excitonic binding energy of pristine (LaO)MnAs and change from antiferromagnetic into ferrimagnetic due to F doping.

We report the growth of non-polar GaN and AlGaN films on Si(111) substrates by plasma-assisted metal-organic chemical vapor deposition (PA-MOCVD). Low-temperature growth of GaN or AlN was used as a buffer layer to overcome the lattice mismatch and thermal expansion coefficient between GaN and Si(111) and GaN’s poor wetting on Si(111). As grown, the buffer layer is amorphous, and it crystalizes during annealing to the growth temperature and then serves as a template for the growth of GaN or AlGaN. We used scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) characterization to investigate the influence of the buffer layer on crystal structure, orientation, and the morphology of GaN. We found that the GaN buffer layer is superior to the AlN buffer layer. The thickness of the GaN buffer layer played a critical role in the crystal quality and plane orientation and in reducing the cracks during the growth of GaN/Si(111) layers. The optimum GaN buffer layer thickness is around 50 nm, and by using the optimized GaN buffer layer, we investigated the growth of AlGaN with varying Al compositions. The morphology of the AlGaN films is flat and homogenous, with less than 1 nm surface roughness, and has preferred orientation in a-axis.

The deposition of InGaN thin films by plasma-assisted metalorganic chemical vapor deposition is achieved using nitrogen plasma as a nitrogen source. The generation of nitrogen plasma is optimized using optical emission spectroscopy, and the plasma is dominated by excited molecular nitrogen, which emits in the range 300–420 nm. The emission intensity of the plasma significantly depends on the flow rate of nitrogen gas and heater temperature and are optimally 70 SCCM and 650 °C, respectively. A further increase in these parameters results in a decrease in the intensity of the nitrogen plasma emission. An optimal flow rate and heater temperature are used to grow InGaN thin films on c-sapphire substrates. InGaN thin films grown with a TMIn vapor concentration (xv) of 0%, 50%, and 100% at a growth temperature of 650 °C are highly oriented to the (0002) plane in a hexagonal structure. The film grown with a vapor concentration of 50% has an indium concentration of 55% and no indication of phase separation. Increasing the growth temperature above 650 °C results in a decrease in the growth rate.

TiO2 thin films were deposited on silicon substrates by metalorganic chemical vapor deposition (MOCVD). The deposited films were characterized using scanning electron microscopy (SEM) and X‐ray diffraction (XRD). We investigated TiO2 thin films growth parameters in relation to the film's physical properties. The growth temperature is the most important growth parameter that influences crystal orientation, grain size and surface morphology of the grown TiO2 thin films. The TiO2 films were utilized as hydrogen gas sensing layer and we characterized their response on the expose to hydrogen gas. We measured hydrogen gas sensing properties and analyzed them by correlating the film's physical properties with the gas sensing properties. Hydrogen gas sensor utilizing TiO2 thin films are able to detect hydrogen gas at concentration of 1000–10 000 ppm with high response. It is found that smaller the grain size and thinner the film thickness give higher sensor response as well as faster response and recovery time.

Co:TiO2 (cobalt-doped titanium dioxide) thin films have been deposited on the n-type Si (100) substrate at the temperatures range of 325°C 450°C using MOCVD (metal organic chemical vapor deposition) technique. We investigated the effect of growth temperature on the structural and morphological quality of Co:TiO2 thin films. The structure of Co:TiO2 thin films were characterized by XRD while the morphology and the thickness of films were characterized by SEM. The XRD results reveal that all films show the anatase structure and the dominant orientation of anatase phase depends on the growth temperature. The grain size of crystal increases as the growth temperature increases. We also reveal that the growth rate of Co:TiO2 film has a maximum value at the growth temperature of 400°C.

Dye-sensitized solar cell (DSSC) which employed natural dye from black rice has been successfully fabricated and improved its performance by depositing interconnected copper (copper bridge) on the space between TiO2. The copper bridge has significant role in minimizing recombination of electron-hole which occurred in TiO2 surface by trapping electron and facilitating to anode. The presence of interconnected copper nanoparticle in the space between TiO2 nanoparticle was confirmed by Scanning Electron Microscopy (SEM) and X-Ray Diffractometer (XRD). The current-voltage (I-V) characterization of DSSC solar cells by using Keithley 617 was also performed to investigate performance of solar cells under sun illumination in varying intensities. It is found that performance of copper coated DSSC solar cells (efficiency 0.35% and fill factor 0.35) is higher than DSSC without copper coating (efficiency 0.17% and fill factor 0.35). This result is consistent with impedance spectroscopy analyzing where the internal resistance of copper coated DSSC solar cells is lower than DSSC without coated. It is concluded that performance of DSSC increasing with decreasing of internal resistance. Our finding is higher than other researcher reports in Ref. [13] and [14] with similar structure and kind of natural dye. In addition, this paper also reports the use of polymer electrolyte which employing polyvinyl acetate (PVA) containing lithium ion to maintain long-term stability of device.

Dimethyltelluride has been used as a dopant source for GaSb epilayers grown via atmospheric pressure metalorganic chemical vapour deposition (MOCVD). It has been observed that the electron concentration (n) is proportional to the Te partial pressure in the vapour phase, until n saturates at high Te partial pressure. Electron concentrations as high as 1.36 × 1018 cm– 3 have been measured with imperfect morphology, and as high as 1.22 × 1018 cm– 3 with excellent, mirror like, morphology. These appear to be the highest electron concentrations reported to date for any MOCVD-growth epitaxial n-type GaSb doped with DMTe and grown at 540 °C with a V/III ratio of 1.4. The absorption spectra of GaSb doped with DMTe show that the heavily doped samples have a less abrupt edge. The absorption coefficient (α) strongly depends on the free carrier concentration. PL spectra of the epilayers are also reported.

Different approaches have been made in order to reach higher solar cells efficiencies. Concepts for multilayer solar cells have been developed. This can be realised if multiple individual single junction solar cells with different suitably chosen band gaps are connected in series in multi-junction solar cells. In our work, we have simulated and optimized solar cells based on the system mechanically stacked using computer simulation and predict their maximum performance. The structures of solar cells are based on the single junction GaAs, GaAs0.5Sb0.5 and GaSb cells. We have simulated each cell individually and extracted their optimal parameters (layer thickness, carrier concentration, the recombination velocity, etc), also, we calculated the efficiency of each cells optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The optimal values of conversion efficiency have obtained for the three individual solar cells and the GaAs/GaAs0.5Sb0.5/GaSb tandem solar cells, that are: η = 19,76% for GaAs solar cell, η = 8,42% for GaAs0,5Sb0,5 solar cell, η = 4, 84% for GaSb solar cell and η = 33,02% for GaAs/GaAs0.5Sb0.5/GaSb tandem solar cell.

A comparative study of the structural and electrical properties of GaN films grown by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) at 700°C, with and without AlN buffer layer is presented . Hydrogen plasma was used in addition to nitrogen plasma to produce GaN. The introduction of H-plasma is found to influence the properties of the films. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and Hall Effect measurements show that the sample with AlN buffer layer possesses a smoother and more homogenous morphological characteristics as well as a lower background electron and higher Hall mobility as compared to the sample without buffer layer. X-ray diffraction (XRD) reveals that hydrogenation is capable of producing the epitaxial GaN films at reduced temperatures with the full width at half maximum (FWHM) of the x-ray rocking (XRC) of GaN (0002) reflection was found to be 54.8 and 256 arcmin for samples with buffer layer and without buffer layer, respectively.

We report on the characteristics of metal-semiconductor-metal (MSM) photodiodes based on GaN films grown on silicon substrates by electron cyclotron resonance (ECR) plasma-assisted metalorganic chemical vapor deposition (PA-MOCVD) at growth temperature of 200 and 600 °C. Structural analysis of the GaN samples used for the photodiodes fabrication were performed by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) to analyze the crystalline quality of the samples. The analysis has revealed that the GaN samples grown at 200 and 600 °C were in amorphous and microcrystalline phase, respectively. Electrical characterization of the MSM photodiodes were carried out by using current–voltage ( I – V ) measurements. At 10 V, the photodiodes based on amorphous GaN has a dark current of 0.18 μA while the microcrystalline GaN based photodiode has a dark current of 18 μA.

Thin films of lead zirconium titanate [PbZr0.525Ti0.475O3 (PZT)] and 1% tantalum-oxide-doped lead zirconium titanate [Pb0.9950(Zr0.525Ti0.465Ta0.010)O3 (PTZT)] deposited on Pt(200)/SiO2/Si(100) using the dc unbalanced magnetron sputtering (DC-UBMS) method have been investigated. The films were grown at deposition temperatures in the range of 300 °C to 750 °C for 3 hours, followed by annealing at 700 °C for 1 hour for each deposited film. Observations by X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the physical and pyroelectric properties of the grown films. The films show tetragonal structure with preferred orientation to the (100) and (200) crystal planes. The calculated lattice constants are: a = b = 4.056 A, c = 4.105 A for PZT thin film; and a = b = 4.056 A, c = 4. 068 A for PTZT thin film. The physical properties extracted from the I–V curves show that the PZT and PTZT films are insulator or dielectric materials. The conductivity (σ) of PZT films is between 2.24 × 10−13 (Ω m)−1 and 5.00 × 10−12 (Ω m)−1, whereas the conductivity (σ) of PTZT films is between 1.02 × 10−9 (Ω m)−1 and 1.90 × 10−8 (Ω m)−1 for films deposited at the temperature ranges mentioned. The voltage responsivity (rv) measured at chopper frequency of 2000 Hz and at wavelength of 947 nm is 62.1–80 μV/W and 61–76.4 μV/W for PZT and PTZT thin films, respectively. Meanwhile, the pyroelectric coefficient (p) is in the range of 9.54 × 10−4 to 12.3 × 10−4 C/m2 K for PZT thin films and 9.35 × 10−4 to 11.7 × 10−4 C/m2 K for PTZT thin films. These results show that PZT and PTZT thin films are suitable for use as a pyroelectric infrared sensor. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thin films of YBCO have been grown by a home-built-MOCVD vertical reactor. The growth temperature were varied between 600 and 750 °C and the growth rates were 0.4–0.5 μm/h. At the substrate temperature between 630 and 675 °C, the films consist of a mixture of a-axis and c-axis oriented grains, while at temperature of 700 °C or higher, the a-axis oriented grain changed to random orientation. The stoichiometric composition of Y:Ba:Cu for films grown at 680 °C or higher is almost 1:2:3, as confirmed by electron dispersive X-rays (EDAX) spectra. Films deposited at 680 and 700 °C show superconducting critical temperature around 87 and 87.4 K, respectively. Films properties are comparable with film grown using horizontal MOCVD reactor reported by previous reports.

We report the fabrication of a dye-sensitized solar cell (DSSC) using low-cost materials (carbon ink from an inkjet printer coated on glass as the counter electrode) and made by a combination of spray deposition and doctor blade methods. We noted that the efficiency of the DSSC with the carbon-coated electrode (1.13%) was comparable to that with a platinum-coated counter electrode (1.16%). We also proposed an equivalent circuit for this solar cell. The value of the charge-transfer resistance was determined both experimentally and analytically, and we found that both approaches produced the same results. Moreover, we improved the efficiency of DSSC based carbon by depositing copper nanoparticle into the space between Titanium Dioxide (TiOv2) nanoparticle using electroplating methods.

The effect of a flow guide in a vertical MOCVD reactor on the deposition uniformity and growth rate of thin YBCO films has been studied. Without the flow guide the growth rates are low, have a poor uniformity and the film composition is not stoichiometric. The growth rate of the films grown using a reactor with the flow guide was approximately twice that without the flow guide. Using this flow guide the growth rates were 0.4-0.7 μm/h for growth temperatures varying between 600 and 750 °C, and the crystalline quality as well as the surface morphology of YBCO films on MgO substrates is improved. For films grown at temperatures above 650 °C the composition of Y:Ba:Cu is 1:2:3, as confirmed by EDAX spectra. Films deposited without and with the flow guide at 700°C have critical temperatures around 85 and 88 K, respectively. The reduction in ΔT c (T c,zero -T c,onset ) also shows an improvement of the superconducting properties of YBCO thin films deposited with a flow guide.

GaN films have been grown on a-plane (1 1 2 0) sapphire substrates by plasma-assisted MOCVD using TMGa (trimethylgallium) and plasma-cracked N2. The crystallinity, electronic properties and optical absorption of films were characterized by X-ray diffraction, Hall-van der Pauw measurement method and UV-vis spectrometry, respectively. It was found that GaN films grown at 600°C have a wurtzite structure with (0 0 0 1) orientation and films grown at 640°C have a mixture of crystallites with phase dominant peaks of (1 0 1 0) . The carrier density of GaN film grown at 600°C is n=5×1019 cm−3 and its bandgap is 3.4 eV. As the N2 flow rate increases, the carrier densities decrease to n=1.7×1019 cm−3 and the mobility increases.

We report results of electrical characterisation of MIS diode structures with Al metallisation, an insulating layer of low temperature grown (LT) GaAs on a n+ GaAs substrate. The I–V characteristics at varying temperatures between 120 K and 285 K and a.c. conductivity measurements between 1 kHz and 13 MHz at room temperature were examined. The I–V characteristics were analyzed through the dependence of the diode ideality factor on temperature. Values between 2.8 and 4 were obtained, typical of tunneling through the depletion potential barrier in the n+ GaAs at the interface. The high voltage part of the forward I–V characteristics indicates a low and weakly temperature dependent series resistance of the diode, associated with carrier transport through LT-GaAs, characterised by an activation energy of 32 meV. The a.c. dynamic resistance in the high voltage part of the I–V characteristics decreases as a function of frequency and between 2 MHz and 13 MHz approximately follows ωs dependence with s = 0.65. These results are consistently interpreted as the result of the transport of injected carriers through the LT GaAs layer via a hopping mechanism involving defects.

We investigated theoretically the electron mobility in low temperature grown GaAs (LT GaAs), based on the ‘internal Schottky barrier’ model, utilizing a Monte Carlo method. We used a novel approach to overcome the problem of inhomogeneity of the internal electric field due to the presence of precipitates. The behaviour of mobility as a function of temperature in LT GaAs for precipitate concentrations in the range 1015–1017 cm−3 is presented. This is the first result of mobility calculation in LT GaAs, based on the Monte Carlo method, reported to date. The dependence of mobility on the doping concentration is also presented.

We present a method of simulating the electron transport in low-temperature-grown GaAs by the Monte Carlo method. Low-temperature-grown GaAs contains microscopic inclusions of As and these inhomogeneities render impossible the standard Monte Carlo mobility simulations. Our method overcomes this difficulty and allows the quantitative prediction of electron transport on the basis of principal microscopic material parameters, including the impurity and the precipitate concentrations and the precipitate size. The adopted approach involves simulations of a single electron trajectory in real space, while the influence of As precipitates on the GaAs matrix is treated in the framework of a Schottky-barrier model. The validity of this approach is verified by evaluation of the drift velocity in homogeneous GaAs where excellent agreement with other workers' results is reached. The drift velocity as a function of electric field in low-temperature-grown GaAs is calculated for a range of As precipitate concentrations. Effect of compensation ratio on drift velocity characteristics is also investigated. It is found that the drift velocity is reduced and the electric field at which the onset of the negative differential mobility occurs increases as the precipitate concentration increases. Both these effects are related to the reduced electron mean free path in the presence of precipitates. Additionally, comparatively high low-field electron mobilities in this material are theoretically explained.

In this research, we investigated the growth mechanism of cobalt-doped titanium dioxide (Co:TiO2) films. Thi Co:TiO2 thin films were grown on the n-type silicon substrate. The films were grown by metal organic chemical vapor deposition method. The growth temperature was varied of 325°C – 450°C. The films were characterized by SEM. Using Arheniu's equation, it is known that the activation energy value of film growth is positive in the range of temperature of 325°C – 400°C and negative in the range of temperature of 400°C – 450°C. These results show that the decomposition rate in the range of temperature of 325°C – 400°C is due to diffusion phase of precursor gas. On the other hand, the decomposition rate decreased in the range of temperature of 400°C – 450°C because the precursor gas decreased, and the surface chemical reaction was high.

Metal Organic Chemical Vapor Deposition (MOCVD) is a method for growing a solid material (in the form of thin films, especially for semiconductor materials) using vapor phase metal organic sources. Studies on the growth mechanism of GaAs1-xSbx ternary alloy thin solid film in the range of miscibility-gap using metal organic sources trimethylgallium (TMGa), trisdimethylaminoarsenic (TDMAAs), and trisdimethylaminoantimony (TDMASb) on MOCVD reactor has been done to understand the physical and chemical processes involved. Knowledge of the processes that occur during alloy formation is very important to determine the couple of growth condition and growth parameters are appropriate for yield high quality GaAs1-xSbx alloy. The mechanism has been studied include decomposition of metal organic sources and chemical reactions that may occur, the incorporation of the alloy elements forming and the contaminants element that are formed in the gown thin film. In this paper presented the results of experimental data on the growth of GaAs1-xSbx alloy using Vertical-MOCVD reactor to demonstrate its potential in growing GaAs1-xSbx alloy in the range of its miscibility gap.

SURFACE ROUGHNESS AND GRAIN SIZE CHARACTERIZATION OF ANNEALING TEMPERATURE EFFECT FOR GROWTH GALLIUM AND TANTALUM DOPED Ba0.5 Sr0.5TiO3 THIN FILM. Thin films 10 % gallium oxide doped barium strontium titanate (BGST) and 10 % tantalum oxide doped barium strontium titanate (BTST) were prepared on p-type Si (100) substrates using chemical solution deposition (CSD) method with 1.00 M precursor. The films were deposited by spin coating method with spinning speed at 3000 rpm for 30 seconds. The post deposition annealing of the films were carried out in a furnace at 200 o C, 240 o C, 280 o C (low temperature) for 1 hour in oxygen gas atmosphere. The surface roughness and grain size analysis of the grown thin films are described by atomic force microscope (AFM) method at 5000 nm x 5000 nm area. The rms surface roughness BGST thin films at 5000 nm x 5000 nm area are 0.632 nm, 0.564 nm, 0.487 nm for temperature 200 o C, 240 o C, 280 o C, respectively, whereas the grain size (mean diameter) are 238.4 nm, 219.0 nm, 185.1 nm for temperature 200 o C, 240 o C, 280 o C, respectively. In fact, to increase annealing temperature from 200 o C to 280 o C would result in decreasing the rms roughness and grain size. Therefore, rms roughness and grain size would have the strong correlation annealing temperature.

TiO 2 thin films with its pore coated by copper (Cu) nanoparticles have been developed in order to improve the TiO 2 based solar cells performance. Contact between Cu nanoparticles and TiO 2 play role in minimizing the recombination of electron‐hole pairs and increasing electron transfer in TiO 2 based solar cells. The Cu coating on the space between TiO 2 has been performed by electroplating methods. It is found that the solar cells performance of Cu coated TiO 2 films become higher than of the pure TiO 2 film. The presence of Cu nanoparticles on TiO 2 films were confirmed from Scanning Electron Microscopy (SEM). In this study, a maximum conversion efficiency of 3.73% was achieved.

The GaSb-based material system is attractive for application in photovoltaic (PV) cells since its band gap can be tuned to match the radiation of the emitter. At present, most of the PV cells are fabricated using epitaxial layers and hence are expensive. To reduce the cost, Zn diffusion using elemental vapors in a semiclosed diffusion system is conducted. In this paper, we present studies carried out on Zn diffusion into n-type (Te-doped) GaSb substrates in an open tube diffusion furnace. The diffusion was carried out at a temperature of 600°C, for a diffusion time from 4 to 12 hours. The diffused layers were characterized by current-voltage and capacitance-voltage measurements.

The growth of GaMnN thin films on c-plane sapphire substrate by plasma-assisted metalorganic chemical vapor deposition (PAMOCVD) method is reported. Cyclopentadienyl manganese tricarbonyl (Cp 2 MnT) was used as a source of Mn. The growth was conducted at varied growth temperature in the range of 625 to 700°C and V/III flux ratios between 440 and 1080. The growth rate and Mn incorporation into GaN highly depend on growth parameters. From the analysis of XRD spectra, it was found that the highest Mn incorporation into GaMnN which would produce single phase GaMnN (0002) was 6.4 % at growth temperature of 650°C. While at growth temperature of 700°C, the maximum of Mn incorporation into GaMnN films that would still produce single phase film were 3.2 %. The surface roughness of the films determined from AFM image results showing that high growth temperatures tend to improve the surface morphology of GaMnN. The results of magnetization measurement shows hysteresis behavior at room temperature with various values of coercivity, saturation and remnant magnetization in the range of 350-800 Oe, 20-39 emu/cm3 and 10.2–34.4 emu/cm3, respectively depend on the Mn concentration. For the films grown at 650 °C, the highest magnetic moment per Mn-atom was obtained by a sample with Mn concentration of 2.0 %, i.e. 3.1 µ Β /Mn-atom. While for the films grown at 700°C, the highest magnetic moment per Mn-atom was obtained by a sample with Mn concentration of 2.5 %, i.e. 3.7 µ Β /Mn-atom.

This paper reported the study of growth of Al x Ga 1−x N thin film on a-plane sapphire substrate using plasma assisted metal organic chemical vapor deposition (PA-MOCVD). We have successfully growth the Al content AlGaN alloys and investigated the influence of TMA/TMAl+TMGa flow rate ratio to their crystal structure and surface morphology. From S EM image and XRD measurement, the AlGaN films grown with TMA/TMAl+TMGa flow rate ratio of 20% have single crystal orientation, homogeneous and smoother surface morphology. From ED X microanalysis results, all of the AlGaN alloys have high Al content. The Al content of the AlGaN alloys with TMA/TMAl+TMGa flow rate ratio of 20%, 30%, and 40% is about x = 0.5, 0.6, and 0.65, respectively and grown at the growth temperature about of 700°C.

Nanostructures have become a topic of increasing interest due to their fundamental properties and possible device applications. One method of fabrication that is receiving much attention lately is the utilization of the coherent Stranski-Krastanov mode which leads to self-assembly of small-scale islands, driven by the lattice mismatch between the quantum dot material and the underlying substrate material [1–5]. W e quantitatively investigate initial stages of growth and evolution of GaSb islands on GaAs substrates grown by metalorganic chemical vapor deposition (MOCVD). We pay particular attention to the transition from 2D to 3D growth and to the transition between isolated island growth and the coalescence of islands in an effort to improve our understanding of this regime. The extent of oxidation and growth derived oxygen contamination for GaSb quantum dots grown by metalorganic chemical vapour deposition (MOCVD) were also investigated by X-ray photoelectron spectroscopy (XPS) using a system with high energy resolution.

EpitaxialAlxGa1-xSb layers on GaAs substrate have been grown by atmospheric pressure metalorganic chemical vapour deposition using TMAl, TMGa, and TMSb. We report the effect of V/III flux ratio and growth temperature on growth rate, surface morphology, electrical properties, and composition analysis. A growth rate activation energy of 0.73 eV was found. For layers grown on GaAs at 580∘C and 600∘C with a V/III ratio of 3 a high quality surface morphology is typical, with a mirror-like surface and good composition control. It was found that a suitable growth temperature and V/III flux ratio was beneficial for producing good AlGaSb layers. Undoped AlGaSb grown at 580∘C with a V/III flux ratio of 3 at the rate of 3.5 μm/hour shows p-type conductivity with smooth surface morphology and its hole mobility and carrier concentration are equal to 237 cm2/V.s and 4.6 × 1017 cm-3, respectively, at 77 K. The net hole concentration of unintentionally doped AlGaSb was found to be significantly decreased with the increased of aluminium concentration. All samples investigated show oxide layers (Al2O3,Sb2O3, andGa2O5) on their surfaces. In particular the percentage of aluminium-oxide was very high compared with a small percentage of AlSb. Carbon content on the surface was also very high.

GaNxAs1-x thin films had been successfully grown on semi-insulating GaAs (001) substrates by metal organic chemical vapour deposition (MOCVD) method. The precursors used were trimethylgallium (TMGa), dimethylhydrazine (DMHy), and tris-dimethylaminoarsenic (TDMAAs). GaNxAs1-x thin films of 1.2-2.4 mum thick were grown at the total reactor pressure of 50 torr, H2 and N2 flow rate of 300 sccm, temperatures range of 560 - 590degC, and the ratio of TDMAAs/TMGa and DMHy/TDMAAs flow rate of 4.5 and 0.8, respectively. The growth rate of GaNxAs1-x thin films are in the range of 0.8 - 1.6 mum/h. The N concentration of GaNxAs1-x thin films was studied by HR-XRD measurements and was calculated using Vegard's law from symmetric and asymmetric reflection. From this study, it found that the N concentration of GaNxAs1-x thin films were in the range of 4.9 and 5.5%. The measured electron mobility using Hall-van der Pauw method is in order of 3270 and 3380 cm2 V-1 s-1 at x = 4.9% and 5.5%, respectively.

Co-doped TiO2 thin films were grown on Si(100) substrates by MOCVD method using titanium (IV) isopropoxide [Ti(OCH(CH3)2)4] and tris (2,2,6,6-tetramethyl-3, 5-heptanedionato) cobalt (III), Co(TMHD)3 precursors. The growth parameters, crystal structure, ferromagnetic and electrical transport properties of thin films were investigated. Ferromagnetic behaviors of films were observed at room temperature. Magnetic and structural properties strongly depend on the Co concentration and the growth temperature. Epitaxial thin films with highest magnetic saturation were found on the films grown at temperature of 450 C. Resistivity as a function of temperature measurement shows that the films have semiconducting properties.

Growth of GaN quantum dots on AlGaN layer using [(C2H5)4]Si [TESi] by plasma assisted metal organic chemical vapor deposition (PA-MOCVD) is reported. The surface profile of the grown GaN quantum dot was determined by atomic force microscope (AFM). The typical average density of the dots is around 4 109 cm-2, while the diameter and the height of the dots are approximately 100 and 50 nm, respectively. The density and the size of the dots significantly depend on the dose of TESi. It is found that the growth mode was changed from the two-dimensional step-flow to the three-dimensional island formation by modifying the AlGaN surface energy induced by the deposited Si.

The effect of Mn incorporation into GaN:Mn thin films on their structural property, surface morphology and magnetic property are presented. The GaN:Mn thin films were grown by plasma-assisted metalorganic chemical vapor deposition (PA-MOCVD) using Trimethylgallium (TMGa), nitrogen (N2) and cyclopentadienyl manganese tricarbonyl (CpMnTc) as a source of Ga, N and Mn, respectively. The grown films have Mn concentration as high as 6.6%. The maximum Mn concentration that still produces single phase GaN:Mn (0002) depends on growth temperature. The highest concentration of Mn atoms which are incorporated in the wurtzite structure substitutionally is 2.5%. Above this concentration, parts of Mn atoms are incorporated into GaN matrix intertitially. The surface roughness of the films determined from the AFM images show that the film with 6.4% of Mn has a better surface morphology than that of the film with 6.6 % of Mn. The results of magnetization measurements show hysteresis behavior at room temperature. The maximum of magnetic moment is achieved by the film with Mn concentration of 2.5 %

Most of the growth of GaN epilayers by MOCVD method reported to date was carried out at growth temperature above 1000/spl deg/C on sapphire substrates. We have successfully grown GaN by plasma assisted MOCVD (PA-MOCVD) method at temperature between 560/spl deg/C to 650/spl deg/C. In this paper we report an attempt to fabricate Au/n-GaN Schottky diode grown on Si(111) by PA-MOCVD method. The GaN films were grown at temperatures of 625/spl deg/C and 650/spl deg/C using trimethylgallium (TMGa) and nitrogen plasma. The diode is a concentric type using aluminum as ohmic contact and gold as Schottky contact. Electrical characterizations were performed by I-V and C-V measurements. The barrier heights determined from I-V measurements are 0.44 eV and 0.49 eV, for Schottky diodes grown at 625/spl deg/C and 650/spl deg/C, respectively. The ideality factors are 4.5 and 5.6 indicate that tunneling as the main mechanism of electron transport through the barrier. This mechanism is typical for moderately to highly doped semiconductor, as confirmed from C-V measurement.

Thin films Al/sub x/Ga/sub 1-x/N were grown on (0001) sapphire substrates by plasma assisted metal-organic chemical vapor deposition (PA-MOCVD). Plasma-cracked N/sub 2/, trimethylaluminum (TMAl) and trimethylgallium (TMGa) were used as nitrogen, aluminum and gallium sources, respectively. The results of energy dispersive X-ray (EDX) measurements performed at room temperature yielded the linear dependence of molar fraction of Al (x) on molar fraction of vapor phase of TMAl/(TMAl + TMGa). The dependence of the band gap energy on the molar fraction of Al (x) showed quadratic expression, E/sub g/ (x) = 3.35 + 1.55x + 1.3x/sup 2/ eV. Al/sub x/Ga/sub 1-x/N layers with x < 0.34 show n-type conduction with room temperature mobilities in the range of 5 to 10 cm/sup 2//V/spl middot/s, and electron concentrations of 9.0 /spl times/ 10/sup 16/ to 1.4 /spl times/ 10/sup 19/cm/sup -3/.

We have probed transport mechanisms in Al/low temperature (LT) grown GaAs/n/sup +/GaAs Schottky diodes through their I-V characteristics as a function of temperature and through their AC conductivity at room temperature. The structures show features of rectification and series resistance. The former is analysed in terms of thermionic emission-tunneling theory and shows the temperature dependent ideality factor close to three, characteristic of tunneling through the depletion barrier of the n/sup +/ substrate. Electrons are injected through this barrier into gap states in the LT GaAs layer. The series resistance versus temperature shows an Arrhenius type behaviour with an activation energy of 32 meV, while the frequency-dependent AC conductivity behaves as /spl omega//sup s/ with s=0.65. These observations are consistent with hopping through gap states.

MBE grown low temperature GaAs layers have been annealed at various temperatures up to 600/spl deg/C and their structural and transport properties examined. Excess As precipitation is confirmed by TEM measurements. Both hopping and band transport are present in the material annealed at temperatures up to 500/spl deg/C. The measured mobility for 600/spl deg/C annealed material agrees well with predictions of Monte Carlo calculations taking full account of precipitate scattering.

We have grown a heterostructure of YBCO/STO/YBCO on (100) MgO substrate for fabrication of SXS junction. The epitaxial YBCO films were grown by MOCVD method, and the STO layer was deposited by unbalanced magnetron sputtering method. All of films are dominated by a-axis oriented phases. The individual YBCO films revealed critical-current densities around 2.5 X 105 A/cm2 at 77 K. The resistive transition observed in the vertical transport devices is dominated by the X layer properties. These devices display RSJ-type I-V characteristics and the values of IcRn significantly depend on the X layer thickness. The SXS junction with STO layer of 0.1, 0.2 and 0.3 micrometers have IcRn of 115, 90 and 42 (mu) V, respectively.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have studied the influence of hydrogen plasma treatment and annealing on GaN mms grown by plasma-assisted metal organic chemical vapor deposition (MOCVD). The X-ray diffraction (XRD) pattern of GaN films grown without assistance of hydrogen plasma show misoriented polycrystalline structure, while those grown with the assistance of hydrogen plasma show a crystalline structure with (0001) orientation. Post-growth hydrogenation and annealing reduces the carrier concentration of fUms grown without hydrogen plasma, but does not give a significant effect for mms grown with the assistance of a hydrogen plasma.

The efficiency of titanium dioxide (TiO2)-based film solar cells fabricated by combined spray and electroplating methods was improved by forming metal bridges in the pores between TiO2 nanoparticles. The interfaces between TiO2 nanoparticles and metal bridges formed Schottky contacts, which minimized recombination of electron-hole pairs and increased electron transfer. A maximum efficiency of 4.38% was achieved for cells plated at 50 mA and 55 °C. This efficiency is higher than that reported for solar cells with a similar structure [Saehana et al., AIP Conf. Proc. 1284, 154 (2010); 1415, 163 (2011); IJBAS/IJENS 11, 15 (2011)]. We also identified that both current and temperature influence the morphology of the metal bridges and efficiency of the solar cell.

In this paper we have grown pure Ba 0.25 Sr 0.75 TiO 3 (BST) and BST doped by Ferric Oxide Fe 2 O 3 (BFST) with doping variations of 5%, 10%, and 15% above type-p Silicon (100) substrate using the chemical solution deposition (CSD) method with spin coating technique at rotation speed of 3000 rpm, for 30 seconds. BST thin film are made with a concentration of 1 M 2-methoxyethanol and annealing temperature of 850 o C for the Si (100) substrate. Characterization of the thin film is performed for the electrical properties such as the current-voltage (I-V) curve using Keithley model 2400 as well as dielectric constant, time constant, pyroelectric characteristics, and depth measurement. The results show that the thin film depth increases if the concentration of the Ferric Oxide doping increases. The I-V characterization shows that the BST and BFST thin film has photodiode properties. The dielectric constant increases with the addition of doping. The maximum dielectric constant value is obtained for 15 % doping concentration namely 83.1 for pure BST and 6.89, 11.1, 41.63 and 83.1, respectively for the Ferric Oxide doping based BST with concentration of 5%, 10%, and 15%. XRD spectra of 15% of ferric oxide doped BST thin film tetragonal phase, we carried out the lattice constant were a = b = 4.203 A; c = 4.214 A; c/a ratio = 1.003. Received: 01 February 2010; Revised: 04 October 2011; Accepted: 02 November 2011

In this paper, we report the characteristics of GaN heteroepitaxial films grown on Si(111)at 700oC using plasma-assisted metalorganic chemical vapour deposition (PA-MOCVD). In this growth technique, H2 plasma was used in addition to N2 plasma. Two sets of samples with different buffer layers were used, i.e. GaN and AlN buffer layers. In the infrared region both samples exhibit similar reststrahlen band shape. However the sample with GaN buffer layer exhibits better optical properties in the visible region compared with its counterpart. This is attributed to its better structural bulk and surface properties.

In this paper, we investigated the effect of reactive hydrogen plasma, used in the thermal cleaning process of the substrate, on the optical properties of gallium nitride (GaN) films deposited on c-plane sapphire substrates in the reststrahlen and near bandgap regions. The GaN films were grown at 700 C by plasma-assisted metal organic chemical vapour deposition. IR reflectance and absorption measurements were conducted to study the optical properties in the reststrahlen and near bandgap region respectively. Since the optical properties of a material greatly depend on its structural properties, X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements were also performed as a comparison to the optical results. In addition, Hall effect measurements using the van der Pauw configuration were conducted to obtain the carrier density and mobility of the GaN films.