Electrochemical C——V Characteristics and Photoluminescence of a—C ： N Films

Amorphous carbon (a—C) films and amorphous carbon films incorporating with the nitrogen (a-C : N) were deposited on silicon substrates in a radio-frequency driven plasma enhanced chemical vapour deposition system, while the surface electrical properties of films were investigated by electrochemical capacitance-voltage measurements. It was examined the effect of the interface defects on the properties and deduced that the conducting type of a--C : N films was n--type. Subsequently, a comparative studies of a--C and a- C : N films were performed by photoluminescence spectra depending on the temperature. With the decrease of the temperature, the main band with peak energy of 2.48 eV in the a-C：N films was more intense compared with the other three bands caused by amorphous C in the a-C films.     

Size Control of Nanoscale Silicon Particles Formed in Thermally Annealed A-Si∶H Films and Its Photoluminescence

A method to control the si ze of nanoscale silicon grown in thermally annealed hydrogenated amorphous silico n (a-Si∶H) films is reported. Using the characterizing techniques of micro-Ra man scattering, X-ray diffraction and computer simulation, it is found that the sizes of the formed silicon particles change with the temperature rising rate i n thermally annealing the a-Si∶H films. When the a-Si∶H films have been anne aled with high rising rate( ~100 ℃/s), the sizes of nanoscale silicon particle s are in the range of 1.6~15 nm. On the other hand, if the a-Si∶H films have been annealed with low temperature rising rate(~1 ℃/s), the sizes of nanoscale silicon particles are in the range of 23~46 nm. Based on the theory of crystal nucleation and growth, the effect of temperature rising rate on the sizes of th e formed silicon particles is discussed. Under high power laser irradiation, in situ nanocrystallization and subsequent nc-Si clusters are small enough for vis ible light emission, authors have not detected any visible photoluminescence(PL) from these nc-Si clusters before surface passivation. After electrochemical ox idization in hydrofluoric acid, however, intense red PL has been detected. Cycli c hydrofluoric oxidization and air exposure can cause subsequent blue shift in t he red emission. The importance of surface passivation and quantum confinement i n the visible emissions has been discussed.     

Synthesis and Characterization of SiCOF/a-C∶F Double-Layer Films with Low Dielectric Constant for Copper Interconnects

用等离子体化学气相淀积系统制备了一种新颖的SiCOF/a-C:F双层低介电常数介质薄膜,并用红外光谱表征了该薄膜的化学结构.通过测量介质的折射率发现该薄膜长时间暴露在空气中,其光频介电常数几乎不变.然而,随退火温度的增加,其光频介电常数则会减小.基于实验结果讨论了几种可能的机理.二次离子质谱分析表明在Al/a-C:F/Si结构中F和C很容易扩散到Al中,但在Al/SiCOF/a-C:F/Si结构中,则没有发现C的扩散,说明SiCOF充当了C扩散的阻挡层.分析还发现在SiCOF和a-C:F之间没有明显的界面层.     

Raman Scattering and Photoluminescence in Ge-implanted GaN Films

The investigations on Ge-implanted GaN films grown by MOCVD and then annealed at 1100℃ under ammonia ambient have been carried out. With increasing Ge implantation dose, four additional peaks arise at wave numbers of 260, 314, 428 and 670cm-1 in Ramam spectra. In PL spectra, the relative intensity of the band-edge emission compared to the PL-band centered at 2.66eV and the yellow band decreases with increase of Ge-implanted dose. The modes of 260 and 314cm-1 are attributed to disorder-activated Raman scattering, whereas the modes of 428 and 670cm-1 are assigned to local vibrations of vacancies and vacancy-related complexes. The PL-band centered at 2.66eV and the yellow band is also related to these vacancy defects. The new Raman peak at 301cm-1 for the sample annealed only 5min originates from Ge clusters due to deficient annealing.     

Fabrication of Alq3／PBD OMQW Structures and Its Photoluminescence Characteristics

Organic multiple quantum well(OMQW)structures consisting of alternating layers of tris(8-quinolinolato)aluminum(Ⅲ）（Alq3)an 2-(4-biphenylyl)-5-(4-ter-butylphenyl)-(1,3,3-oxadiazole)(PBD)have been fabricated by organic molecular beam deposition(OMBD).The individual layer thickness in the multilayer samples was varied from 6 nm tp 20nm.The multiple quantum well structures were determined by low angle X-ray diffraction,optical absorption and photoluminescence(PL).The PL spectra narrow and the emission energy has been observed to shift to higher energy compared with that in the monolayer structure,suggesting a quantum size effect.     

The Quantum Dots Characteristics of Hydrogenated Nanocrystaline Silicon Films

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Q-switched and Mode-locked Characteristics of Cr~(4+)∶YAG Crystal

The passively Q-switched and mode-locked(QML) characteristics in a diode-pumped Nd∶GdVO_4 laser with Cr~(4+)∶YAG saturable absorbers have been demonstrated. A maximum average output power of 710mW has been obtained in the QML laser. The maximum energy of a single Q-switched pulse is 52.5μJ, with the corresponding pulse width of 30ns and the peak power of 1.75kW, at the incident pump power of 7.75W. The repetition rates of the Q-switched envelope and the mode-locked laser pulse are 16.7kHz and 680MHz, respectively.     

Effect of Film Thickness on Properties of a-Si∶H Films

The a-Si∶H films with different thickness smaller than 1 μm were deposited by plasma enhanced chemical vapor deposition (PECVD) under the optimum deposition conditions. The effect of different thickness on film properties is analyzed.The results show that,with the increase of the film thickness,the dark conductivity, photoconductivity and threshold voltage increase, the optical gap and peak ratio of TA to TO in the Raman spectra decrease, the refractive index keeps almost constant, and the optical absorption coefficient and current ratio of on/off state first maximize and then reduce.     

Size Control of Nanoscale Silicon Particles Formed in Thermally Annealed A-Si ： H Films and Its Photoluminescence

A method to control the size of nanoscale silicon grown in thermally annealed hydrogenated amorphous silicon （a-Si：H） films is reported. Using the characterizing techniques of micro-Raman scattering, X-ray diffraction and computer simulation, it is found that the sizes of the formed silicon particles change with the temperature rising rate in thermally annealing the a-Si ： H films. When the a-Si：H films have been annealed with high rising rate（～100℃/s）, the sizes of nanoscale silicon particles are in the range of 1.6～15nm. On the other hand, if the a-Si：H films have been annealed with low temperature rising rate（～1℃/s）, the sizes of nanoscale silicon particles are in the range of 23～46nm. Based on the theory of crystal nucleation and growth, the effect of temperature rising rate on the sizes of the formed silicon particles is discussed. Under high power laser irradiation, in situ nanocrystallization and subsequent nc-Si clusters are small enough for visible light emission, authors have not detected any visible photoluminescence（PL） from these nc-Si clusters before surface passivation. After electrochemical oxidization in hydrofluoric acid, however, intense red PL has been detected. Cyclic hydrofluoric oxidization and air exposure can cause subsequent blue shift in the red emission. The importance of surface passivation and quantum confinement in the visible emissions has been discussed.     

Characteristics and Electrical Properties of SiNx：H Films Fabricated by Plasma-Enhanced Chemical Vapor Deposition

SiNx：H films with different N/Si ratios are synthesized by plasma-enhanced chemical vapor deposition （PECVD）. Composition and structure characteristics are detected by Fourier transform infrared spectroscopy （FTIR） and X-ray photoelectron spectroscopy （XPS）. It indicates that Si-N bonds increase with increased NH3/SiH4 ratio. Electrical property investigations by I-V measurements show that the prepared films offer higher resistivity and less leakage current with increased N/Si ratio and exhibit entirely insulating properties when N/Si ratio reaches 0.9, which is ascribed to increased Si-N bonds achieved.     

High Purity and Large-scale Preparation of β-Ga2O3 Nanowires and Nanosheets by CVD and Their Raman and Photoluminescence Characteristics

Ga2O3 nano-structures, nanowires and nanosheets are produced on Au pre coated（111） silicon substrates with chemical vapor deposition（CVD） technique. By evaporating pure Ga powder in the H2O atmosphere under ambient pressure the large-scale preparation of β-Ga2O3 with monoclinic crystalline structure is achieved. The crystalline structures and morphologies of produced Ga2O3 nano-structures are characterized by means of scanning electron microscope（SEM）, X-ray diffraction（XRD）, selected area electron diffraction （SAED） and transmission electron microscope（TEM）. Raman spectrum reveals the typical vibration modes of Ga2O3 The vibration mode shifts corresponding to Ga2O3 nano-structures are not found. Two distinguish photoluminescence（PL） emissions are found at about 399 nm and 469 nm owing to the VO-VGa excitation and VO-VGaO excitation, respectively. The growth mechanisms of Ga2O3 nanowires and nanosheets are discussed with vapor liquid-solid（VLS） and vapor-solid（VS） mechanisms.     

Photoluminescence and X-ray Diffraction of Distributed Bragg Reflector

Spectral and structural characteristics of distributed Bragg reflector (DBR) in vertical-cavity surface-emitting lasers were studied with photoluminescence and double- crystal X- ray diffraction measurement. The expected high quality epitaxial DBR structure was verified. In the X- ray double- crystal rocking curves of DBR the zeroth- order peak, the first and second order satellite peaks were measured. Splitting of diffraction peak appeared in the rocking curves was analyzed. The effects of introduced deep energy levels on the structural perfection and optical properties were discussed.     

Electrodeposition and Characterization of ZnO Thin Films

Thin films of ZnO were electrodeposited from an aqueous solution of Zn（NO3 ）2 on indium tin oxide（ITO）-covered glass substrate. The analysis of X-ray diffraction（XRD） and scanning electron micrograph （SEM） indicated that the obtained ZnO films had a compact hexagonal wurtzite type structure with preferable （002） growth direction. A sharp near-UV emission peak located at 380 nm and a strong orange-red emission peak located at 593 nm were observed in the photoluminescence, when excited with 325 nm wavelength at room temperature. Then the prepared ZnO films were introduced as anode phosphors into the field emission test. It was found that orange-red cathode-luminescence was observed and the luminescent brightness was enhanced by annealing. When annealing temperature increased about 600 ℃, the photoluminescence with peak of 531 nm and the green cathode-luminescence were observed. The tests showed that the brightness of about 2 × 102 cd/m^2 was obtained at electric field of 2 V/μm for annealed sample. The results revealed that the film could be a good kind of low-voltage drived cathode-luminescence phosphor.     

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4–P(VDF-TrFE) Nanocomposite Films

Polymer–ceramic nanocomposites play an important role in embedded capacitors. However, polymer–ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]–CoFe₂O₄ (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer–ceramic nanocomposite films of controllable thickness.     

Characteristics of Polyaniline/Si Heterojunction Solar Cell By Electrochemical Dye Sensitization

Using the electrochemical polymerization dye sensitization （ECDS） method, polyaniline （PAn）, which is used as top region material in solar cells, is sensitized with direct blue dye（DS）, and sensitized Al grid/DS-PAn/n-Si/Al heterojunction solar cells is prepared by ECDS. Influences of the ECDS on the absorption spectrum and the junction characteristics of the solar cell were discussed, and the output characteristics were measured. The results show that the absorption spectrum of the sensitized PAn films is much wider and stronger in Vis-range; the diode quality factor is about 6.3 and the height of latent barrier potential of p-n junction is 0.89 eV; the short-circuit current and the conversion efficiency of sensitized DS- PAn/Si heterojunction solar cells are greatly improved, which the short-circuit current can increase 6 times, the fill factor is 57% and the efficiency can reach 1.42 % under the illumination of 37.2 W/m^2 , respectively.     

Studies and Application of Characteristics of Absorbing Materials

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Evolution of Structural,Optical and Electrical Characteristics of Spin-Coated CdO Thin Films with the Gelation State of the Sol–Gel

The present work is intended to investigate the influence of the gelation state of the sol–gel on the properties of spin-coated cadmium oxide (CdO) thin films. The viscosity of the sol–gel increases at a slow uniform rate up to 5 days (break-off point) after which the rise becomes progressively more rapid and it attains saturation after 10 days of gelation. Films have been grown with gelation times of 2 days, 4 days, 6 days, 8 days, 9 days and 10 days. The visual characteristics of the films have been discussed in terms of the centrifugal force acting on the sol–gel. The sol–gel viscosity seems to be better suited to represent the gelation state of the sol–gel rather than the gelation time. The x-ray diffraction studies show that lower gelation times and lower sol–gel viscosities give rise to single crystalline CdO thin films while gelation times of 6 days and above (i.e. sol–gel viscosities of 2.92 × 10^?3 N s m^?2 and more) yield polycrystalline CdO thin films. The gelation state of the sol–gel has been found to have a strong bearing on the properties of CdO thin films, and highly conducting and transparent CdO thin films can be achieved by controlling the gelation state of the sol–gel and the results obtained have been reported.     

Degradation of the Photoluminescence of ZnTPP and ZnTPP–C<Subscript>60</Subscript> Thin Films under Gamma Irradiation

Porphyrins and their fullerene complexes are promising materials for organic photovoltaic structures. However, the stability of the properties of organic components under hard radiation is poorly studied. Here, the influence of γ irradiation with medium (about 10⁴ Gy) and large (10⁷ Gy) doses on the photoluminescence of thin structurally perfect films of both pure porphyrin ZnTPP and ZnTPP/C₆₀ composite films in the molar ratio of 1.3: 1 is investigated. It is shown that the intensity of the electronic radiative transition (626 nm) decreases under the effect of γ irradiation, and the dose dependence is threshold. The threshold dose is ~20 kGy for the ZnTPP films. The intensity of the electron-vibrational part of the spectral dependence of the PL (670–690 nm) for both types of samples decreased at initial irradiation doses and decreases less with a further increase in the irradiation dose than for the purely electron transition. The addition of a fullerene in nanocomposite films increases the threshold dose, after which the PL of the films started to degrade, by a factor of ~2.5. Herewith, the spectral components of the PL associated with the manifestation of the radiation transition of the fullerene C₆₀ are more stable under γ irradiation.     

Effect of Substrate Temperature on Optical Characteristics of Silver Island Films for Harvesting Solar Energy

Due to their particular optical characteristics,metallic island films have the potential to significantly increase the energy conversion efficiency of solar cell.We experimentally and theoretically investigated the effect of substrate temperature on the morphologies and optical properties of the silver island films.At low temperature,below 300 ℃,as the substrate temperature increases.Compared to the films prepared at room temperature,the sizes of nanoparticles decrease and the Absorption peaks shift to shor...     

Growth and Optical Properties of ZnO Films and Quantum Wells

研究了用MOCVD法在蓝宝石(Al2O3)(0001)和(1120)衬底上制备ZnO薄膜时的生长特性.详细研究了采用Al2O3(0001)衬底时生长温度与压力的影响.由于存在比较大的晶格失配,一般容易得到ZnO纳米结晶,不容易获得既平坦且质量又好的ZnO薄膜.生长温度对薄膜-衬底界面的生长模式有很大的影响;而生长压力对ZnO纳米结晶的形状有决定性作用.通过适当控制生长温度及压力,可以得到ZnO薄膜或不同形状的纳米结构.当采用Al2O3(1120)衬底时,由于晶格失配较小,能保持平坦层状生长,临界膜厚远远大于采用Al2O3(0001)衬底的结果.在Al2O3(1120)衬底上制作了ZnO/MgZnO量子阱并研究了其光学特性.观察到了量子化能级间以及在载流子间的跃迁引起的发光.由压电效应引起的内建电场约为3×105V/cm.同时发现采用低温低压生长可以增大ZnO中受主杂质浓度,有利于获得p型ZnO.