Thin film solar cells, if film thickness is thinner than the optical absorption length, typically give lower cell performance. For the thinner structure, electric current loss due to light penetration can offset the electric current gain obtained from higher built-in electric field. Light trapping schemes can increase the effective optical absorption length and thus enhance the electric current for thinner solar cells. Here a new light trapping scheme based on light trapping transparent conducting oxide layer (LT-TCO) is proposed to enhance the performance of thin film solar cells. Three different configurations of integrating the LT-TCO layer in solar cells are proposed and evaluated. This research aims to develop the LT-TCO layer with surface texture and good conductivity by pulsed laser deposition (PLD) technique at low temperature. The LT-TCO layer is fabricated by PLD deposition of Al-doped ZnO to achieve multilayer films by tuning of oxygen pressure. The light trapping effect is examined by optical transmittance measurement and the surface texture is characterized by transmission electron microscopy (TEM) technique. The conductivity of LT-TCO layer is measured by resistivity measurement. Thin film CdTe/CdS solar cells are fabricated by PLD technique to develop baseline solar cells for integration of LT-TCO layer. The as-deposited thin film solar cells show relatively low performance and are further processed with various post-deposition treatments to seek efficiency enhancement. The effects of different processes on cell performance are examined by electrical, optical, and microstructure studies. Air annealing of CdS layer and CdCl2 treatment of CdTe layer combined are found to yield the best cell performance. The fabrication issues that limit the cell performance are discussed and future optimizations in fabrication processes are suggested.

In the last years, intensive research on new tunable solid state laser materials has been carried out. For the spectral range from 1300 to 1600 nm the Cr4+ ion seems to be the most promising laser-ion. In order to meet the the demand of broad-band devices, we employed the Cr4+ doped YAG crystal fibers with high optical quality thin films design and coating (high index material TiO2, low index material SiO2) to achieve the development of high efficiency crystal fiber lasers. In this thesis, crystal fiber was used as the laser gain medium, and coated with optical thin films at both end faces (input face 900-1100 nm AR and 1300-1600 nm HR; output face 1300-1600 nm HR) as the laser cavity to reduce the loss and promote laser efficiency. During the experiment, we tried to optimize the coating conditions to acquire high density, stable index and low absorption coefficient thin films. With different thin film thickness and stacking designs, the electric field distribution was designed to be away from the laser interface and high index region to increase the laser-induced damage threshold and lifetime for high power pumping. In addition, CaO and Cr2O3 were deposited on Cr4+:YAG source rods before the laser-heated-pedestal growth to increase CaO and Cr2O3 doping concentration for higher fluorescence efficiency and signal saturation power.

Aluminum nitride (AlN) thin film is a promising material as buffer layer in GaN-based optoelectronic and electronic devices or as a substrate to fabricate Surface Acoustic Wave (SAW) and Film Bulk Acoustic wave Resonant (FBAR) devices in high frequency in wireless (>1GHz) communication technology. Aluminum nitride, thin film with the c-axis normal to the film is favored in a low energy deposition condition because it places the packed hexagonal basal plane parallel to the substrate surface. Grains of this orientation have a low surface energy which favors rapid growth in a columnar structure. In this experiment r.f. dual ion beam sputtering (DIBS) system is used to prepare the AlN films on Si (100) substrate. Various processing variable were tested to deposit AlN films with desirable properties. After systematic testing, a high quality film with preferred c-axis orientation was grown successfully on Si (100) substrate with Al target under the process parameters of 700 ev energy flux; 55% N2 / (N2+Ar) ratio; 4X10 - 4 torr working pressure with no heating of substrate. The AlN target is also used. The results show the great sensitivity of the films to oxygen-containing environments. Only under low residual oxygen pressure, could aluminum nitride be grown well. The deposited AlN thin film characteristic were studied by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Electron Spectroscopy for Chemical Analysis (ESCA).

In This study a thin film of nanometric TiO2 was sol-gel prepared and used for heterogeneous photocatalytic reaction to treat chlorobenzene in testing solution and to evaluate its removal efficiency. Conventionally, the material of photocatalyst was mainly fabricated in form of powder used in the suspension system. Although TiO2 powder has a high specific surface area for heterogeneous photocatalysis, it still leaves a great number of suspended solids in solution awaiting proper handling after the treatment is completed. Also, such suspended solids would pose ¡§shielding¡¨ effect from UV light, and thus affected the efficiency of photocatalytic degradation. To overcome this drawback, a proper mesh size of stainless steel webnet was first selected as a treatment substrate and TiO2 dip-coated, followed by calcination at 500¢J. The end product was used as the TiO2 photocatalytic film for this study. The film of TiO2, verified as anatase type of crystal lattice by XRD and SEM, contained particle sizes ranging from 10 to 20 nm. A solution containing chlorobenzene was used in the study to assess the extent of photocatalytic degradation by UV/TiO2 film. The test was to evaluate the effects of the number of dip-coating and calcining (thickness), initial pH, UV light intensity (@365 nm), and applied electric voltage on photocatalytic removal of chlorobenzene in the solution. The test results indicated that TiO2 film was capable of degrading chlorobenzene; however, enhancement of the degradation efficiency was found to be needed. It was also found that the degradation rate of chlorobezene increased with an increasing thickness of the film and UV light intensity. The pH of test solution was found to be insensitive to degradation of chlorobenzene, probably due to its non-dissociation nature. It was found that electric voltage exerted was unable to prevent electrons and holes from re-combining, and a negative effect of external voltage was even observed. Therefore, it was believed that voltage exertion was not beneficial to phtocatalysis in this study. Kinetics of the tests in this study assumed a pseudo-first-order reaction, which resulted in a rate constant k' = 1.3¡Ñ10-5¡]min-1¡^. The reaction rate was found to be proportional to the 0.7507 order of UV light intensity.

The primary target of this paper is to fabricate bidirectional transceiver modules based on single mode fiber (SMF) and ultra-thin thin-film filter (TFF). Two major components, namely, SMF and ultra-thin TFF are hybrid integrated on the silicon bench using V-groove and U-groove techniques. A 1310 nm wavelength light was launched into the input SMF of the module. After passing through the filter, the light was received by the output SMF of the module. On the other hand, a 1550 nm wavelength light input to the SMF is reflected by the filter and collected by the output multimode fiber (MMF). Transceiver modules using two different fiber structures were fabricated. The first kind of the module uses standard SMF for 1310 nm light transmission. The insertion loss of the module for the 1310 nm wavelength light was 5.66 dB. In the second kind of the module lens fibers were used to replace the standard SMF. The insertion loss for the 1310 nm wavelength light was reduced to 0.98 dB. A reduction of 4.6 dB was achieved. For both modules, the insertion loss for the 1550 nm wavelength light reflected from the filter was around 0.5 dB.

Recently, there are great demands for RF band pass filters with smaller size/volume, lighter weight, and higher performance for advanced mobile/wireless communication system. However, fabricated RF filters using traditional lumped element, dielectric resonators, or surface acoustic wave¡]SAW¡^filters have difficulties in on-chip integration, power handling capability, and temperature compensation. Alternatively, thin-film bulk acoustic wave resonator¡]FBAR¡^filters are very suitable devices for MMIC¡¦s since they can be fabricated on Si or GaAs substrates at a lower magnitude than lumped elements or dielectric resonators, plus they have a much lower insertion loss and higher power handling capabilities than surface acoustic wave devices and full integration with other CMOS RF IC circuitry for realizing a goal of system on chip¡]SOC¡^. In their simplest form, practical FBARs consist of a sputtered piezoelectric thin film sandwiched between top and bottom electrodes onto which an electric field is then applied. An FBAR must have two acoustically reflecting surfaces in order to trap energy and produce resonating characteristics. For this purpose, the thin film bulk acoustic resonator has to be isolated acoustically from the substrate. In view of this, in order to obtain a high Q factor and reduce spurious responses, this paper proposed the air gap type resonator using the sacrificial layer etching. The thickness of the AlN thin film used for piezoelectric thin film of Air-gap FBAR is 1um. Pt/Ti with 3000Å/300Å thickness is used as the top and bottom electrode. The device has a resonance frequency of 1.2GHz, and S11-paparameter of -25dB is also obtained.

The primary target of this paper is to fabricate triplexer modules based on Si-bench technology. The triplexer modules were formed by hybrid integration of single mode lensed fibers and ultra-thin thin-film filters (TFF) on silicon bench as using V-groove and U-groove techniques. The output light at 1.31 µm was launched into the input lensed fiber of the module. After passing through two filters, the light was received by the output lensed fiber of the module. The insertion loss of the module at the 1.31 µm light was 1.25 dB. On the other hand, incoming lights at 1.49µm and 1.55µm were received from the output lensed fiber. Lights at 1.49µm will pass through the first filter, and be reflected by the second filter, and eventually be collected into the second multimode fiber. The insertion loss of the module at the 1.49 µm light was 1.14 dB. The 1.55µm wavelength lights received at the lensed fiber are reflected by the first filter and collected by the first multimode fiber. The insertion loss of the module at the 1.55 µm light was 0.68 dB.

In this study , we investigate the relationship between growth condition and thin film quality of cadmium sulfide (CdS) thin films grown by chemical bath deposition (CBD) method. Thin film structures are analyzed by X-ray diffraction , morphology and grain size are obtained by scanning electronic microscopy , and film thickness measured by reflectance spectroscopy . In medium pH value ( pH=10.5) , 20 min deposition can achieve 450 nm film thickness . At lower pH (pH=8.5), low hydrolysis rate of thiourea limits the concentration of sulfur anion , film thickness is only 49 nm after one hour deposition at 70 ¢J , and the obtained thin film can not fully cover the substrate to have a pin-hole free film . At higher pH (pH=11), 40 min only deposites 100 nm film thickness. Strong binding between the cadmium ion and the complexing agent causes low free cadmium cation concentration in the solution, which limits the growing rate. By varying the growth pH condition, the difference in thickness is more than one order of magnitude. In contrast to the film thickness relationship, grain size distribution suffers less influence from the pH consition. Our results indicate no explicitly relation between the grain size and solution pH condition. 20 minutes depositions result cadmium sulfide grain sizes to be 70¡Ó10nm , and 40 minutes result grain size to be 75¡Ó15nm . The results indicate that film thickness increases mainly due to the increasing of grain number, rather than the increasing of grain size . By summarized the results, we propose that the deposition of cadmium sulfide film is initially formed homogeneous nucleation in the solution. The nuclea diffuse and adhere to the substrate. Intristic electric dipole momentum of the cadmium sulfide nano-particle provides an attractive force for the adhesion, and results preferred orientation. Meanwhile, the grain keeps growing up until the size saturated .

Transparent thin film transistors fabricated at room temperature by radio frequency magnetron sputtering using indium oxide material system were proposed. The electrodes of the transparent thin film transistors were obtained by depositing indium oxide with 10% tim doping. Resistivity as low as 4¡Ñ10-4£[-cm at room temperature was achieved. The channel layers of the transparent thin film transistors were fabricated using pure indium oxide target in an Argon and oxygen environment. Resistivity larger than 10-5£[-cm was obtained with 60% oxygen partial pressure. Silicon nitride prepared by room temperature radio frequency sputtering were used for the gate dielectric layer with low leakage current. Environmental-safe lift-off processes were used to fabricated the electrodes, the isolation layer, and the channel layer. The transistor characteristics were obtained by standard I-V measurement. The on-off ratio of the 30£gm ¡Ñ 150£gm transparent thin film transistor is 100.

We attempted to fabricate the CuInSe2:Sb thin-film solar cells with a Al/ZnO:Al(AZO)/ ZnSe /CuInSe2:Sb /Mo/soda-lime glass(SLG) structure. The growth of CuInSe2 film in the presence of Sb can effectively improve the surface morphology and benefit the growth of the device. A ZnSe buffer layer has been applied as an attractive alternative to a CdS buffer layer, thus eliminating environment from pollution. By varying the Ar pressure during the deposition, the Mo bilayer has been fabricated with both low resistivity and good adhesion. Currently the tensile stress was maintained below 100MPa, and the lowest sheet resistance achieved 0.205(£[/¡¼). The fabrication condition with a 5-cm sputtering distance could provide the lowest resistivity of 1.73¡Ñ10-3 (£[-cm) in the AZO thin-film that shows a transmittance of above 80¢Min the visible range. Applying the technology of optical lithography to deposit the Al metal front grid, the Al/ AZO ohmic contact resistance was improved. The energy conversion efficiency of the CIS thin-film solar cell (Al/ AZO/ ZnSe /CuInSe2 /Mo/ SLG) was 4.4¢M(Voc =0.41 V¡AI sc = 3.9 mA ¡AFF = 69 ¢M) by applying the irradiation with a solar simulator under one-sun (AM1.5, 100mW/cm2) conditions. However, the efficiency of CIS:Sb solar cell (Al/ AZO/ ZnSe /CuInSe2 :Sb /Mo/ SLG) was improved to to 6.0¢M(Voc =0.43 V¡AI sc = 5.15 mA ¡AFF = 68 ¢M). This result indicates that the CIS film growth with Sb can increase the short-circuit current.