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Molybdenum (Mo) is a commonly used material as the electrical back contact for Cu(In,Ga)Se2 (CIGS) thin film solar cells taking advantages in electrical, structural and chemical properties. Bilayer structures have been actively examined to achieve Mo films of high conductivity with good substrate adhesion, which will also enable monolithically integrated solar cell modules on flexible platforms by combining laser scribing technology. However, reports on the bilayers on flexible substrates and their scribing by laser are very limited. In this study, we report the characteristics of bilayer Mo films deposited on a flexible polyimide substrate and the impact on the performance of picosecond laser scribing. Bilayer Mo films were deposited over a range of sputtering pressures and discharge powers as well as top-bottom layer thickness ratios, and laser scribing behavior was compared in the practical scribing speed range of the order of m/s. It is shown that microstructural and interfacial characteristics set by top and bottom Mo layers deposition parameters are critical factors influencing laser scribing quality.

A monolithic tandem solar cell consisting of crystalline Si (c-Si)/indium tin oxide (ITO)/CuGaSe2 (CGSe) was demonstrated by stacking a CGSe solar cell on a c-Si/ITO solar cell to obtain a photovoltaic conversion efficiency of about 10%. Electrical analyses based on cell-selective light absorption were applied to individually characterize the photovoltaic performances of the top and bottom subcells. Illumination at a frequency that could be absorbed only by a targeted top or bottom subcell permitted measurement of the open-circuit voltage of the target subcell and the shunt resistance of the non-target subcell. The cell parameters measured from each subcell were very similar to those of the corresponding single cell, confirming the validity of the suggested method. In addition, separating the light absorption intensities at the top and bottom subcells made us measure the bias-dependent photocurrent for each subcell. The series resistance of a c-Si/ITO/CGSe cell subjected to bottom-cell limiting conditions was slightly large, implying that the tunnel junction was a little resistive or slightly beyond ohmic. This analysis demonstrated that aside from producing a slightly resistive tunnel junction, our fabrication processes were successful in monolithically integrating a CGSe cell onto a c-Si/ITO cell without degrading the performances of both cells.

Thin light-active layers of the CuInSe2 solar cell were prepared on Mo-coated sodalime glass substrates by one-step electrodeposition and post-annealing. The structure, morphology, and composition of CuInSe2 film could be controlled by deposition parameters, such as the composition of metallic precursors, the concentration of complexing agents, and the temperature of post-annealing with elemental selenium. A dense and uniform Cu-poor CuInSe2 film was successfully obtained in a range of parametric variation of electrodeposition with a constant voltage of -0.5 V vs. a Ag/AgCl reference electrode. The post-annealing of the film at high temperature above 500℃ induced crystallization of CuInSe2 with well-developed grains. The KCN-treatment of the annealed CuInSe2 films further induced Cu-poor CuInSe2 films without secondary phases, such as Cu2Se. The structure, morphology, and composition of CuInSe2 films were compared with respect to the conditions of electrodeposition and post-annealing using SEM, XRD, Raman, AES and EDS analysis. And the conditions for preparing device-quality CuInSe2 films by electrodeposition were proposed.

Zn-Sn-O (ZTO) films are known to be able to form an amorphous phase, which provides a smooth surface morphology as well as etched side wall, when deposited by using the conventional sputtering technique and, therefore, to have a potential to be applied as transparent thin film transistors. In this study, ZTO thin films were prepared by using combined sputtering of ZnO and SnO2 targets, and the dependences of their electrical and optical properties on the composition and the deposition parameters were examined. The Sn content in the films was varied in the range of 35 ∼ 85 at.%. The deposition was carried out at room temperature, 150 and 300 °C, and the oxygen content in sputtering gas was varied from 0 to 1 vol.%. Sn-rich films had better electrical properties, but showed large oxygen deficiency when deposited at low oxygen partial pressures. ZTO films with Sn contents lower than 55 at.% had good optical transmission, but the electrical properties were poor due to very low carrier concentrations. A high Hall mobility of larger than 10 cm2/Vs could be obtained in the carrier density range 1017∼1020 cm−3, and the etching rate was measurable for films with Sn content up to 70 at.% when using a dilute HCl solution, indicating a good possibility of utilizing ZTO films for device applications.

Formation of abnormal grain inclusions in nanocrystalline diamond films deposited by hot filament CVD (HFCVD) was investigated. The phenomenon was attributed to two different origins: an intrinsic and an extrinsic one. The inclusions due to the intrinsic origin could be either avoided or weakened by controlling chamber pressure, CH4/N2 concentrations in H2, and by positive substrate bias. The extrinsic origin for the abnormal grains was found to be the contamination from the alumina insulation tubes for the thermocouple placed near the substrate, which were degraded by the extended exposure to the high temperature and strongly reducing atmosphere.

The present status of technical development of a highly scalable, high-speed non-volatile PCM is overviewed. Major technical challenges are described along with solutions that are being pursued in terms of innovative device structures and fabrication technologies, new phase change materials, and new memory schemes.

In this study we investigated the oxygen effect on the nucleation and its residual stress during unbalanced magnetron sputtering. Up to 0.5% in oxygen flow rate, cubic phase (c-BN) was dominated with extremely small fraction of Hexagonal phase (h-BN) of increasing trend with oxygen concentration, whereas hexagonal phase is dominated beyond 0.75% flow rate. Interestingly, the residual stress in cubic-phase-dominated films was substantially reduced with small amount of oxygen () down to a low value comparable to the h-BN case. This may be because oxygen atoms break B-N bonds and make B-O bonds more favorably, increasing bonds preference, as revealed by FTIR and NEXAFS. It was confirmed by experimental facts that the threshold bias voltage for nucleation and growth of cubic phase were increased from -55 V to -70 V and from -50 V to -60 V respectively. The reduction of residual stress in O-added c-BN films is seemingly resulting from the microstructure of the films. The oxygen tends to increase slightly the amount of h-BN phase in the grain boundary of c-BN and the soft h-BN phase of 3D network including surrounding nano grains of cubic phase may relax the residual stress of cubic phase.

The cell-to-module efficiency gap in Cu(In,Ga)Se-2 (CIGS) monolithically integrated solar modules is enhanced by contact resistance between the Al-doped ZnO (AZO) and Mo back contact layers, the P2 contact, which connects adjacent cells. The present work evaluated the P2 contact resistance, in addition to the TCO resistance, using an embedded transmission line structure in a commercial-grade module without using special sample fabrication methods. The AZO layers between cells were not scribed; instead, the CIGS/CdS/i-ZnO/AZO device was patterned in a long stripe to permit measurement of the Mo electrode pair resistance over current paths through two P2 contacts (Mo/AZO) and along the AZO layer. The intercept and slope of the resistance as a function of the electrode interval yielded the P2 contact resistance and the TCO resistance, respectively. Calibration of the parasitic resistances is discussed as a method of improving the measurement accuracy. The contribution of the P2 contact resistance to the series resistance was comparable to that of the TCO resistance, and its origin was attributed to remnant MoSe2 phases in the P2 region, as verified by transmission electron microscopy.

Laterally driven microresonators were used to estimate the temperature-dependent elastic modulus of single-crystalline Si for microelectromechanical systems (MEMS). The resonators were fabricated through surface micromachining from silicon-on-glass wafers. They were moved laterally by alternating electrostatic force at a series of frequencies, and then a resonance frequency was determined, under temperature cycling in the range of 25/spl deg/C to 600/spl deg/C, by detecting the maximum displacement. The elastic modulus was obtained in the temperature range by Rayleigh's energy method from the detected resonance frequency. At this time, the temperature dependency of elastic modulus was affected by surface oxidation as well as its intrinsic variation: a temperature cycle permanently reduces the resonance frequency. The effect of Si oxidation was analyzed for thermal cycling by applying a simple composite model to the measured frequency data; here the oxide thickness was estimated from the difference in the resonance frequency before and after the temperature cycle, and was confirmed by field-emission scanning electron microscopy. Finally, the temperature coefficient of the elastic modulus of Si in the direction was determined as -64/spl times/10/sup -6/[/spl deg/C/sup -1/]. This value was quite comparable to those reported in previous literatures, and much more so if the specimen temperature is calibrated more exactly.

The evolution of non-spherical silica particles in a counterflow diffusion flame has been studied considering the effects of convection, diffusion, thermophoresis, chemical reactions, coagulation and coalescence. The counterflow geometry provides a one-dimensional flow field along the stagnation point streamline which greatly simplifies the analysis of non-spherical particle growth. Flame analysis of multi-step chemical reactions of hydrogen/oxygen including both oxidation and hydrolysis of SiCl 4 has been done to predict flame temperatures, concentrations of gas species and particle generation. The present prediction of flame temperatures was in good agreement with the previous experimental data. Two-dimensional aerosol dynamics in which both particle volume and surface area are independent variables has been then analyzed to obtain the evolution of non-spherical particles which has been compared with the previous experimental data. Several different models of coalescence of silica particles were studied; viscous flow sintering, atomistic diffusion sintering, fast sintering and hybrid sintering models. The use of hybrid sintering model yielded the best agreement with the previous experimental data. Since the collision cross section of non-spherical particles is larger than that of spherical particles having the same volume, coagulation of particles was obviously shown to be enhanced. The important role of axial particle diffusion has been identified in the counterflow diffusion flame. Bi-modal size distributions were obtained at some flame heights.

Copper indium gallium selenide (CIGS) absorber thin films were deposited on bilayer Mo back contacts with and without a SiOx film on a soda-lime glass substrate. This was done to control the quantity of alkali metals in the films and to apply the growth method to a substrate that does not contain alkaline elements. The average concentrations of major elements Cu, In, Ga, and Se in the CIGS solar cells were measured by electron probe microanalysis, secondary ion mass spectrometry (SIMS), and Auger electron spectrometry. The SIMS technique was also used to obtain and compare depth profiles of the relative ion intensities of sodium and potassium alkali metals for CIGS thin films with varying cell efficiencies. The CIGS/Mo interfaces also were investigated by transmission electron microscopy (TEM), whereby a cross-sectional view of Mo films prepared with and without an initial SiOx layer made possible the detection of a MoSe2/Mo bilayer with a columnar-type microstructure. Scanning TEM images and correspondin...

By impinging a beam of O+2 ions of energy 150 eV

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A W-band divide-by-3 frequency divider with wide bandwidth and low power dissipation is presented using harmonic injection-locking technique. A cascode FET is employed for a self-oscillating second-harmonic mixer which is injection-locked by third-harmonic input to obtain the division order of three. The fabricated frequency divider using 0.1 μm GaAs metamorphic HEMT technology shows superior performance such as large bandwidth of 6.1 GHz around 83.1 GHz (7.3%) under small DC power consumption of 12 mW.