Change Of RF Power Research Articles

Tailoring of the Structural and Optoelectronic Properties of Zinc-Tin-Oxide Thin Films via Oxygenation Process for Solar Cell Application

In this study, the impact of compositional variation in high resistance transparent (HRT) metal oxide ZTO films of thickness around 100nm has been investigated. The atomic composition in the films has been tailored by the change of RF power and sub-sequent thermal oxygenation in mixed nitrogen and oxygen atmosphere. A phase transition from ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> to ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> was observed in the X-ray diffraction spectra, indicating the possible oxygen incorporation into the films during the thermal annealing process. Uniform microstructures with compact interconnected grains of around 6-7 nm were found in SEM images while no significant changes been observed upon oxygenation. Besides, the significant alteration of electronic properties was noticed as an effect of compositional variation via oxygenation. All the films showed above 85% of optical transmittance in the visible light spectrum. The optimum optoelectronic properties for RF power has been determined as of 50W (ZnO) and 10W (SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) via thermal oxygenation at 400°C where the ratio O/(Zn+Sn) become around 1.6. The significant effect of oxygenation has been realized via primarily fabricated solar cells where the cell with ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> HRT shows higher efficiency than the ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> .

Adjustable Load With Tracking Loop to Improve RF Rectifier Efficiency Under Variable RF Input Power Conditions

Terminating an RF rectifier with an optimum load resistance is important to maximize the efficiency of converting RF power to dc power. The optimum load resistance can also vary significantly as a function of RF input power. Therefore, an adjustable load circuit that tracks changes in RF power is required to maximize efficiency. As a way of implementing an adjustable load circuit that can provide a regulated output voltage to power a host system, a two-stage power-conversion circuit is proposed. The first stage is a dc-to-dc discontinuous mode converter that is controlled by an input loop to regulate the load impedance presented to the RF rectifier. The analysis, design, and experimental results of the first stage adjustable load circuit with a tracking loop are described. The load is connected to a 985-MHz 10-W GaN Class-F RF rectifier and results with the load circuit are compared to the optimum load.

결정질 실리콘 태양전지를 위한 실리콘 질화막의 특성

Silicon nitride() deposited by radio frequency plasma enhanced chemical vapor deposition(RF-PECVD) is commonly used for anti-reflection coating and passivation in crystalline silicon solar cell fabrication. In this paper, characteristics of the deposited silicon nitride was studied with change of working pressure, deposition temperature, gas ratio of and , and RF power during deposition. The deposition rate, refractive index and effective lifetime were analyzed. The (100) p-type silicon wafers with one-side polished, , and resistivity were used. As a result, when the working pressure increased, the deposition rate of SiNx was increased while the effective life time for the -deposited wafer was decreased. The result regarding deposition temperature, gas ratio and RF power changes would be explained in detail below. In this paper, the optimized condition in silicon nitride deposition for silicon solar cell was obtained as 1.0 Torr for the working pressure, for deposition temperature, 500 W for RF power and 0.88 for gas ratio. The silicon nitride layer deposited in this condition showed the effective life time of > and the surface recombination rate of 25 cm/s. The crystalline silicon solar cell fabricated with this SiNx coating showed 18.1% conversion efficiency.

RF 파워에 따라 스퍼터된 Al doped ZnO 박막의 구조적, 광학적, 전기적 특성

We have studied structural, optical, and electrical properties of the Al-doped ZnO (AZO) thin films being usable in transparent conducting oxides. The AZO thin films were deposited on the corning 1737 glass plate by the RF magnetron sputtering system. To find optimal properties of AZO for transparent conducting oxides, the RF power in sputtering process was varied as 40 W, 60 W, and 80 W, respectively. As RF power increased, the crystallinity of AZO thin film was decreased, the optical bandgap of AZO thin film increased. The transmittance of the film was over 80% in the visible light range regardless of the changes in RF power. The measurement of Hall effect characterizes the whole thin film as n-type, and the electrical property was improved with increasing RF power. The structural, optical, and electrical properties of the AZO thin films were affected by Al dopant content in AZO thin film.

Nanocrystallites formation in a‐SiC by low power plasma enhanced chemical vapour deposition

AbstractFormation of nanocrystallites in the amorphous silicon carbide thin films deposited from silane methane mixture diluted in argon by plasma enhanced CVD has been studied under different levels of rf power density and Ar dilution. Systematic transformations between different polymorphic phases of SiC have been observed with changes in rf power and Ar dilution. At low Ar dilution no H‐SiC (α‐SiC) nanocrystallites was observed. Only traces of β‐SiC of Si were observed. With increase in Ar dilution formation of α‐SiC nanocrystallites was observed. Increase of rf power density at this dilution enhanced α‐SiC nanocrystallites but reduced β‐SiC slightly. Variation of SiC peak in the infra red absorption corresponds closely with the changes in β‐SiC nanocrystallites in the layers. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei

Various amplitude- and phase-modulated excitation pulses for the observation of static NMR powder patterns from half-integer quadrupolar nuclei have been generated using the optimal control routines implemented in SIMPSON 2.0. Such pulses are capable of both excitation of the central transition and signal enhancement by population transfer from the satellites. Enhancements in excess of 100% have been achieved for the central transition of the spin-3/2 87Rb nucleus compared with a selective π/2 pulse. These pulses are shown to be relatively insensitive to changes in RF power and transmitter offsets, and can achieve a more uniform signal enhancement than double-frequency sweeps (DFS), resulting in more accurate spectral lineshapes. We also investigate the possibility of “calibration-free” optimized pulses for general use on half-integer quadrupoles with unknown interaction parameters. Such pulses could prove extremely useful for studying low abundance or insensitive nuclei for which experimental optimization of the DFS scheme may be difficult. We demonstrate that a pulse optimized for an arbitrary spin-3/2 system can function well on multiple samples, and can also excite the central transition of higher spin numbers, albeit with a smaller enhancement. The mechanism by which these optimized pulses achieve the signal enhancement is highly complex and, unlike DFS, involves a non-linear excitation of the satellite transition manifold, as well as the generation and manipulation of significant multiple-quantum coherences.

Effects of low-temperature-buffer, rf-power, and annealing on structural and optical properties of ZnO/Al2O3(0001) thin films grown by rf-magnetron sputtering

ZnO thin films were epitaxially grown on Al2O3 (0001) substrates in a radio-frequency (rf) magnetron sputtering chamber. The surface morphology of ZnO was remarkably affected by the incorporation of a low-temperature grown ZnO buffer as well as the changes in rf-power. X-ray diffractions, combined with the surface micropits, revealed strain relaxations in the ZnO epilayers grown with higher rf-powers, which in turn caused a redshift to the intrinsic exciton absorption peak. Strain relaxations were also observed in the ZnO epilayers upon thermal annealing, which led to a redshift in the E2high Raman mode. A factor of ∼0.7 cm−1 GPa−1, i.e., a biaxial stress of 1 GPa can shift the E2high mode by 0.7 cm−1, was obtained. The point defects related absorptions and the exciton localizations were suppressed by annealing, which, in conjunction with the strain-relaxation induced redshift in the intrinsic-exciton absorptions, steepened the absorption edge and increased the optical bandgap energy of the ZnO epilayer.

Drag coefficient of the weakly ionized plasma in the high Knudsen number regime

The drag force acting on a micron-sized polystyrene particle in the high Knudsen number regime is investigated. Analysis of the particle trajectories in stationary neutral argon gas environment suggests the damping time constant τ∝p−1.20±0.04 and Epstein drag force coefficient δ=1.40. The neutral drag coefficient is compared with the drag coefficient measurement in dust-free plasma. The phenomena of the reduced drag in weakly viscous and weakly ionized rf plasma are also observed in this report. It is shown that the slight changes in rf power and pressure would enhance the reduced drag effect, which suggests that there is an additional electrostatic force acting along the particle motion in the plasma.

Effects of rf power on electron density and temperature, neutral temperature, and Te fluctuations in an inductively coupled plasma

Atomic clocks that fly on global-navigation satellites such as global positioning system (GPS) and Galileo employ light from low-temperature, inductively coupled plasmas (ICPs) for atomic signal generation and detection (i.e., alkali/noble-gas rf-discharge lamps). In this application, the performance of the atomic clock and the capabilities of the navigation system depend sensitively on the stability of the ICP’s optical emission. In order to better understand the mechanisms that might lead to instability in these rf-discharge lamps, and hence the satellite atomic clocks, we studied the optical emission from a Rb/Xe ICP as a function of the rf power driving the plasma. Surprisingly, we found that the electron density in the plasma was essentially independent of increases in rf power above its nominal value (i.e., “rf-power gain”) and that the electron temperature was only a slowly varying function of rf-power gain. The primary effect of rf power was to increase the temperature of the neutrals in the plasma, which was manifested by an increase in Rb vapor density. Interestingly, we also found evidence for electron temperature fluctuations (i.e., fluctuations in the plasma’s high-energy electron content). The variance of these fluctuations scaled inversely with the plasma’s mean electron temperature and was consistent with a simple model that assumed that the total electron density in the discharge was independent of rf power. Taken as a whole, our results indicate that the electrons in alkali/noble-gas ICPs are little affected by slight changes in rf power and that the primary effect of such changes is to heat the plasma’s neutral species.

Actinometry of inductively coupled Cl2∕N2 plasmas for dry etching of GaAs

Inductively coupled plasma dry etching of GaAs with Cl2∕N2-containing plasmas and investigations of these plasmas with optical emission spectroscopy and actinometry are presented. The results of actinometry were revised to allow the comparison of relative ground-state densities at different pressures. The obtained relative ground-state densities of N2, Cl2, and Cl (I) are presented as functions of the process parameters [rf power, pressure, and Cl2∕(Cl2+N2) ratio]. Cl (I) relative ground-state densities were found to be linearly connected to the pressure and the Cl2∕(Cl2+N2) ratio. GaAs etch rates up to 3μm∕min were obtained, while etch rates of the photoresist mask did not exceed 0.95μm∕min. The impact of the rf power changes on the etch rates was negligible. Plotting the etch rates against the process parameters revealed a linear relationship between the etch rates and the pressure and between the etch rates and the Cl2∕(Cl2+N2) ratio. Therefore a correlation between the Cl (I) relative ground-state density measured in plasmas without wafer and GaAs and the photoresist mask etch rate was found. All GaAs dry etching examined in this investigation was found to take place in a reactant-limited regime with Cl (I) as the rate-limiting species.

Effect of hydrogen radicals on properties and structure of a-Si1−xCx:H films

We investigated the effect of hydrogen radicals on properties and structure of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films by the use of a preparation system possessing both hydrogen plasma chamber and silane/methane plasma chamber. The deposition rate, the carbon content, the optical band gap and the film structure investigated with IR transmission spectroscopy remained unchanged with changes in rf power on the hydrogen plasma side. However, the refractive index increased with increasing the rf power on the hydrogen plasma side. The Urbach energy decreased from 67 to 53 meV. The photoconductivity of the films prepared with the rf power on the hydrogen plasma side of 100 W was improved to be 3×10−5 S cm−1, which was by about two orders of the magnitude larger than that without hydrogen plasma. For preparing photoconductive a-Si1−xCx:H films, it is important to generate a number of hydrogen radicals and introduce them onto the growing film surface efficiently.

Formation of 6H–SiC due to subsequent annealing of sputtering a-SiC:H films

In this paper, the phase formation of 6H–SiC is studied through a 60 min isochronal annealing of a-SiC:H prepared at the substrate temperature of about 100°C by reactive rf sputtering. Infrared transmission, Raman scattering and X-ray diffraction analyses are employed to characterize the films before and after annealing. It shows that a-SiC:H deposited at higher rf power changes into 6H–SiC phase, along with the disappearance of silicon or carbon clusters existed in as-prepared films, at annealing temperature of 800°C, while 1000°C is required for the phase change of those deposited at lower rf power. It is suggested that the bombardment of energetic argon ions during deposition is responsible for the enhancement of 6H–SiC formation, decrease of hydrogen content, and homogeneity of the films.

Ca and Na interference effects in an axially viewed ICP using low and high aerosol loadings

Ca and Na interference effects in an axially viewed inductively coupled plasma using low and high aerosol loadings were compared for a wide range of spectral lines differing in energy potentials. A simultaneous multichannel segmented charge coupled device atomic emission spectrometer was employed. Limits of detection for aqueous solutions and solutions containing 0.1% Ca and Na were determined. In comparison with the limits of detection using a cross-flow nebulizer, the mean improvement for a pure aqueous solution using an ultrasonic nebulizer was about 10-fold. However, relative to an aqueous solution, detection limits in 0.1% Na and Ca were degraded 16-10-fold for the cross-flow nebulizer and about 30-fold for the ultrasonic nebulizer. In the presence of Na and Ca at 1.35 kW, most spectral lines studied were depressed by up to 10 and 20%, respectively, using a cross-flow nebulizer. With an ultrasonic nebulizer, matrix effects were larger and both intensity enhancement and attenuation were observed, ±20-30% for Na and ±30-50% for Ca. The intensities of high energy lines were attenuated to a larger extent, whereas those for very low energy lines were enhanced, particularly in the presence of Ca. Matrix effects were reduced by up to 30% when the rf power was increased from 1 to 1.35 kW. The Mg II 280.270/Mg I 285.213 nm intensity ratio was employed to compare plasma robustness in response to high Ca and Na concentrations, mode of sample introduction and rf power changes. Ratios increased when the power was increased, but decreased when Ca and Na were present in the aspirated solutions. When the power was increased, plasma robustness increased by 20-40% when a cross-flow nebulizer was employed and 50% when the ultrasonic nebulizer was used. It was concluded that high rf power is favorable for the analysis of environmental materials.

Effect of radio-frequency power and substrate temperature on properties of hot-plasma-box glow-discharge-deposited hydrogenated amorphous silicon carbon alloys

The effect of rf power and substrate temperature Ts on the optical, electrical, and structural properties of a-Si1−xCx:H alloy films deposited in the new hot-plasma-box glow-discharge reactor are reported. The rate of deposition as well as the total fraction x of the carbon incorporated in the alloy films were found to vary in a direct proportion with the rf power, whereas the same parameters displayed an inverse proportionality to the changes in Ts. Second, the hydrogen concentration in the alloy films was found to decrease with the increase in substrate temperature while it did not show appreciable variation with the changes in rf power. Next, the structural disorder in the amorphous network was observed to increase rapidly with increase in rf power although a slight improvement was made possible by elevating the Ts. The analysis of Raman scattering and optical band-gap measurements on these alloy films indicates that a large proportion of the Si—C and C—C bond pairs favors the diamondlike (sp3) bonding configuration at low rf power when the Ts is high, whereas the graphitelike (sp2) C—C clusters show up only at high rf power values when the Ts is low. The efficiency of C incorporation in these alloy films prepared by the present technique appears to be better than its best possible magnitude in the conventional open parallel-plate glow-discharge-deposition systems.

Principal Component Analysis of Optical Emission Spectroscopy and Mass Spectrometry: Application to Reactive Ion Etch Process Parameter Estimation Using Neural Networks

We report on a simple technique that characterizes the effect of process parameters (i.e., pressure, RF power, and gas mixture) on the optical emission and mass spectra of plasma. This technique is sensitive to changes in chamber contamination levels (e.g., formation of Teflon‐like thin‐film), and appears to be a promising tool for real‐time monitoring and control of reactive ion etching. Through principal component analysis, we observe that 99% of the variance in the more than 1100 optical and mass spectra channels are accounted for by the first four principal components of each sensor. Projection of the mass spectrum on its principal components suggests a strong linear relationship with respect to chamber pressure. This representation also shows that the effect of changes in thin‐film levels, gas mixture, and RF power on the mass spectrum is complicated, but predictable. To model the nonlinear relationship between these process parameters and the principal component projections, a feedforward, multi‐layered neural network is trained and is shown to be able to predict all process parameters from either the mass or the optical spectrum. The projections of the optical emission spectrum on its principal components suggest that optical emission spectroscopy is much more sensitive to changes in RF power than the mass spectrum, as measured by the residual gas analyzer. Model performance can be significantly improved if both the optical and mass spectrum projections are used (so called sensor fusion). Our analysis indicates that accurate estimates of process parameters and chamber conditions can be made with relatively simple neural network models which fuse the principal components of the measured optical emission and mass spectra.

Novel method of dro frequency tuning with varactor diode

A novel method of electrical frequency tuning for a dielectric resonator oscillator is presented. The idea is to place an opened λ/4 line, with a varactor diode at one end, onto the screw for frequency tuning which is above the dielectric resonator. The central frequency offset achieved with the DRO realised at 14 GHz was 4 MHz, while the change of RF power was less than 0.5 dBm.

Application of Emission Spectroscopy for Profile Control during Oxygen RIE of Thick Photoresist

Oxygen reactive ion etching of the planarizing photoresist layer in a three‐layer resist system is described. The vertical and lateral etch rates of the thick resist layer, as well as the degree of isotropy of the resist profile, are reported as functions of RF power and oxygen pressure. The optical emission spectra are recorded and interpreted for oxygen plasmas used in etching, revealing the presence of oxygen atoms (O) and ionized oxygen molecules . It is demonstrated that trends in the degree of isotropy which occur with changes in RF power and oxygen pressure can be predicted by monitoring the emission intensity ratio.

Some Properties of Intrinsic and Phosphorus Doped Amorphous Silicon Thin Films

The dark conductivity σD and the photoconductivity σPh of intrinsic and n-type (phosphorus doped) a-Si: H films prepared by rf glow discharge of silane gas has been studied. The samples have been prepared under different experimental conditions which include change of rf power, substrate temperature and dopant concentration. The most significant result has been the change in dark conductivity and photoconductivity with the change of rf power within a limited range of 2 to 30 Watts. As shown by infrared spectroscopy the chances in σD and σPh with rf power are mainly due to the change of hydrogen content. The appearance of a kink in σD vs 1/T plot (at T' with higher slope at T>T') has been explained as due to the effect of statistical shift of the Fermi level EF.

Microwave-Induced Plasma Shield Propagation in Rare Gases

It has been observed that microwave irradiation of localized weak ionization in heavy rare gases can cause an ionization wave (“plasma shield”) to form and propagate toward the rf source. This ionization wave is preceded by an electron precursor, with the electron density at the ionization wave front increasing very rapidly to a maximum followed by a relatively slow plasma decay. At rf power levels well below normal breakdown, the ionization wave will form and then propagate at velocities from about 2 × 103 cm/sec to 1 × 107 cm/sec. Discontinuous changes of ionization wave velocities with changes in rf power and gas pressure indicate the existence of three different velocity-controlling mechanisms in the gas pressure and rf power ranges investigated. These mechanisms for ionization wave formation and propagation have been investigated in xenon, krypton, and argon gases, and are discussed.