Very High Frequency Plasma Enhanced Chemical Vapor Deposition Research Articles

Effect of a-SiCxNy:H Encapsulation on the Stability and Photoluminescence Property of CsPbBr3 Quantum Dots.

The effect of a-SiCxNy:H encapsulation layers, which are prepared using the very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with SiH4, CH4, and NH3 as the precursors, on the stability and photoluminescence of CsPbBr3 quantum dots (QDs) were investigated in this study. The results show that a-SiCxNy:H encapsulation layers containing a high N content of approximately 50% cause severe PL degradation of CsPbBr3 QDs. However, by reducing the N content in the a-SiCxNy:H layer, the PL degradation of CsPbBr3 QDs can be significantly minimized. As the N content decreases from around 50% to 26%, the dominant phase in the a-SiCxNy:H layer changes from SiNx to SiCxNy. This transition preserves the inherent PL characteristics of CsPbBr3 QDs, while also providing them with long-term stability when exposed to air, high temperatures (205 °C), and UV illumination for over 600 days. This method provided an effective and practical approach to enhance the stability and PL characteristics of CsPbBr3 QD thin films, thus holding potential for future developments in optoelectronic devices.

High-Quality Nanocrystalline Silicon (nc-Si:H) Thin Film With Mixed-Phase and Its Application of Circulating Tumor Cell DEP Biochip

This paper proposes the light-induced dielectrophoresis (DEP) biochip prepared by 40.68-MHz very high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) and post- microwave annealing treatment. The biochip can screen circulating tumor cells without using any antibodies and biomarkers. Therefore, the biochip’s high efficiency and high purity are goals for effectively conducting the whole genome sequencing (WGS) analysis. The quality, uniformity, and electrical properties of the prepared silicon thin films affect the performance parameters of the biochip. High-quality nanocrystalline silicon (nc-Si:H) thin film is the core technology in the biochip. High-density nc-Si:H thin films can be well prepared using 40.68 MHz VHFPECVD and post-treatment microwave annealing. Microwave annealing improves the crystallinity and reduces the defects in the nc-Si:H thin films discovered by Fourier-transform infrared spectroscopy (FTIR). The prepared thin film with a crystallinity of 5% enhanced 38.3%, surface roughness of 10.93 nm, and a photo/dark current of 7.1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> with a power density of 60mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was obtained. The biochip showed a recovery rate of 81.3%, purity of 78.6%, and survival rate of 91% for applying to the circulating tumor cells (CTCs).

Dynamic deposition system for fabrication of amorphous/crystalline silicon heterojunction solar cells combining linear hot-wire and plasma enhanced chemical vapor deposition methods.

In this work an integration of two in-line deposition methods consisting of a linear hot-wire (HW) and very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) into a single in-line system for the fabrication process of highly efficient heterojunction solar cells was demonstrated. Using this continuous deposition methods, which are also well suited for roll-to-roll production, a high productivity can be achieved. In principle, the up-scaling of the electrode width is possible and no severe deterioration of the uniformity of the deposited layers is expected. With the linear configuration the homogeneity of the layer deposition has to be ensured in only one dimension (perpendicular to the movement direction of the substrate). The homogeneity in the second dimension is realized by the movement of the substrate at constant speed, thus the homogeneous deposition even on large area substrates is possible. In this work the individual steps for development of the passivation process using different in-line deposition methods were investigated. The results show that dynamic HW- and VH-PECVD technologies enables fabrication of the layers with high deposition rates and high passivation properties (carrier lifetimes > 13 ms) as well as highly efficient solar cells (efficiency > 22%).

Effects of Chamber Pressures on the Passivation Layer of Hydrogenated Nano-Crystalline Silicon Mixed-Phase Thin Film by Using Microwave Annealing

This paper proposes the effects of chamber pressures on the passivation layer of hydrogenated nano-crystalline silicon (nc-Si:H) mixed-phase thin film using microwave annealing (MWA) to achieve a high-quality thin film. The use of 40.68 MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) deposited the nc-Si:H mixed-phase thin film on the top and bottom of the n-type crystalline silicon substrate. The chamber pressures (0.2, 0.4, 0.6, and 0.8 Torr) of the VHFPECVD were critical factors in controlling the carrier lifetime of the symmetric structure. By using the VHFPECVD to deposit the nc-Si:H and using the MWA to enhance the quality of the symmetric structure, the deposited nc-Si:H’s properties of a crystalline volume fraction of 29.6%, an optical bandgap of 1.744 eV, and a carrier lifetime of 2942.36 μs were well achieved, and could be valuable in thin-film solar-cell applications.

High-Efficiency Light-Induced Circulating Tumor Cells Screening Biochip Prepared by 40.68-MHz VHFPECVD

A high-efficiency biochip for screening circulating tumor cells is proposed by using circulating tumor cells screening biochip using the nanocrystalline silicon (nc-Si:H) thin film prepared by 40.68-MHz very high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) is proposed. The quality, uniformity, and electrical properties of the prepared nc-Si:H thin films affect the performance parameters of the biochip, such as its recovery rate, purity, and survival rate, for screening circulating tumor cells. By applying different chamber pressures of 600, 800, and 1000 mTorr, during 40.68-MHz VHFPECVD, the high-quality nc-Si:H thin film with a surface roughness of 10.9 nm, a resistivity of $3.3\times 10^{1} \Omega $ -cm, and an absorption coefficient of 104 cm −1 was obtained. The proposed circulating tumor cells screening biochip exhibited a recovery rate of 76%, purity of 82%, and survival rate of 88%. The screening performance of the biochip is highly associated with the quality of the deposited nc-Si:H thin films; therefore, the selection of an appropriate deposition technique is crucial for applications in a clinical trial.

Structural and Photoluminescence Properties of nc-SiOx:H/a-SiOx:H Multilayer Films Deposited at Low Temperature by VHF-PECVD Technique

Hydrogenated nanocrystalline silicon oxide/hydrogenated amorphous silicon oxide (nc-SiOx:H/a-SiOx:H) multilayer films were fabricated using very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique by alternate deposition of nc-SiOx:H and a-SiOx:H at a low substrate temperature of 220 °C. The effects of the amount of oxygen incorporation in the nc-SiOx:H sublayers on the structural and photoluminescence (PL) properties of nc-SiOx:H/a-SiOx:H multilayer films were investigated by transmission electron microscopy, Raman scattering, UV–VIS-NIR absorption spectra, steady and time-resolved PL spectra. As the amount of oxygen incorporation increases, the crystalline volume fraction of multilayer films decreases, while the intermediate-range order of multilayer films firstly increases and then decreases. Strong room temperature PL has been observed in the multilayer films and the correlation between structural and PL properties is discussed. This low-temperature procedure for fabricating nc-SiOx:H/a-SiOx:H multilayer films can provide powerful impetus for the further development of optoelectronic devices based on Si-NCs.

Effect of deposition rate on the growth mechanism of microcrystalline silicon thin films using very high frequency PECVD

The intrinsic microcrystalline silicon thin films were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Two series of films with different deposition rate 0.30 nm/s and 1.94 nm/s were prepared. The film surface and gas phase reaction growth processes were monitored with real-time spectroscopic ellipsometry and optical emission spectroscopy. The effect of deposition rate on the microcrystalline silicon thin film growth mechanism has been studied. The microcrystalline silicon surface growth was analyzed with KPZ model. The results show that the growth exponent of β is 0.448 for the films with low deposition rate, and the growth exponent of β is 0.302 for the films with high deposition rate. The growth exponent does not increase with deposition rate, but declines. And the reasons for this phenomenon were explained.

A comparative study of nanocrystalline SiC thin films on multimode optical fiber sensors, synthesized via DBD-NTP and 150 MHz VHF-PECVD

In this study, nanocrystalline SiC films were successfully synthesized on the surface of multimode fiber (MMF) sensors using 150MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) and dielectric barrier discharge nonthermal plasma (DBD-NTP) methods. The effects of the different utilized methods and various deposition times on the microstructure and chemical composition of the deposited SiC films were investigated For both methods, the SiC film thickness increased with increased deposition time. The dependency of sensitivity on the deposition time and thickness of SiC films was studied by investigating the effects of refractive index and temperature variation on the response of the MMF sensors. The SiC films deposited by 150MHz VHF-PECVD showed more uniformity and higher sensitivity compared to those deposited using DBD-NTP. Using VHF-PECVD with a deposition time of 1min yielded the lowest thickness (54.06nm) and therefore the highest sensitivity (0.0240dB/°C) for the SiC-deposited MMF sensors. Thus, the VHF-PECVD method may be a better option than DBD-NTP for the deposition of thin SiC films to improve the sensitivity of the MMF sensors.

Spectroscopic ellipsometry investigation of microcrystalline fractions in p-type hydrogenated microcrystalline silicon oxide (p-μc-SiOx:H) ultra-thin films

Spectroscopic ellipsometry (SE) was used to characterize the effect of the CO2/SiH4 ratios on the p-type hydrogenated microcrystalline silicon oxide (p-μc-SiOx:H) thin films. The p-μc-SiOx:H thin films were fabricated by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) method on the soda-lime glass substrates. The CO2/SiH4 ratios were varied from 0.0 to 0.5 with constant H2-dilution during the deposition. The p-μc-SiOx:H samples were analyzed for thickness, microstructure, and optical characteristics by SE. The ellipsometric measurements were performed in the range of 0.75–5.5eV with the incident angle of 50, 60 and 70 degrees. The physical structures were proposed as either the double- and triple-layer models. The optical dispersion was proposed based on Tauc-Lorentz (TL) model in order to extract the information of interest including dielectric dispersion and crystalline fraction. The results from the SE analyses showed that the thin films prepared with pure SiH4 could only be fitted by the triple-layer model, whose effect refractive index was gradually decreased from 3.92 to 2.53 with the increased CO2/SiH4 ratio. With the introduction of the CO2, the obtained films were instead best represented by the double-layer model. The calculated crystalline fractions could be determined from the SE results, which accurately corresponded to those from the Raman spectroscopy and high-resolution transmission electron microscope (HRTEM). In addition, the dielectric dispersion of the thin films was related directly with CO2/SiH4 ratios, but inversely with crystalline fraction with the values of 53 down to 18% with the increased gas mixture ratio.

Pressure dependent tailored attributes of silicon nanoneedles grown by VHF plasma technique

Gold (Au) catalysts assisted well-aligned silicon nanoneedles (SiNNs) are synthesized using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The tailored morphology and the optical reflectance of such NNs are inspected as a function of varying reactor pressure (200–800 mTorr). FESEM images revealed the growth of high density SiNNs with diameter ranging from 45 to 600 nm and length as much as 5.66 ± 0.2 μm. Overall morphology of these NNs are found to be highly sensitive to the pressure variation, where appreciably aligned thinner NNs are achieved at 600 mTorr pressure. The presence of globule at the NNs tip authenticated their VLS mechanism mediated growth. The reactor pressure sensitivity of the aspect ratio, lattice parameters, Raman modes, and reflectance are demonstrated. XRD patterns manifested SiNNs cubic crystalline phase with preferred orientation along 〈111〉 direction. The occurrence of NNs high crystallinity is further supported by the Raman and HRTEM data. The reflectance of SiNNs grown at 600 mTorr exhibited remarkable reduction (∼6.3%) than those obtained at other pressures. This reactor pressure dependent significant modification in the physical properties of synthesized SiNNs may be prospective for the development of optoelectronics.

Structural and optoelectronic characteristics of nanocrystalline silicon oxide film as absorber layer for thin film solar cells

The mixed phase nanocrystalline silicon oxide (nc-SiOx:H) thin films have been prepared by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) system from SiH4, H2 and CO2 mixture. The effect of oxygen incorporation on the structural and opto-electrical properties of nc-Si:H films was investigated. As the CO2 flow rate increased, the crystalline volume fraction in the films decreased, while the optical band gap increased slowly. During the phase transition, both oxygen and hydrogen content increased drastically with the increasing CO2 flow rate, while the Urbatch energy and microstructure factor showed obvious reduction, which indicated an enhancement of the medium range order of the films and good passivation of the inner voids. Device quality nc-SiOx:H film was fabricated with low microstructure factor of 0.32 and high crystalline volume fraction around 50%, along with wide optical band gap of ∼1.75 eV, low dark-conductivity σd ∼7.6 × 10−6 S/cm and high photosensitivity of about 2 × 102. On flat substrate a solar cell was prepared with high Voc of 0.62 V and Jsc of 14.57 mA/cm2. These results revealed the potential of nc-SiOx:H film as an absorber layer for thin film solar cells.

Extraction of the defect density of states in microcrystalline silicon from experimental results and simulation studies

The constant photocurrent method in the ac-mode (ac-CPM) is used to determine the defect density of states (DOS) in hydrogenated microcrystalline silicon (μc-Si:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD). The absorption coefficient spectrum (ac-α(hv)), is measured under ac-CPM conditions at 60 Hz. The measured ac-α(hv) is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α(hv) in the present work and a previously measured transient photocurrent (TPC) for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α(hv) is found to agree satisfactorily with the measured ac-α(hv).

Effect of thermal annealing on the blue luminescence of amorphous silicon oxycarbide films

Amorphous silicon oxycarbide (a-SiCxOy) films that displayed blue luminescence were fabricated using very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) at a temperature of 250°C. The effects of thermal annealing on the photoluminescence (PL) were investigated. Thermal annealing at 600°C resulted in a remarkable enhancement in the blue PL, which was clearly observed with the naked eyes in a bright room. The blue PL featured an excitation wavelength independent recombination dynamic on a nanosecond timescale. Neither Si nor SiC quantum dots were present in the annealed films as revealed by transmission electron microscopy. The PL results, combined with an analysis of the chemical bonds present in the films, revealed that the origin of the blue PL was largely due to electron–hole pair recombination through Si-related neutral oxygen vacancy defect centers.

High efficiency a-Si:H/a-SiGe:H tandem solar cells fabricated with the combination of V- and U-shaped band gap profiling techniques

Hydrogenated amorphous silicon germanium (a-SiGe:H) films prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) using a mixture of SiH4, H2, and GeH4 were investigated for their use as the bottom cell of amorphous silicon/amorphous silicon germanium (a-Si:H/a-SiGe:H) tandem solar cell structures. Narrow optical band gaps (Eopt) in the range of 1.5 to 1.6 eV were obtained by varying the GeH4/(SiH4 + GeH4) gas flow rate ratio in low-temperature deposition. The a-SiGe:H films deposited with various GeH4/(SiH4 + GeH4) gas flow rate ratios were used as intrinsic layers for the a-Si:H/a-SiGe:H tandem solar cells with different graded band gaps: V-, VU-, and U-shapes. It was found that using the VU-shape improves the solar cell efficiency owing to a higher Jsc when compared with using V-shape. The VU-shape’s Voc and FF are also improved when compared with the U-shape’s Voc and FF. As a result, a high efficiency of 11.0% (Voc = 1.74 V, Jsc = 9.07 mA/cm2, and FF = 0.70) was successfully achieved with the solar cells fabricated using the VU-shape graded band gap technique.

Improved structural features of Au-catalyzed silicon nanoneedles

Nanometer sized silicon (Si) needles (nanowires) offer a vehicle for varieties of applications at nanoscale. We grow Si nanoneedles (SiNNs) using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method with distinct gold (Au) nanostructures (NSs) as catalyst. Au NSs in the form of nanoparticles (NPs) and continuous thin film are prepared on Si(100) substrates via radio frequency magnetron sputtering. Au catalyst size dependent surface morphology and structural features of these SiNNs are determined. Samples are characterized via imaging and spectroscopic measurements. Controlled growth of such SiNNs structure with reproducibility that is achieved via Au NPs size tunability is attributed to the vapor–liquid–solid (VLS) growth mechanism. SiNNs with diameters between 20 and 120nm and length up to 5μm are acquired. SiNNs diameter is found to increase with the increase of Au NPs size. Processing parameters optimization is demonstrated to play a critical role in nucleating Au NPs and thereby achieving high density SiNNs morphology. X-ray diffraction patterns authenticated an enhanced SiNNs crystallinity with increasing catalyst size. Raman spectra of SiNNs revealed a red-shift (∼8.26cm−1) in the first-order transversal band as the average diameter of NNs are decrease from 69 to 57nm. Our systematic method for synthesis and characterization may contribute toward the development of SiNNs based optoelectronics.

High-efficiency microcrystalline silicon solar cells on honeycomb textured substrates grown with high-rate VHF plasma-enhanced chemical vapor deposition

The potential of high-rate growth of high-quality microcrystalline silicon (µc-Si:H) films for solar cell applications is investigated by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) under a high-pressure SiH4 depletion condition. It is found that the morphology of textured substrates plays an important role in not only light trapping but also µc-Si:H film growth. A high conversion efficiency of 11.1% is attained in a substrate-type µc-Si:H cell on a substrate with honeycomb textures, which has rounded concaves in a honeycomb arrangement with an appropriate period. It is also clarified that ZnO:B films grown by metal organic chemical vapor deposition (MOCVD) are beneficial in terms of carrier collection compared with the standard In2O3:Sn (ITO) film grown by sputtering. On the basis of these findings, a new world-record µc-Si:H cell with a certified conversion efficiency of 11.8% is developed with a relatively high deposition rate of 1 nm/s.

Investigation of structural disorder using electron temperature in VHF-PECVD on hydrogenated amorphous silicon films for thin film solar cell applications.

Electrode distances and gas flow ratios are important parameters for fabricating intrinsic (i-type) layers of hydrogenated amorphous silicon (a-Si:H) films using a very high frequency plasma-enhanced chemical-vapor deposition (VHF-PECVD) system. In this work, we investigated the relationship between the electrode distances and gas flow ratios on the properties of i-type a-Si:H films. The electrical, chemical and structural properties are improved with decreasing electrode distances (20-40 mm) at a hydrogen ratio [R (H2/SiH4) = 4], due to the low electron temperature and heating effect. A low electron temperature generates silane-related-reactive species (SiH3) and decreases structural disorder resulting in high quality i-type a-Si:H films. The electrical, chemical and structural properties of the a-Si:H films are confirmed using Al coplanar electrodes, FTIR, Raman spectroscopy, and spectroscopy ellipsometry (SE). When a solar cell is fabricated using the a-Si:H film, J(sc) of 13.2-14.8 mA/cm2, photoconductivity of 1.5 x 10(-5)-8.6 x 10(-6) S/cm, Si--H2 content of 0-1.24 at.%, and hydrogen content of about 10 at.% are obtained. These results together with a model of the plasma chemistry indicate that H atoms and SiH3 radicals play an important role in the deposition process.

Control of micro void fraction and optical band gap in intrinsic amorphous silicon thin films (VHF-PECVD) for thin film solar cell application

Plasma parameters are important factors for fabricating intrinsic (i-type) layers of hydrogenated amorphous silicon (a-Si:H) films using a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) system. In this work, the effects of hydrogen ratio (R), power density, pressure, electrode instances (Ed) and substrate temperature (Ts) on the growth and the properties of intrinsic amorphous silicon (i-type a-Si:H) thin films are investigated. The structural defect (micro void fraction: R*) and optical band gap (Eg) can be controlled by changing the plasma conditions. High quality i-type a-Si:H is obtained with low power, pressure, moderate hydrogen ratio (R&9552;H2/SiH4: 4) and short electrode distance conditions at which a lot of SiH3 radicals are generated. When the substrate temperate is above 200°C, hydrogen effusion decreases SiH bonding and optical band gap of 1.74eV is obtained.The properties of i-type a-Si:H depending on plasma conditions show hydrogen content (C(H))=6–11%, R*=0–0.2 and Eg=1.74–1.86eV. The properties of region of low structural defect and good passivation represent C(H)=about 10 at.%, R*=0 and Eg=1.77eV.

Vertically-tapered silicon nanowire arrays prepared by plasma enhanced chemical vapor deposition: Synthesis, structural characterization and photoluminescence

Vertically aligned silicon nanowires (SiNWs) have been successfully synthesized using pure silane gas as a precursor by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The effect of the growth temperature on the morphology, structure and photoluminescence properties of SiNWs has been studied. The SiNWs were needle-liked materials with the length of a few microns having the diameters of tens of nanometers near the bottom and a few nanometers at the top. Thinner nanowires have been obtained at the higher growth temperature process. High resolution transmission electron microscopy confirms that the nanowires are composed of a crystalline silicon core with an oxide shell. The PL spectrum of the Si nanoneedles have shown two emission bands around 450nm and ~750, which originate from the defects related to oxygen fault in the oxide shell and interfaces between the crystalline Si core and the oxide shell, respectively.

Influence of hydrogen dilution on a-SiSn:H film growth and solar cell properties

In this contribution we report about improvement of the hydrogenated amorphous silicon tin (a-SiSn:H) thin film solar cells by using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) at the high hydrogen (H2) dilution conditions. Our studies revealed that the incorporation of Sn into a-SiSn:H does not depend much on the H2 dilution whereas it strongly depends on the Sn(CH3)4 and SiH4 mixture flow rate and the VHF input power density. On the other hand, the photoconductivity and solar cell performance were strongly improved with H2 dilution due to the better passivation of the Si- and Sn-related dangling bonds as was confirmed by their drastically reduced, broad and featureless ESR signals. Moreover, we believe that the reduction of carbon might be one of the reasons for the improvement of the a-SiSn:H solar cells. Our measurements of the external quantum efficiency (EQE) spectra and the I–V characteristics suggest that the H2 dilution plays an important role in the reduction of the photo-carrier killer sites, which opens a way for the fabrication of high quality a-SiSn:H thin films with enhanced photovoltaic performance.