Effect Of Hydrogen Plasma Treatment Research Articles

Effects of hydrogen plasma treatment on the electrical behavior of solution-processed ZnO transistors

The effects of hydrogen plasma treatment on the active layer of top-contact zinc oxide thin film transistors are reported. The transfer characteristics of the reference devices exhibited large hysteresis effects and an increasing positive threshold voltage (VTH) shift on repeated measurements. In contrast, following the plasma processing, the corresponding characteristics of the transistors exhibited negligible hysteresis and a very small VTH shift; the devices also possessed higher field effect carrier mobility values. These results were attributed to the presence of functional groups in the vicinity of the semiconductor/gate insulator interface, which prevents the formation of an effective channel.

Hydrogen passivation of self-assembled Ge/Si quantum dots

We studied the effect of hydrogen plasma treatment on room-temperature photoluminescence of self-assembled Ge/Si quantum dots by varying temperature and duration of treatment. Hydrogen plasma exposure at for 30 min was found to result in the improvement in the radiative efficiency of the Ge quantum dots by one order of magnitude. The enhancement of the photoluminescence intensity is thought to be due to the passivation of nonradiative centers located nearby or inside the dots via formation of Si–H bonds. Infrared absorption spectroscopy was used to correlate photoluminescence results.

Direct observation and mechanism for enhanced electron emission in hydrogen plasma-treated diamond nanowire films.

The effect of hydrogen plasma treatment on the electrical conductivity and electron field emission (EFE) properties for diamond nanowire (DNW) films were systematically investigated. The DNW films were deposited on silicon substrate by N2-based microwave plasma-enhanced chemical vapor deposition process. Transmission electron microscopy depicted that DNW films mainly consist of wirelike diamond nanocrystals encased in a nanographitic sheath, which formed conduction channels for efficient electron transport and hence lead to excellent electrical conductivity and EFE properties for these films. Hydrogen plasma treatment initially enhanced the electrical conductivity and EFE properties of DNW films and then degraded with an increase in treatment time. Scanning tunneling spectroscopy in current imaging tunneling spectroscopy mode clearly shows significant increase in local emission sites in 10 min hydrogen plasma treated diamond nanowire (DNW10) films as compared to the pristine films that is ascribed to the formation of graphitic phase around the DNWs due to the hydrogen plasma treatment process. The degradation in EFE properties of extended (15 min) hydrogen plasma-treated DNW films was explained by the removal of nanographitic phase surrounding the DNWs. The EFE process of DNW10 films can be turned on at a low field of 4.2 V/μm and achieved a high EFE current density of 5.1 mA/cm(2) at an applied field of 8.5 V/μm. Moreover, DNW10 films with high electrical conductivity of 216 (Ω cm)(-1) overwhelm that of other kinds of UNCD films and will create a remarkable impact to diamond-based electronics.

Plasma-chemical reduction of iron oxide photoanodes for efficient solar hydrogen production

We demonstrate the effect of hydrogen plasma treatment on hematite films as a simple and effective strategy for modifying the existing substrate to improve significantly the band edge positions and photoelectrochemical (PEC) performance. Plasma treated hematite films were consist of mixed phases (Fe3O4:α-Fe2O3) which was confirmed by XPS and Raman analysis, treated films also showed higher absorption cross-section and were found to be a promising photoelectrode material. The treated samples showed enhance photocurrent densities with maximum of 3.5 mA/cm2 at 1.8 V/RHE and the photocurrent onset potentials were shifted from 1.68 VRHE (untreated) to 1.28 VRHE (treated). Hydrogen plasma treatment under non-equilibrium conditions induced a valence dynamics among Fe centers in the sub-surface region that was sustained by the incorporation of hydrogen in the hematite lattice as supported by the density functional theory calculations.

Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching.

Reduced defect density in microcrystalline silicon by hydrogen plasma treatment

The effect of hydrogen plasma treatment (HPT) during the initial stage of microcrystalline silicon (μc-Si) growth on the defect density of μc-Si has been investigated. Lower absorption coefficient in the 0.8–1.0 eV indicated less defect density compared to its counterpart without HPT. The infrared spectroscopy of μc-Si with HPT shows an increase in 2040 cm−1, which reveals more Si—H in the amorphous/crystalline interfaces. We ascribe the decrease of defect density to hydrogen passivation of the dangling bonds. Improved performance of μc-Si solar cell with HPT is due to the reduced defect density.

Enhanced field-emission capacity by density control of a CNT cathode using post-plasma treatment

The effects of hydrogen plasma treatment on surface morphologies and field emission performance of vertically aligned multi-walled carbon nanotubes were investigated. The hydrogen plasma treatment of vertically aligned multi-walled carbon nanotubes induces changing surface morphologies from flat surface to sharp conical shapes according to the plasma treatment time. The morphological changes owing to plasma treatment enhances field emission performance of vertically aligned carbon nanotubes so that the current density and field enhancement factor were considerably improved compared to those of as-grown one.

Effects of hydrogen plasma treatment on SnO2:F substrates for amorphous Si thin film solar cells

We investigated the effects of hydrogen plasma treatment on the physical and electrical properties of fluorine-doped tin oxide (FTO) films used for amorphous silicon (a-Si) thin film solar cells. A slight increase in carrier concentration by the hydrogen doping effect was observed for the FTO film exposed to the hydrogen plasma for 5 min. For further exposure to the plasma, the chemical reduction became prominent and resulted in deterioration of the electrical and optical properties of the film. XPS analysis revealed that the chemical reduction of SnO2 to Sn metallic state occurs on the surface region. It was found that the defects formed by hydrogen plasma act as recombination centers at the interface between FTO electrode and p-layer of a-Si solar cells. This phenomenon resulted in the deterioration of the cell performance. The averaged conversion efficiency (6.82%) of the cells on pristine FTO hydrogen substrate was decreased to 5.81% for the cells on FTO treated for 5 min, which is mainly attributed to the decrease in short-circuit current density.

Effect of hydrogen plasma treatment on nano-structured TiO2 films for the enhanced performance of dye-sensitized solar cell

We report an efficient method to improve the efficiency and stability of DSSC with nano-structured TiO2. A low temperature RF plasma-enhanced chemical vapor deposition (PECVD) system was utilized for hydrogen plasma treatment on nano-structured TiO2 film. We confirmed that the efficiency of DSSCs was significantly dependent on the plasma power. This increased the hydrophilic property, the excess electrons and dye adsorption on its surface. The relative change in surface chemistry and hydrophilic characteristics with plasma treatment was investigated using various analysis methods. In our study, we showed that DSSC with plasma-treated TiO2 had a power conversion efficiency of 6.94%, which is 21% higher than that without plasma treatment. It was found that the plasma treatment caused both increased dye adsorption and significant longer electron lifetime.

Effects of hydrogen plasma treatment on microstructure evolution and electrical conductivity of electroless Ni–P coatings on polyimide and glass substrates

Electroless Ni–P coatings with various thicknesses were deposited on polyimide and glass substrates, and subsequently subjected to heat treatment in air as well as microwave-assisted hydrogen plasma treatment. The effects of substrate and hydrogen plasma treatment on the microstructure and electrical conductivity were examined in detail using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and the Hall Effect measurement. The results indicated that the substrate materials may influence the deposition rate, the grain size, the type of metastable phase, crystallinity, resistivity, carrier mobility, and carrier concentration of Ni–P coatings. Furthermore, the 600W hydrogen plasma treatment for 1min can yield coatings with a more uniform and lower resistivity, compared with coatings at the as-deposited state or after heating at 300°C for 3h in air. The Ni–P coatings after plasma treatment exhibited higher carrier mobility, whereas coatings at the deposited state exhibited higher carrier concentration. In addition, prior to plasma treatment, a heat treatment in air enhances the conductivity of Ni–P coatings.

The effect of hydrogen plasma treatment on the Au–CdZnTe interface

This paper investigates the hydrogen plasma treatment effects on the interface of Au/CdZnTe contact. Hydrogen plasma with high energy is the smallest and lightest atomic mass, which is easy to enter into the crystal surface to fill the vacancy defects. The Au/CdZnTe samples were treated by the microwave hydrogen plasma with the power of 60W (average power density of 0.5W/cm2) and the frequency of 13.6MHz under different treatment times. Scanning electron microscope (SEM), current–voltage (I–V) and adhesion strength measurement were performed to analyze the interface properties of Au/CdZnTe before and after the hydrogen plasma treatment. The results show that the hydrogen plasma treatment can reduce the surface leakage current, decrease the point defects and improve the performance of the electrode contacts.

N-type silicon RST ribbon solar cells

In this work, we report for the first time on the electronic properties and the solar cell fabrication on N-type silicon ribbons grown by the RST method. We have investigated the majority charge carriers' parameters (resistivity and mobility) and the minority carrier lifetime (MCL) of N-type silicon RST ribbons. The MCL values are deduced using the photoconductivity decay method on RST wafers, the surface of which was passivated by an iodine/ethanol solution. The effect of hydrogen plasma treatment on the electronic properties of the as-grown RST ribbons was also studied. We show that the bulk passivation following hydrogen plasma treatment, carried out at temperatures above 350°C for more than 1h, strongly improves the MCL. Conventional solar cells were prepared on RST ribbons grown in optimized conditions and passivated by plasma hydrogenation. Two types of boron emitters were tested, namely those obtained by boron-spin-coating and by ion implantation, while the N+ region serving as a back surface field was made by phosphorus spin coating. The highest conversion efficiency values obtained for boron-implantation (B-II) and boron-spin-coating (B-SOD) emitters on a ∼120μm thick RST were 13.8% and 12.7% respectively, with no surface texturing, or optimized surface passivation. Suns-Voc method applied to these RST cells gave, for B-II and B-SOD emitters conversion efficiencies of about 15.1% and 13.6%, respectively. The former value represents to our knowledge the highest efficiency value obtained for ultrathin N-type multi-crystalline silicon ribbon based cells.

Improvement the Open Circuit Voltage of Amorphous Silicon Solar Cells by Treating the P Layer with Hydrogen Plasma

It is necessary to improve the open circuit voltage of amorphous silicon solar cells for its applications. In this paper, we discuss the effects of hydrogen plasma treatment on the P layer and the performance of the amorphous silicon solar cells. The result shows that the open circuit voltage increased by 0.0257V, the fill factor increased by 0.039 and the energy conversion efficiency increased by 9%. The highest VOCwe got was 0.99V. Treating P layer with hydrogen plasma has been demonstrated to result in materials with improved crystalline volume fraction which was very effective to increase the light absorption of the intrinsic layer. What is more, it could be easily integrated into the amorphous silicon solar cell mass production process.

Effects of hydrogen plasma treatment on the structural and electrical properties of sputter-deposited SnO2 thin films

In this paper, we report the effects of hydrogen plasma treatment on the structural and electrical properties of SnO2 thin films prepared by the sputtering method. Whereas the hydrogen plasma treatment led to etching of SnO2 films and subsequent degradation of crystalline quality and optical transmittance, the plasma-treated films exhibited an improvement in the electrical conductivity. Hall measurements indicated an increase in the carrier concentration of SnO2 films which, following x-ray diffraction and secondary ion mass spectrometry measurements, was attributed to the generation of oxygen vacancies rather than the incorporation of hydrogen shallow donors in undoped SnO2 films.

Effect of hydrogen plasma treatment on reduction process of iron oxide nanoparticles

Fe3O4 nanoparticles coated with oleic acid as a surfactant were reduced by hydrogen plasma generated by 13.56 MHz Radio-Frequency (RF). With increasing input RF power to the inductive coil, Fe3O4 nanoparticles could be transformed to almost single phase of Fe3C and finally to α-Fe. The average grain sizes of Fe3C and α-Fe nanoparticles are 19 – 23 nm and 52 -59 nm, respectively. Saturation magnetizations of Fe3C and α-Fe nanoparticles at 5 K were almost same as these of bulk Fe3C and α-Fe. Field cooling procedure from room temperature to 5 K in the magnetic measurement revealed a formation of FeO phase from Fe3O4 by weak reduction. The desired ranges of electron temperature and electron density in order to obtain Fe3C and α-Fe phases were determined by investigating plasma characteristics.

Electrical Properties of Hydrogen Terminated P-Type Diamond Film

Undoped high quality polycrystalline diamond films were grown by the microwave plasma chemical vapor deposition (MPCVD) method. The effects of hydrogen plasma treatment and vacuum annealing process on the p-type behavior of diamond films were investigated by the Hall effect method. The sheet carrier concentration increased and the sheet resistivity decreased with the treating time of hydrogen plasma and a stable value was achieved finally. After annealing the samples in vacuum at temperature above 600 °C, the sheet carrier concentration dropped dramatically. The origin of this hydrogen terminated p-type conductive layers is also discussed.

Effect of hydrogen plasma treatment on the field emission of diamond-like films deposited by high power excimer laser ablation

The effect of hydrogen plasma treatment on the electron field emission of diamondlike carbon films (DLCs) deposited by high frequency and high power pulsed XeCl excimer laser ablation of pyrolytic graphite targets at room temperature was studied. Results indicated that the films exhibited improved electron emission, with the threshold field of the films decreased from 26 to 19 V/μm. Meanwhile, the current density increased considerably after the treatment. Two factors were responsible for the results. One was that the graphiterich DLC film surface formed with low energy carbon atoms or clusters during growth process was removed by the hydrogen plasma with the formation of a new surface comprised of high density sp3 bonded carbons, which exhibited a low electron affinity and good field emission . The other was that the dangling bonds of the carbon atoms on the film surface were saturated with Hatoms after the treatment, which further decreased the electron affinity.

Effect of hydrogen plasma treatment on the surface morphology, microstructure and electronic transport properties of nc-Si:H

Hydrogenated nanocrystalline silicon (nc-Si:H) films, deposited by reactive radio-frequency sputtering with 33% hydrogen dilution in argon at 200 °C, were treated with low-power hydrogen plasma at room temperature at various power densities (0.1–0.5 W/cm 2) and durations (10 s–10 min). Plasma treatment reduced the surface root mean square roughness and increased the average grain size. This was attributed to the mass transport of Si atoms on the surface by surface and grain boundary diffusion. Plasma treatment under low power density (0.1 W/cm 2) for short duration (10 s) caused a significant enhancement of crystalline volume fraction and electrical conductivity, compared to as-deposited film. While higher power (0.5 W/cm 2) hydrogen plasma treatment for longer durations (up to 10 min) caused moderate improvement in crystalline fraction and electrical properties; however, the magnitude of improvement is not significant compared to low-power (0.1 W/cm 2)/short-duration (10 s) plasma exposure. The results indicate that low-power hydrogen plasma treatment at room temperature can be an effective tool to improve the structural and electrical properties of nc-Si:H.

Effects of Hydrogen Plasma Treatment on the Electrical and Optical Properties of ZnO Films: Identification of Hydrogen Donors in ZnO

Wurtzite ZnO has many potential applications in optoelectronic devices, and the hydrogenated ZnO exhibits excellent photoelectronic properties compared to undoped ZnO; however, the structure of H-related defects is still unclear. In this article, the effects of hydrogen-plasma treatment and subsequent annealing on the electrical and optical properties of ZnO films were investigated by a combination of Hall measurement, Raman scattering, and photoluminescence. It is found that two types of hydrogen-related defects, namely, the interstitial hydrogen located at the bond-centered (H(BC)) and the hydrogen trapped at a O vacancy (H(O)), are responsible for the n-type background conductivity of ZnO films. Besides introducing two hydrogen-related donor states, the incorporated hydrogen passivates defects at grain boundaries. With increasing annealing temperatures, the unstable H(BC) atoms gradually diffuse out of the ZnO films and part of them are converted into H(O), which gives rise to two anomalous Raman peaks at 275 and 510 cm(-1). These results help to clarify the relationship between the hydrogen-related defects in ZnO described in various studies and the free carriers that are produced by the introduction of hydrogen.

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes