Surface-wave Plasma Chemical Vapor Deposition Research Articles

Characterization of nitrogenated amorphous carbon thin films grown by microwave surface wave plasma CVD

We have studied the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of nitrogenated amorphous carbon thin films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were characterized by UV/VIS/NIR spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The lowest optical band gap (2.3 eV) was found at 90 Pa compared to the films deposited at other GCPs. The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm 2) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 90 Pa are 6.8 μA/cm 2, 147 mV, 0.186 and 1.8×10 −4%, respectively.

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C 10H 16O) dissolved with ethyl alcohol (C 2H 5OH), methane (CH 4), ethylene (C 2H 4) and acetylene (C 2H 2). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10 − 4 Ω − 1 cm − 1 ) and under the light illumination (i.e. 9.9 × 10 − 4 Ω − 1 cm − 1 ). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10 − 3 mA/cm 2. The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10 − 4 % and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.

Characterization of amorphous carbon films deposited by surface wave plasma CVD

Many dangling bonds in hydrogenated amorphous carbon ( a-C:H) films are usually generated by bombardments of high-energy ion precursors in typical chemical vapor deposition (CVD). To generate low dangling bonds, a-C:H films should be deposited from low-energy radical species. Surface wave plasma (SWP) generates low-energy and high-density radicals. We prepare a-C:H films using SWP and investigate the relationship between the plasma characteristics and structures of a-C:H films. The microwave of the TM01 mode was introduced through the dielectric window and SWP generate under the dielectric window. An Ar and C 2H 2 plasma mixture mainly consists of neutral radical species, and the electron temperature is as low as 1 eV. Electron density significantly decreases with increasing distance from the dielectric window. The a-C:H films are prepared from these hydrocarbon and carbon low-energy radicals as main precursors. The sp 2 bonded network cluster size in a-C:H films increase with electron density in SWP. This structure change is the influence of the termination structure of clusters changing to CH from CH 3 and CH 2.

Optical and structural properties of amorphous carbon thin films deposited by microwave surface-wave plasma CVD

Nitrogen doped amorphous carbon (a-C : N) thin films were deposited on silicon and quartz substrates by microwave surface-wave plasma chemical vapor deposition technique at low temperature (< 100 °C). We used argon (Ar), camphor dissolved in alcohol and nitrogen (N) as carrier, source and dopant gases, respectively. Optical band gap ( E g) decreased from 4.1 to 2.4 eV when the N gas concentration increased from 0 to 4.5%. The films were annealed at different temperatures ranging from 150 to 450 °C in Ar gas environment to investigate the optical and electrical properties of the films before and after annealing. Both E g and electrical resistivity ( ρ) decreased dramatically to 0.95 eV and 5.7 × 10 4 (Ω-cm) at 450 °C annealing. The structural modifications of the films leading to more graphite as a function of the annealing temperature was confirmed by the characterization of Raman spectra.

Photovoltaic characteristics of nitrogen-doped amorphous carbon thin-films grown on quartz and flexible plastic substrates by microwave surface wave plasma CVD

We report the photovoltaic characteristics of n-type conductivity of nitrogen-doped amorphous carbon (a-C:N) thin-films grown on quartz and heat tolerant (up to 260 °C) flexible polytetrafluoroethene plastic substrates by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) at low temperature (<100 °C). For film deposition at various gas composition pressures ranging from 50 to 90 Pa in the CVD chamber, we used argon as carrier gas, nitrogen as dopant and methane as carbon plasma source. The X-rays photoelectron spectroscopy (XPS) measurement shows that nitrogen content in the films grown on plastic substrates is higher compared with the films grown on quartz substrates. The optical measurements show that the optical band gap of the films grown on plastic substrate is lower compared with the films grown on quartz at the same parameters. The temperature dependence conductivity and photoresponse measurements show that the electrical conductivity of the films grown on plastic substrates is much higher compared with the films grown on quartz substrates. Our experimental results show that amorphous carbon deposited on flexible plastic substrates is reliable for photovoltaic applications.

THE INFLUENCE OF METHANE GAS PRESSURE ON THE OPTICAL, ELECTRICAL AND STRUCTURAL PROPERTIES OF NITROGENATED AMORPHOUS CARBON FILMS GROWN BY SURFACE WAVE MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

The influence of methane gas ( CH 4) pressure on the optical, electrical and structural properties of the nitrogenated amorphous carbon nitride ( a - C : N ) films grown by microwave surface wave plasma chemical vapor deposition (SWP-CVD) on quartz and silicon (100) substrates have been studied. The a - C : N films are deposited with varying CH 4 gas ranging from 5 to 20 ml/min. To incorporate nitrogen in the film, we have introduced nitrogen gas ( N ) at 5 ml/min in the chamber. The effects of CH 4 gas pressure on the surface morphology, composition, structure, and electrical properties of the N -incorporated camphoric carbon thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), UV-visible spectroscopy and four-probe resistance measurement. We have succeed in growing a - C : N thin films using SWP-CVD at room temperature and found that the amorphous structure of a - C films can be changed and is strongly dependent on the CH 4 gas source.

Incorporation of Nitrogen into Amorphous Carbon Films Produced by Surface-Wave Plasma Chemical Vapor Deposition

In order to study the influence of nitrogen incorporated into amorphous carbon films, nitrogenated amorphous carbon films have been deposited by using surface wave plasma chemical vapor deposition under various ratios of N2/CH4 gas flow. Optical emission spectroscopy has been used to monitor plasma features near the deposition zone. After deposition, the samples are checked by Raman spectroscopy and x-ray photo spectroscopy (XPS). Optical emission intensities of CH and N atom in the plasma are found to be enhanced with the increase in the N2/CH4 gas flow ratio, and then reach their maximums when the N2/CH4 gas flow ratio is 5%. A contrary variation is found in Raman spectra of deposited films. The intensity ratio of the D band to the G band (ID/IG) and the peak positions of the G and D bands all reach minimums when the N2/CH4 gas flow ratio is 5%. These show that the structure of amorphous carbon films has been significantly modified by introduction of nitrogen.