Ashraf M.M. Omer

Photovoltaic characteristics of postdeposition iodine-doped amorphous carbon films by microwave surface wave plasma chemical vapor deposition

The amorphous carbon thin films have been deposited on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature (<100°C) in Ar∕CH4 phase gas. Doping of iodine has been done in the postdeposited films by exposing them in iodine vapor. The photovoltaic measurements of the films were carried out before and after iodine doping. The results show dramatic decrease of optical gap from 3.4 to 0.9 eV corresponding to nondoping to iodine doping conditions, respectively. The preliminary photovoltaic characteristics of the film deposited on n-type silicon substrate under light illumination (AM1.5, 100mW∕cm2) reveal a short-circuit current density of 1.15μA∕cm2, open-circuit voltage of 177 mV and fill factor of 21.7%.

THE OPTICAL PROPERTIES OF NITROGENATED AMORPHOUS CARBON FILMS GROWN BY A NOVEL SURFACE WAVE MICROWAVE PLASMA CVD METHOD

The effects of annealing temperature on the optical properties of nitrogenated amorphous carbon (a-C:N) films grown on quartz substrates by a novel surface wave microwave plasma chemical vapor deposition (SWMP-CVD) method are reported. The thickness, optical, structural and bonding properties of the as-grown and anneal-treated a-C:N films were measured and compared. The film thickness decreased rapidly with increasing annealing temperature above 350°C. A wide range of optical absorption characteristics is observed, depending on the annealing temperature. The optical band gap of as-grown a-C:N films is approximately 2.8 eV, gradually decreasing to 2.5 eV for the films anneal-treated at 300°C, and beyond that decreasing rapidly down to 0.9 eV at 500°C. The Raman and FTIR spectroscopy measurements have shown that the structural and composition of the films can be tuned by optimizing the annealing temperature. The change of optical, structural and bonding properties of SWMP-CVD-grown a-C:N films with higher annealing temperature was attributed to the fundamental changes in the bonding and band structures of the films.

Structural, Optical and Electrical Characterization of Amorphous Carbon Thin Films Grown on PTFE Substrates for Photovoltaic Application

The n-type conductivity of nitrogen doped amorphous carbon films have been grown on p-type silicon, quartz and heat tolerant (up to 260 degC) flexible polytetrafluoroethene plastic substrates by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) at low temperature (<100 degC). For film deposition at gas composition pressure of 50 Pa in the CVD chamber, we used argon as carrier gas, nitrogen as dopant and methane as carbon plasma source. Photovoltaic effects of the films as well as their chemical composition, bonding and structural properties have been studied. The X-rays photoelectron spectroscopy 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

EFFECTS OF METHANE GAS FLOW RATE ON THE OPTOELECTRICAL PROPERTIES OF NITROGENATED CARBON THIN FILMS GROWN BY SURFACE WAVE MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

We have studied the influence of the methane gas (CH4) flow rate on the composition and structural and electrical properties of nitrogenated amorphous carbon (a-C:N) films grown by surface wave microwave plasma chemical vapor deposition (SWMP-CVD) using Auger electron spectroscopy, X-ray photoelectron spectroscopy, UV-visible spectroscopy, four-point probe and two-probe method resistance measurement. The photoelectrical properties of a-C:N films were also studied. We have succeeded to grow a-C:N films using a novel method of SWMP-CVD at room temperature and found that the deposition rate, bonding and optical and electrical properties of a-C:N films are strongly dependent on the CH4 gas sources, and the a-C:N films grown at higher CH4 gas flow rate have relatively high electrical conductivity for both cases of in dark and under illumination condition.

Amorphous carbon thin film deposition by microwave surface-wave plasma CVD for photovoltaic solar cell

Amorphous carbon (a-C) thin films were successfully deposited on various substrates, such as, silicon, quartz, glass and flexible plastic at low temperature (<100/spl deg/C) by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD), a newly developed deposition method for solar cell application. The camphor dissolved with alcohol mixture and methane were used as carbon precursors, while argon was used as carrier gas. Nitrogen and iodine were used as dopants. The deposited a-C films were characterized by UV/VIS/NIR spectrophotometer, SEM, Raman scattering and XPS measurements. In this paper, we report experimental results of the optical, physical and structural properties of the films; the results suggested that it is possible to control film growth rate and optical band gap, and consequently improve photoconductivity by proper selection of deposition parameters, optimizing dopants and appropriate annealing temperature. Our research work is in a progressive stage to realize cheap, reasonably highly efficient and environmentally friendly a-C-based photovoltaic solar cell in the future.

Photovoltaic Properties of a-C:N/p-Si Heterojunction Solar Cell Synthesized by Microwave Surface Wave Plasma CVD

Amorphous carbon (a-C) thin films have been synthesized by microwave surface wave plasma chemical vapor deposition at low temperature (<100 degC). The influence of nitrogen doping on the properties a-C films is reported. Argon, acetylene and nitrogen (N) were used as a carrier, source and dopant gases. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Solar simulator were employed to investigate chemical, optical, structural and electrical properties of the films. Successfully nitrogen incorporated (29.37 at. %) into the film was found. The optical band gaps decreased from 2.7 to 1.7 eV. The photovoltaic measurements of a-C:N/p-Si structure show that the open-circuit voltage (Voc) of 4.7 mV and a short-circuit current density (Jsc) of 19.6 muA/cm2 under light illumination (AM 1.5 100 mW/cm2). The energy conversion efficiency and fill factor of the solar cell were found to be 2.24times10-4 % and 0.24 respectively

PHOTOCONDUCTIVITY EFFECTS OF NITROGENATED CARBONACEOUS FILMS GROWN ON VARIOUS TYPES OF SUBSTRATES BY SURFACE WAVE MICROWAVE PLASMA CVD

The n-type conductivity nitrogen-doped amorphous carbon (n-C) films have been grown by surface wave microwave chemical vapor deposition (SWP-CVD) on plastic and quartz substrates. The bonding, electrical and photovoltaic properties have been studied. The Tauc plot of UV-Visible measurement have shown that n-C films deposited on plastic have smaller optical band gaps compared to the films grown on quartz substrate at the same parameters. Temperature dependence and photoresponse measurements also have shown that the properties of n-C thin films deposited on plastic have higher photoelectrical response. Our experimental results have shown that the flexible polytetrafluoroethene plastic substrate is a reliable candidate for future photovoltaic applications.

Photovoltaic Characteristics of Nitrogen Doped Amorphous Carbon Film Grown by Microwave Surface Wave Plasma CVD

Photovoltaic properties of nitrogen doped amorphous carbon (a-C:N) thin films deposited on p-type silicon (p-Si) and quartz substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at low temperature (<100 degC) are analyzed in this section. Argon (Ar: 200 sccm), methane (CH4:10 sccm) and nitrogen (N: 5 sccm) were used as carrier, source and doping gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy and solar simulator were employed to investigate the chemical, optical and photovoltaic properties of the a-C:N film respectively. The optical gap of the film was found to be 2.3 eV. The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm 2) shows that short circuit current density, open circuit voltage, fill factor and photo-conversion efficiency of the film are 0.003 mA/cm, 0.108 V, 0.25 and 1.8times10-4 respectively which suggests the formation of heterojunction between the a-C:N and p-Si

The Characteristic Of As-Grown And Post-Annealed Nitrogen Doped Amorphous Carbon Thin Films Deposited By Surface Wave Microwave Plasma Enhanced Chemical Vapor Deposition Method

Nitrogen doped amorphous carbon (a-C:N) thin films were deposited on silicon and quartz substrates by microwave surface-wave plasma chemical vapor deposition (SWMP-CVD) technique at low temperatures (<100°C). We used argon (Ar), camphor dissolved in alcohol, and nitrogen (N) as carrier, source, and dopant gases, respectively. Optical band gap (Eg) 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°C to 450°C in Ar gas environment to investigate the optical and electrical properties of the films before and after annealing. Both Eg and electrical resistivity (ρ) decreased dramatically up to 0.95 eV and 57×103 Ω cm at 450°C annealing. The structural modifications of the films leading them to become more graphitized as a function of the annealing temperature were confirmed by the characterization of Raman spectra.

The Raman spectra characteristics of a-CNx films grown on quartz substrates by newly developed surface wave microwave PECVD

Amorphous carbon nitride (a-CNx) films were deposited on quartz substrates by newly developed surface wave microwave plasma chemical vapor deposition (SWMP-CVD) of alcohol camphoric carbon plasma source at room temperature. Then the a-CNx films were heat-treated at various annealing temperatures (AT) in the 100–500°C range. The effects of heat treatment on the structural modifications were studied by Visible-Raman spectroscopy through the evolution of D and G peaks. The spectral evolution observed on heat-treated a-CNx shows progressive formation of crystallites. Raman spectra have revealed the amorphous structure of as-grown a-CNx films and the growth of nanocrystallinity upon increase of AT. These structural changes were further correlated with optical band gap and fraction of sp3 bonded carbons present, derived respectively from the UV-visible and photoelectron spectroscopy. The wide range of optical absorption coefficient characteristics is observed depending on the AT. The optical band gap of as-grown a-CNx films is found to be approximately 2.8 eV; it gradually decreases to 2.5 eV for the films heat-treated at 300°C and then it decreases rapidly to 0.9 eV at 500°C. The results obtained are discussed and compared with the literatures.