CdS thin films grown on ITO/glass substrates by using chemical bath (CB) were boron-implanted employing 100keV beam of boron ions (B+) with fluences in the range 1.0×1015–1.0×1016ions/cm2. The B doping was successfully carried out, as was proved by the major carrier density introduced in the range 0.8×1018–5.4×1018cm−3, which was calculated from thermo power measurements. Raman spectroscopy results support the assumption that triply ionized boron (B3+) enters into the CdS lattice occupying Cd2+ sites, which create shallow donor levels in the forbidden energy band gap.

The research and development of microcrystalline 3C-SiC, SiGeC and GeC thin films for solar cell applications are presented. Hot Wire CVD technique is employed to optimize the deposition parameters for achieving high quality mu c-3C-SiC thin films whose bandgap is 2.2eV. Monomethylsilane and hydrogen are used as reactant gases for the deposition of mu c-SiC thin films. P and All are used as dopants to successfully obtain n and p type mu c-3C-SiC thin films. Doped mu c-3C-SiC is very attractive for the potential window layer applications in Si thin film and Si heterojunction solar cells. Attempts to control the bandgap of mu c-3C-SiC are done by incorporating Ge into SiC. Of late, we have succeeded to prepare mu c-3C-SiGeC with a Ge content of 5%, which showed about 0.2eV lower absorption spectra compared to that of 3C-SiC.

Heterojunction diodes are fabricated by fluorine ion implanted amorphous, carbon (a-C: H) on p-type Si substrates. Various metallic contacts are formed on the fluorine implanted carbon side and copper contact is found to result in better a-C/p-Si heterojunction, and is found to be dose dependent. Formation of heterojunction diode confirms that the fluorine ion implanted a-C is n-type. Electrical resistivity is found to reduce with the ion dose and is attributed to the fluorine ions and ion beam induced localized heating effects. Raman scattering studies resulted in the formation of typical disorder D and graphitic G Raman bands in the implanted carbon films.

Microcrystalline and nanocrystalline diamond thin films deposited on Si substrates by microwave plasma chemical vapor deposition are bombarded by 40 keV B+ ions. Raman scattering studies of the ion implanted diamond films reveal the structural modification irrespective of the nature of the crystalline quality. X-ray diffraction results indicate the possibility of formation of borocarbide phase on ion irradiation. Ion beam current dependence and post ion implantation annealing studies on the micro and nano-crystalline thin films are also presented.

An attempt to improve the efficiency of the heterojunction p-a:C/n-Si has been made by introducing the highly insulating C60 layer between the semiconductor layers of the cell structure. The conductivity of the implanted films is found to increase during the implantation process and it is attributed to the complete disintegration of the fullerene molecules. The efficiency of this structure is found to be 0.1% under AM 1.5 conditions which is ten times higher than the cell fabricated using the boron ion implanted fullerene without the insulating layer.

Boron ions of 65 keV are bombarded into hydrogenated a-carbon films deposited by radio frequency plasma chemical vapor deposition technique. Ion beam current dependence studies on the physical properties of a-C films for a fixed boron dose of 1×1016 ions/cm2 reveal the reduction in resistivity, whereas the optical gap is found to be unaffected. The structural phase transition accompanied by the reduction in the optical gap and resistivity takes place when the ion dose is increased. These changes are due to the production of defect levels and localized heating effects during the ion implantation process.

The fullerene thin films (bucky balls) on irradiation are found to undergo cracking (disintegration) resulting in the formation of the conducting amorphous carbon. Reduction in the resistivity and optical gap were observed during the irradiation process. The films on boron and phosphorous ion implantation resulted in the p and n type semiconducting amorphous carbon. Solar cells fabricated from the excimer laser irradiated films of C/sub 60/ sandwiched with n-type Si resulted in the efficiency of 0.7%.

Thin films of fullerene C60 deposited by the molecular-beam epitaxy method have been subjected to a 248 nm excimer laser for various timings. Reduction in the electrical resistance of the films and the spectral evolution of the D and G bands in the Raman spectra, due to the sharp tendency towards graphitization accompanied by an increasing level of structural disorder, are observed during laser irradiation. Based on the above results, an attempt has been carried out on these irradiated C60 films to make a device sandwiched with n-type Si, and the photovoltaic parameters are reported as a function of the laser exposure times.

Thin films of C60 deposited on p-type Si(100) wafer are implanted with low energy phosphorous ions for the photovoltaic applications. An attempt has been made on the device fabrication with phosphorous ion implanted C60 films grown on the p-type Si wafer. The photovoltaic properties of the solar cell structure are discussed with the dark and illuminated J–V characteristics. The efficiency of the structure in the multiple energy phosphorous ion implanted C60 film/p-Si heterojunction is found to be 0.01% under air mass 1.5 conditions. The low efficiency is attributed to the ion implantation induced damage effects and subsequent larger series resistance values.

C60 films have been bombarded with low energy boron ions and high energy swift heavy ions (SHI) of silver and oxygen at different doses. Raman scattering and Fourier transform infrared (FTIR) studies were carried out on the virgin and irradiated films and the results are in good agreement with each other. The films subject to low energy boron ion implantation showed destruction of the bukky balls whereas the films subject to high energy ion irradiation did not show appreciable effects on their structure. These results indicate that C60 films are more prone to defects by elastic collision and subsequent implantation at lower energy. Irradiation at higher energy was less effective in creating appreciable defects through electronic excitation by inelastic collisions at similar energy density.

Conductivity control of the boron and phosphorus ion implanted C-60 films subjected to various doses with multiple energy has been investigated. Temperature dependent conductivity shows the semiconducting nature of the B+ and P+ implanted films. Fourier transform infrared spectra of the B+ and P+ implanted C-60 films show the structural change of the C-60 into amorphous carbon. Optical gaps of the implanted films have been observed as a function of implantation dose. The dramatic increase in the conductivity and the reduction in the optical gap on ion implantation are thought to be attributed to an increase in sp(2) bounded states, lattice damage, and substitutional impurity doping with ion implantation. The B+ and P+ implantation into C-60 and amorphous carbon suggests the possibility of fabricating carbon based homojunction solar cells. (C) 2001 American Institute of Physics.

Persistent photoconductivity (PPC) in nitrogen ion irradiated CdS thin films prepared by chemical bath deposition (CBD) technique is reported. The PPC phenomenon observed in the nitrogen ion irradiated CdS thin films is due to the complex nature of the defects caused during irradiation. Nitrogen ion implantation caused the reduction in the optical band gap of the films revealing the formation of defect levels. The structure of the virgin and implanted films studied using the X-ray diffraction technique is reported.

An attempt has been made on the device fabrication with boron ion implanted C60 thin films. The C60 thin films evaporated on n-type Si (100) have been implanted with mass analyzed positive boron ions at a fixed energy of 80keV to different doses in the range 1×1012−1×1015ions/cm2. Raman scattering and FTIR studies of the high-dose implanted films reveal the formation of amorphous carbon layer. Hall effect measurements indicate the formation of p-type conductivity in C60 thin films with boron ion implantation. In order to realize uniform boron distribution in the C60 films, multiple boron implantation with energies in the range of 50–80keV has been examined and p-type C60/n-type Si heterojunction solar cells with an efficiency as high as 0.023% have been fabricated. The photovoltaic properties of the solar cell structure are discussed along with the dark and illuminated I—V characteristics.

We report here the high-energy (1 MeV) electron irradiation effects on C60 films. Fourier transform infrared spectroscopy, Raman spectroscopy, and x-ray diffraction results are consistent and provide clear evidence of the nondestruction of C60 molecules upon irradiation. The presence of C60 signature peaks in the spectra of all three techniques indicates that the C60 films have not been transformed into a hitherto proposed structure of amorphous carbon for low-energy irradiation. A very short collision time mechanism has been proposed to explain the observation.

CdS thin films prepared by vacuum evaporation method were implanted with oxygen ions at the energy of 80 keV to different doses. Raman scattering studies of the as-deposited and implanted films reveal the shift in the Raman peak position of A1(LO) mode towards higher wave number on implantation. The area under the peak increases with dose initially, and then decreases at higher doses. The shift of the Raman peak to higher wave numbers has been attributed to the replacement of sulphur atoms by the lighter oxygen atoms.

An attempt has been made on the device fabrication with boron ion-implanted C60 thin films grown on n-type Si (100) by molecular-beam epitaxy. The studies on the films implanted to a dose of 1×1014 ions/cm2 with multiple B ion energies in the range of 50–80 keV reveal p-type conduction in the B ion-implanted C60 thin films as a result of amorphous carbon layer formation by B ion implantation. In addition, p-type B-implanted C60/n-type Si heterojunction solar cells with a conversion efficiency as high as 0.02% higher than previous highest value ever reported have been fabricated. The photovoltaic properties of the solar-cell structure are discussed along with the dark and illuminated I–V characteristics.

Type conversion due to nitrogen ion irradiation in CdS thin films prepared by chemical bath deposition (CBD) is reported. The films were bombarded with various doses of nitrogen ions in the range 1014–1017 ions/cm2, at an energy of 130 keV. The electrical conductivity of the films was found to increase with increase in nitrogen ion concentration. The temperature dependence of conductivity showed an activation energy of 0.06 eV, indicating shallow level formation due to implantation. Hot-probe measurements revealed p-type conductivity in implanted samples and n-type conductivity in unirradiated samples. X-ray diffraction results revealed CdS to be the predominant phase even after nitrogen ion irradiation.