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Study on the Effects of H+ and He+ Implantation in Semi-Insulating GaAs by Using Raman Spectroscopy
santhakumar kannappan,Cheul-Ro LEE,Hayakawa Y,Jayavel P,Jin soo Kim,Kesavamoorthy R,Muraleedaran Nair,Tetsuo soga 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Fifty-keV hydrogen-ion (H$^+$) and 70-keV helium-ion (He$^+$) implantation with doses from 10$^{13}$ to 10$^{16}$ cm$^{-2}$ in semi-insulating (100) gallium-arsenide (GaAs) single- crystal substrates have been carried out. Raman spectra of as-grown, implanted, and post-implantation-annealed GaAs samples are analyzed. Two LO phonon modes have been observed for all the samples. The lower wavenumber peak is attributed to the strained surface layer whereas the higher wavenumber peak is due to bulk GaAs crystal. For H$^+$ implantation, the peak positions of both peaks shift towards lower wavenumber up to a dose of 10$^{14}$ cm$^{-2}$ due to passivation of charge carriers. For higher doses, the peak positions shift towards higher wavenumber due to hydrogen-filled vacancy loops. On the other hand, for He$^+$-implanted samples, the peak positions increase for doses up to 10$^{13}$ cm$^{-2}$ and then decrease at higher doses. The immiscible nature of helium at low doses causes the increase in the peak positions. In contrast, implantation-induced damage is dominant at higher doses. Implantation-induced defects are partially annealed by post-implantation annealing, causing a blueshift of the peak positions for the H$^+$-implanted samples. In He$^+$-implanted samples, the peak positions redshift due to annealing of He interstitials at low doses and blueshift due to annealing of implantation-induced defects at high doses.
Palanisamy Kumar,Santhakumar Kannappan,Shizuyasu Ochiai,신백균 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8
In the present work, we have demonstrated high-performance organic solar cells with spray coated active layers. The influence of the nanomorphology on the power conversion efficiency of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C71-butyric acid (PC71BM)methyl ester bulk heterojunction solar cells is presented. Active layers were prepared using a chlorobenzene solvent containing a small volume of 1,8-diiodooctane as an additive by spray coating with conventional handheld airbrushes. The surface morphology of the active layers deposited for various spray-coating times was examined using atomic force microscopy. The resulting devices were measured under AM 1.5G (100 mW/cm2) conditions in an ambient atmosphere. The optimized spray-coated PTB7:PC71BM film showed a high solar cell performance with a short-circuit current density of 14.20 ± 0.41 mA/cm2, a fill factor of 56.00 ± 0.02% and a power conversion efficiency of 5.96 ± 0.15%.
Shizuyasu Ochiai,Palanisamy Kumar,Kannappan Santhakumar,신백균 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.4
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conducting polymer, has been receiving a great deal of attention for next generation optoelectronic organic devices. In this report, we discuss the effect of additives along with the thickness of PEDOT:PSS layers on the power conversion efficiency of organic solar cell devices. PEDOT:PSS films treated with high boiling point solvents of dimethyl sulfoxide (DMSO) and ethylene glycol (EG) show a significant enhancement in electrical conductivity without compromising flexibility or optical transparency. The conductivity increased from 0.5 to 517 and 724 S/cm after once and thrice treatment with 4 vol. % EG, respectively. The as-prepared and additives-treated PEDOT:PSS films deposited on glass substrates have been investigated by optical spectroscopy, micro-Raman spectroscopy and atomic force microscopy (AFM). The results indicate that structural and morphological changes were induced by the additive processes. By using DMSO and EG treated PEDOT:PSS as a hole transport layer,organic solar cells with a Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC71BM) bulk heterojunction have been fabricated on indium-tin-oxide (ITO) coated glass substrates. The high power conversion efficiency (PCE) of 5.17%, and 5.69%, were observed for PEDOT:PSS hole transport layers treated with DMSO and EG respectively, even though the devices were prepared in air atmosphere.
Ochiai, Shizuyasu,Uchiyama, Masaki,Kannappan, Santhakumar,Jayaraman, Ramajothi,Shin, Paik-Kyun The Korean Institute of Electrical and Electronic 2012 Transactions on Electrical and Electronic Material Vol.13 No.1
Organic solar cell devices were fabricated using poly[9-(1-octylnonyl)-9H-carbazole-2.7-diyl]-2.5-thiophenediyl-2.1.3-benzothiadiazole-4.7-diyl-2.5-thiophenediyl] PCDTBT/ [6,6]-phenyl $C_{71}$ butyric acid methyl ester (PC71BM) active layer deposited by spin coating. Moreover, the relationship between solar cell performance and buffer layer thickness was investigated by spin coating speed and AFM imaging of the buffer layer surface. The performance of the organic solar cell with spin-coated active layer was then evaluated, and the power conversion efficiency of the solar cell was determined to be > 5%.
Effect of Additives on the Structure, Nanomorphology and Efficiency of PCPDTBT: PC71BM Solar Cells
Shogo Imamura,Kumar Palanisamy,Santhakumar Kannappan,Shizuyasu Ochiai 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3
We investigated the effect of additives on the morphology of a poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b0]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):(6,6)-phenyl C<sub>71</sub>-butyric acid methyl ester (PC<sub>71</sub>BM) blended onto a surface of poly (3, 4-ethylendioxythiophene): poly(styrensulfonate)(PEDOT:PSS) to form photoactive films. Films of PCPDTBT: PC<sub>71</sub>BM bulk heterojunctions were prepared by spin-coating from a solution in chlorobenzene (CB) and were processed with and without the addition of 2%, 4%, and 6 vol% 1-chloro naphthalene (CN) or 1, 8-octanedithiol (ODT) as additives. For all samples, the PCPDTBT:PC<sub>71</sub>BM molar ratio was 1:2 (wt%), and the additives in 1 ml were prepared with a concentration of 30 mg of PCPDTBT:PC<sub>71</sub>BM. Optical absorption spectroscopy measurements of the films indicated shifts in the absorption peaks in the range from 500 - 800 nm which was attributed to PCPDTBT. XRay diffraction (XRD) was used to investigate the nature of the molecular stacking in the polymer thin films. Topographic images which were obtained by using an atomic force microscope, of the PCPDTBT:PC<sub>71</sub>BM layers with 2 vol% ODT additive, were found to have the highest surface roughness. The best performing device shows a power conversion efficiency of 2.15% for a 2-vol% ODT additive.
Kunjithapatham Sethuraman,Palanisamy Kumar,Kannappan Santhakumar,Shizuyasu Ochiai,신백균 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.1
Fluorinated copper-phthalocyanine (F<sub>16</sub>CuPc) thin films were prepared by using a vacuum evaporation technique and were applied to <i>n</i>-type organic field-effect transistors (OFETs) as active channel layers combined with a spin-coated polycarbonate thin-film gate insulator. The output characteristics of the resulting <i>n</i>-type OFET devices with bottom-gate/bottom-contact structures were investigated to evaluate the performances such as the field effect mobility (<i>μ<sub>FE</sub></i>), the on/off current ratio (<i>I<sub>on/off</sub></i>), and the threshold voltage (<i>V<sub>th</sub></i>). A relatively high field effect mobility of 6.0 × 10<sup>−3</sup> cm<sup>2</sup>/Vs was obtained for the n-type semiconductor under atmospheric conditions with an on/off current ratio of 1 × 10<sup>4</sup> and a threshold voltage of 5 V. The electron mobility of the n-type semiconductor was found to depend strongly on the growth temperature of the F<sub>16</sub>CuPc thin films. X-ray diffraction profiles showed that the crystallinity and the orientation of the F<sub>16</sub>CuPc on a polycarbonate thin film were enhanced with increasing growth temperature. Atomic force microscopy studies revealed various surface morphologies of the active layer. The field effect mobility of the F<sub>16</sub>CuPc-OFET was closely related to the crystallinity and the orientation of the F<sub>16</sub>CuPc thin film.
Shizuyasu Ochiai,Masaki Uchiyama,Santhakumar Kannappan,Ramajothi Jayaraman,신백균 한국전기전자재료학회 2012 Transactions on Electrical and Electronic Material Vol.13 No.1
Organic solar cell devices were fabricated using poly[9-(1-octylnonyl)-9H-carbazole-2.7-diyl]-2.5-thiophenediyl-2.1.3-benzothiadiazole-4.7-diyl-2.5-thiophenediyl] PCDTBT/ [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) active layer deposited by spin coating. Moreover, the relationship between solar cell performance and buffer layer thickness was investigated by spin coating speed and AFM imaging of the buffer layer surface. The performance of the organic solar cell with spin-coated active layer was then evaluated, and the power conversion efficiency of the solar cell was determined to be > 5%.