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Boussairi Bouzazi,Nobuaki Kojima,Yoshio Ohshita,Masafumi Yamaguchi 한국물리학회 2013 Current Applied Physics Vol.13 No.7
Deep level transient spectroscopy (DLTS) was deployed to study the evolution, upon electron irradiation and hydrogenation of GaAsN grown by chemical beam epitaxy, of the main nitrogen-related nonradiative recombination center (E1), localized at 0.33 eV below the bottom edge of the conduction band of the alloy. On one hand, the electron irradiation was found to enhance the density of E1 depending on the fluence dose. On the other hand, the hydrogenation was found to passivate completely E1. Furthermore,two new lattice defects were only observed in hydrogenated GaAsN films and were suggested to be in relationship with the origin of E1. The first defect was an electron trap at average thermal activation energy of 0.41 eV below the CBM of GaAsN and was identified to be the EL5-type native defect in GaAs,originating from interstitial arsenic (Asi). The second energy level was a hole trap, newly observed at average thermal activation energy of 0.11 eV above the valence band maximum of the alloy and its origin was tentatively suggested to be in relationship with the monohydrogenenitrogen (NeH) complex. As the possible origin of E1 was tentatively associated with the split interstitial formed from one N atom and one As atom in single V-site [(NeAs)As], we strongly suggested that the new hole trap took place after the dissociation of E1 and the formation of NeH complex.
터널 산화막 전하선택형 태양전지를 위한 인 도핑된 비정질 실리콘 박막의 패시베이션 특성 연구
이창현,박현정,송호영,이현주,Yoshio Ohshita,강윤묵,이해석,김동환 한국태양광발전학회 2019 Current Photovoltaic Research Vol.7 No.4
Recently, carrier-selective contact solar cells have attracted much interests because of its high efficiency with low recombination current density. In this study, we investigated the effect of phosphorus doped amorphous silicon layer’s characteristics on the passivation properties of tunnel oxide passivated carrier-selective contact solar cells. We fabricated symmetric structure sample with poly-Si/SiOx/c-Si by deposition of phosphorus doped amorphous silicon layer on the silicon oxide with subsequent annealing and hydrogenation process. We varied deposition temperature, deposition thickness, and annealing conditions, and blistering, lifetime and passivation quality was evaluated. The result showed that blistering can be controlled by deposition temperature, and passivation quality can be improved by controlling annealing conditions. Finally, we achieved blistering-free electron carrier-selective contact with 730mV of i-Voc, and cell-like structure consisted of front boron emitter and rear passivated contact showed 682mV i-Voc.
송인설,이현주,이상원,배수현,현지연,강윤묵,이해석,Yoshio Ohshita,Atsushi Ogura,김동환 한국물리학회 2018 Current Applied Physics Vol.18 No.11
We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of AlOx- and AlOx/SiNx:H stack-passivated pyramid textured p+-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured p+-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of AlOx layers on pyramid textured p+-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance (RSW) from ∼2.5 to ∼3.7% for the AlOx/SiNx:H stack-passivated pyramid textured p+-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ∼60 and ∼100 Ω/sq p+-emitters is reduced by 0.8 and 0.6 mA/cm2, respectively under front p+-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with∼60 and∼100 Ω/sq p+-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ∼100 Ω/sq p+-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.
Properties of Chemical Beam Epitaxy grown GaAs0.995N0.005 homo-junction solar cell
Boussairi Bouzazi,Kenichi Nishimura,Hidetoshi Suzuki,Nobuaki Kojima,Yoshio Ohshita,Masafumi Yamaguchi 한국물리학회 2010 Current Applied Physics Vol.10 No.2
The minority carrier diffusion length in Chemical Beam Epitaxy (CBE) grown GaAs0.995N0.005 based homojunction solar cell was estimated and found to be L = 0.08 lm. In addition, the majority carrier traps in Nvarying unintentionally doped p-type GaAsN samples grown by CBE were investigated using Deep Level Transient Spectroscopy (DLTS) technique. Five hole traps, HC1–HC5, were detected, where HC2 and HC5coexist in all samples. These two hole traps were suggested to be a N-related defect and the double donor state of EL2, respectively.
Light induced recombination center at SiO2/Si interface by the reactive plasma deposition
Tomohiko Hara,Taichi Tanaka,Kazuhito Nakagawa,Yuki Isogai,Takefumi Kamioka,Yoshio Ohshita 대한금속·재료학회 2021 ELECTRONIC MATERIALS LETTERS Vol.17 No.5
Effect of lights with various wavelength on the defect generation in reactive plasma deposition (RPD) process is studiedusing capacitance–voltage analysis. Indium-tin oxide (ITO) deposition by RPD dramatically decreases the minority carrierlifetime and deteriorates the solar cell performances. The wavelength of light which arrives at the SiO2/Si interface andSi crystal is controlled by varying the SiO2thickness in SiO2/Si samples. Thick SiO2layer with above 10 nm prevents thepenetration of many ions into the SiO2/Si interface layer, and the only effects of light wavelength on the defect formation areobtained. When SiO2thickness are 10–600 nm, a large number of defects of the order of 1012eV−1 cm−2, mid gap energyof Si, are generated by ITO-RPD independent of SiO2thickness. These defects are expected to be recombination centers. These SiO2thicknesses are enough thick to completely absorb the light below-110-nm-wavelength. The results suggest thatthe light of longer wavelength than 110 nm mainly contributes to the defect formation in RPD process. On the other hand,in the case of 500 μm thick SiO2,the generated defects are significantly decreased by one order of magnitude (or decreasedto the order of 1010eV−1 cm−2) small amount of defect is generated. This thick SiO2prevents the penetration of light withbelow 180 nm wavelength into the Si. Therefore, the light with around 110–180 nm wavelength, which are generated by Arand/or O2plasma in RPD process, mainly forms the recombination-active defects.
Relation between N–H complexes and electrical properties of GaAsN determined by H implantation
Jong-Han Lee,Hidetoshi Suzuki,Xiuxun Han,Katahiko Honda,Tomohiro Tanaka,Jong-Ha Hwang,Boussairi Bouzazi,Makoto Inagaki,Nobuaki Kojima,Yoshio Ohshita,Masafumi Yamaguchi 한국물리학회 2010 Current Applied Physics Vol.10 No.3
We investigated the relation between N–H complexes and the electrical properties of GaAsN, which is a potential material for fabricating super-high-efficiency multi-junction tandem solar cells. In order to separate the effect of other residual carrier such as carbon in a GaAsN film on the electrical properties, hydrogen (H) ions were implanted into GaAsN grown by chemical beam epitaxy (CBE) and then rapid thermal annealing from 250 to 650 ℃ was carried out. Two N–H complexes related to local vibrational modes (LVMs) in GaAsN were observed at 3098 and 3125 cm-1. With an increasing annealing temperature,the integrated peak intensity of the 3098 cm-1 peak (I3098) decreased, while that of the 3125 cm-1 peak (I3125) increased. This indicates that N–H complexes related to the 3125 cm-1 peak are thermally more stable than those related to the other peak. The hole concentrations and mobilities exhibited an increasing trend until an annealing temperature of 550 ℃ was reached. Their increases are attributed to the removal of donor-type defects. It is suggested that the N–H complexes related to the 3098 cm-1 peak are electrically active, while those giving the 3125 cm-1 peak are inactive.