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Keisuke Ohdaira,Takafumi Oikawa,Koichi Higashimine,Hideki Matsumura 한국물리학회 2016 Current Applied Physics Vol.16 No.9
The epitaxial growth of silicon (Si) films during the catalytic chemical vapor deposition (Cat-CVD) of intrinsic amorphous Si (i-a-Si) passivation films on crystalline Si (c-Si) wafers is suppressed by the oxidation of c-Si surfaces simply by dipping the c-Si wafers in hydrogen peroxide (H2O2). This oxidation treatment is also effective for (111)-oriented c-Si surfaces particularly at high a-Si deposition temperatures. The suppression of the epitaxial growth leads to the better effective minority carrier lifetime (teff) of c-Si wafers passivated with Cat-CVD i-a-Si films. SHJ solar cells show remarkably high open-circuit voltage (Voc) exceeding 0.7 V. These results clearly show the effectiveness of the insertion of SiOx layers on the improvement in Cat-CVD a-Si/c-Si interfaces.
Keisuke Ohdaira,Hiroyuki Takemoto,Takuya Nishikawa,Hideki Matsumura 한국물리학회 2010 Current Applied Physics Vol.10 No.3
Polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of precursor a-Si films are found to hardly lose hydrogen (H) atoms during crystallization and keep the initial H concentration on the order of 1021/㎤. Short annealing duration and sufficient Si film thickness would lead to the suppression of H desorption. A characteristic lateral crystallization mechanism, referred to as explosive crystallization (EC), may also contribute to the prevention of H desorption due to rapid lateral heat diffusion into neighboring a-Si. Poly-Si films after annealing under N2 or forming gas ambient shows remarkably long minority carrier lifetime compared to untreated films, indicating effective defect termination by H atoms remaining in the poly-Si films.
Takuya Nishikawa,Keisuke Ohdaira,Hideki Matsumura 한국물리학회 2011 Current Applied Physics Vol.11 No.3
The electrical properties of polycrystalline silicon (poly-Si) films formed from amorphous silicon (a-Si)films by flash lamp annealing (FLA) are investigated by Hall effect measurement. The impurity-doping concentration dependences of resistivity, carrier density, and Hall mobility of such flash-lamp-crystallized (FLC) poly-Si films show the effect of carrier trapping at grain boundaries (GBs). Potential barrier height formed at GBs, estimated from the temperature dependences of Hall mobility and electrical conductivity, decreases with an increase in doping concentration, due to the complete filling of trapping states at GBs. The density of trapping states at GBs is estimated to be on the order of 10^12 cm^-2 from such barrier heights, which is almost equivalent to those of poly-Si films prepared by other techniques such as solid-phase crystallization or laser annealing of a-Si films.
Application of crystalline silicon surface oxidation to silicon heterojunction solar cells
Takafumi Oikawa,Keisuke Ohdaira,Koichi Higashimine,Hideki Matsumura 한국물리학회 2015 Current Applied Physics Vol.15 No.10
We study the effect of ultra-thin oxide (SiOx) layers inserted at the interfaces of silicon heterojunction (SHJ) solar cells on their open-circuit voltage (VOC). The SiOx layers can be easily formed by dipping c-Si into oxidant such as hydrogen peroxide (H2O2) and nitric acid (HNO3). We confirm the prevention of the undesirable epitaxial growth of Si layers during the deposition of a-Si films by the insertion of the ultrathin SiOx layers. The formation of the SiOx layers by H2O2 leads to better effective minority carrier lifetime (teff) and VOC than the case of using HNO3. c-Si with the ultra-thin SiOx layers formed by H2O2 dipping, prior to deposition of a-Si passivation layers, can have high implied VOC of up to ~0.714 V.