成果報告書詳細
管理番号20140000000731
タイトル*平成25年度中間年報 新エネルギー技術研究開発 革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)高度秩序構造を有する薄膜多接合太陽電池の研究開発(ナロー/ワイドギャップ、高性能透明導電膜、有機単結晶)
公開日2015/5/16
報告書年度2013 - 2013
委託先名国立大学法人東京工業大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title: Development of epitaxial growth of single crystalline Ge and related thin films (FY2008-FY2014) FY2013 annual report

<2-1-2 Development of SiGe-based bottom cells>
We studied the effect of temperature on quality of epi-SiGe films, in particular, at the temperature region from 290oC to 360oC, where the gas phase reaction is suppressed and the surface reaction on Si substrate plays a major role for film deposition. We use Ar for diluent instead of He because of small heat conductivity. The growth rate of the film had a peak at around 310oC and re-increased from around 350oC. Judging from Raman spectra and surface morphology evaluated by AFM measurement, the optimized temperature for the film deposition was at 300oC, and the film deposited at 300oC exhibited high crystallinity and Ge composition of 99%, the best surface morphology (RMS: 1.1 nm). Its threading dislocation density was estimated to be 2×107cm2.
In order to improve the film quality, we studied the effect of thermal annealing in the presence of hydrogen. The XRDω-2θ scan for (004) peak indicated that the film quality was improved and Ge composition decreased from 99& to 95.2% after the thermal annealing at 650oC for 30 min and H2 pressure of 104 Pa. The TEM study of the films revealed that misfit dislocation at the Ge/Si interface was confined at the interface and threading dislocation density was much decreased to be 4.5×105cm2 from 8×106cm2.
In in situ-doping with phosphine for carrier compensation in epi-SiGe films, we found that n-type doping with phosphine could be achieved in the RT-CVD without degradation of film quality up to 750ppm, and found the doping concentration of phosphine at this condition to be 0.5 ppm for hole concentration of epi-SiGe films.

<2-2-2 Development of nanopatterned glass substrate and high performance TCO for organic crystal solar cells>
In this year, we performed atomic-scale surface patterning with a vertical resolution of approximately 0.3 nm on a glassy thermoplastic polymer of poly(methyl methacrylate) (PMMA) sheet (10×10 mm2) by thermal nanoimprinting using an atomically stepped sapphire template (α-Al2O3 single crystal). The sapphire mold with (10-12) r-plane exhibited regularly arranged straight steps with a uniform height of approximately 0.31 nm. The template nanopattern could be transferred onto the surface of the PMMA sheet under the imprinting conditions of 0.2 MPa load for 300 s at 140°C. Atomic stairs with approximately 0.26-nm-high straight steps and approximately 600-nm-wide terraces were formed on the PMMA surface.

<3-2-3 Development of top cell based on compound semiconductors>
In this year, first, we explored PLD conditions for fabrication of p-type SnS epitaxial and stoichiometric films. Using argon / hydrogen sulfide premixed gas as a sulfur source was important to maintain the chemical stoichiometry in the films. The conditions for obtaining single phase SnS films were limited to a narrow substrate temperature range, T(sub), around 400 degrees centigrade and the epitaxial films prepared at T(sub) = 400 degrees centigrade and P = 10 Pa shows good S/Sn ratio (0.997) and high Hall mobility (37 cm2/Vs). Then, we have also optimized Cd/Ga ratios of a new n-type amorphous oxide semiconductor, amorphous Cd-Ga-O (a-CGO) films. The band gap energy of Cd rich films (Cd/(Cd+Ga) = 82 %) was estimated to be 2.3 eV. On the other hand, the conduction band minimum of the Ga rich film (Cd/(Cd+Ga) = 11%) was shallower than those of amorphous In-Ga-Zn-O (a-IGZO) and ZnO, indicating that large open circuit voltage of the Ga rich a-CGO / Cu2O solar cell would be expected.
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