成果報告書詳細
管理番号20140000000715
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(擬単結晶固相成長技術)
公開日2015/4/24
報告書年度2013 - 2013
委託先名東海大学
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 semi-crystalline Si-related materials by solid phase crystallization(FY2008-2014) FY2013 Annual Report

Infrared-sensitive photovoltaic films are necessary for bottom cells of multi-junction cells for obtaining extremely high efficiency thin film solar cells. We have investigated crystalline germanium (Ge) and silicon-germanium (SiGe) films as infrared-sensitive materials. We pursue the epitaxial-like growth of crystalline Ge and SiGe layers on single crystalline Si (c-Si) substrates due to solid phase crystallization (SPC). In the previous reports, we found that impurities in amorphous Ge (a-Ge) precursors included from the atmosphere disturb the epitaxial-like growth and that the epitaxial-like growth is affected by the crystalline orientations and conductive types of Si substrates. In this report, we investigated the influence of Si substrates on the epitaxial-like growth of Ge and discussed about the crystallization processes. We also investigated the epitaxial-like growth of SiGe from amorphous SiGe (a-SiGe) precursors on c-Si substrates with wider energy gaps than 0.9 eV based on the results of Ge in order to achieve the final target of this project.
A-Ge precursors were prepared on n- and p-type c-Si substrates with (100) and (111) orientations by electron beam (EB) evaporation. The SPC was done at 400°C to 475°C in Ar atomosphere for 1-10 hrs. A-SiGe precursors were prepared on n-type c-Si substrates with (100) orientations by simultaneous evaporation of Ge with Knudsen cell (K-cell) and Si with electron beam (EB) evaporation. The SPC was done at 700°C to 100°C in the vacuum for 10 hrs. The crystallinity and crystal orientation of the SPC samples were evaluated by Raman spectroscopy and X-ray diffraction (XRD), respectively.
N-type (100) Si substrates are the most suitable for the epitaxial-like growth of Ge and the epitaxial-like growth can be conducted with relatively high impurity concentration. But the epitaxial-like growth on n-type (111) and p-type (100) Si substrates is disturbed by the impurity incorporation. Random crystallization appears on p-type (111) Si substrates even at low impurity concentration. It was found that the difference among the substrates is caused by different velocity of the preferential crystalline growth. The velocity of the epitaxial-like growth is the fastest on n-type (100) Si substrates, and becomes slower in the order of n-type (111) and p-type (100) Si substrates. Therefore, the random crystalline growth appears on the n-type (111) and p-type (100) Si substrates when the random crystalline formation is enhanced at high impurity concentration. On the other hand, the random crystalline formation occurs earlier than the preferential growth on the p-type (111) Si substrates. Available electrons to form covalent bonds are less in the p-type Si, so it might take more time to start the preferential growth. The preferential growth for (100) direction is probably faster than that for (111) direction because a number of dangling bonds on the (100) surface is more than on the (111) surface. The two conditions are both bad in the growth on the p-type (111) Si, so the preferential growth following the substrate direction does not occur.
Based on the results of Ge, we also conducted the epitaxial-like growth of SiGe to attain the final target. The SiGe has wider energy gap than 0.9 eV and relatively high light absorption coefficients when the Ge fraction is 50-75%, and then is suitable materials for thin film multi-junction cells. The epitaxial-like growth is successfully obtained in the SiGe with both 50% and 75% Ge fractions on n-type (100) Si substrates. But the rocking curves of XRD measurements shows much wider peaks compared with single crystalline Ge and Si. Probably, the crystallized SiGe has mosaic structures of small crystalline domains with slightly offset crystalline planes.
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