成果報告書詳細
管理番号20120000000148
タイトル*平成23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2012/6/20
報告書年度2011 - 2011
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

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) films as an infrared-sensitive material. In this work, we pursue the epitaxial growth of crystalline Ge layers on single crystalline Si substrates due to solid phase crystallization (SPC).
Amorphous Ge (a-Ge) films were prepared on single crystalline Si substrates by electron beam evaporation. The Si substrates had p, n and intrinsic (i) conduction types with (100) and (111) crystalline orientations. The film thickness of a-Ge was 10000 A. SPC was conducted by thermal annealing for 10 hrs. from 375?C to 475?C in argon (Ar) atmosphere. Crystallinity and crystal orientation were evaluated by the Raman spectroscopy and the X-ray diffraction (XRD). The cross-section of c-Ge films was observed by the Transmission Electron Microscope (TEM) and the Low Energy Electron Diffraction (LEED). The defects in the epitaxial Ge layers were evaluated by conductive atomic force microscopy (C-AFM).
The epitaxial growth was successfully done on n-type Si with (100) orientation at SPC temperature of 425-475 ?C. The n-type Si substrate with (100) orientation is the most suitable for epitaxial crystal growth of Ge due to the SPC, and the epitaxial growth of at least 10000A is confirmed by XRD, TEM and LEED. But other orientations than substrate one appear in the Ge grown on the other Si substrates, and become more obvious at higher temperature. However, the continuous lattice images are observed by Cross-sectional TEM images in the samples which show other orientations in the XRD and LEED images, and random crystal growth does not occur in these samples.
In the epitaxial Ge films grown on n-type Si (100) substrate, many low resistance spots are observed by C-AFM, and it is suggested that the current leak passes are formed by Ge defects such as dislocation, point defect and so on. Because dangling bonds of Ge strongly capture electrons and cause holes, significant p-type conduction paths appear along these defects. Applying the Ge films to photovoltaic devices, these defects must be eliminated or inactive. We recently found that high-pressure water vapor treatment is effective to reduce the Ge dangling bond defects. This might be helpful to realize device-quality crystalline Ge films.
This result proves that single crystalline Ge films can be fabricated on Si substrate by the SPC, and it is expected that the SPC and defect passivation techniques contribute to achieve the goal of our project.
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