Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorp
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NANO EXPRESS
Open Access
Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix Shigeru Yamada1*, Yasuyoshi Kurokawa1, Shinsuke Miyajima1 and Makoto Konagai1,2
Abstract We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm−3 to 3.7 × 1017 cm−3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching. Keywords: Silicon quantum dot; Hydrogen plasma treatment; Defect density; Hydrogen diffusion PACS: 61.46.Hk; 66.30.Pa; 68.65.Hb; 81.65.Cf
Background Solar cells that use nanomaterials have attracted interest for their potential as ultra-high efficiency solar cells [1]. The conversion efficiency limit of a single-junction solar cell strongly depends on the band gap of the absorber layer, which is known as the Shockley-Queisser limit [2]. To overcome the efficiency limit, various types of quantum dot solar cells, such as quantum size effect type, intermediate band type, and multiexciton generation type, have been proposed [3-5]. The quantum size effect type utilizes the phenomenon that the band gap of a material can be tuned by controlling the diameter of quantum dots, including the periodically arranged narrow-gap quantum dots in a wide-gap dielectric matrix. The fabrication of an amorphous silicon dioxide (a-SiO2) matrix including size-controlled silicon quantum dots (Si-QDs) was reported by Zacharias et al. [6]. The size-controlled Si-QDs can be formed by annealing a superlattice with silicon-rich silicon oxide layers and stoichiometric silicon oxide layers, which is called a silicon quantum dot superlattice structure (Si-QDSL). Since this * Correspondence: [email protected] 1 Department of Physical Electronics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan Full list of author information is available at the end of the article
report was published, silicon quantum dots embedded in various wide-gap materials, such as amorphous silicon carbide (a-SiC), amorphous silicon nitride (a-Si3N4), and hybrid matrices, have been reported [4,7-11]. Further, the quantum size effect can be observed from the measurement of photoluminescence spectra or absorption coefficients [12-14]. The Bloch carrier mobility in a Si-QDSL with an a-SiC matrix is higher than that in a Si-QDSL with an a-SiO2 or an a-Si3N4 matrix [15]. The barrier height between a-SiC and Si quantum dots is lower than those of the other two materials, resulting in the easy formation of minibands [16]. Moreover, the crystallization temperature of a-SiC is lower than those of the other materials. Therefore, in this study, we focu
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