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.
Highlights
Solar cells that use nanomaterials have attracted interest for their potential as ultra-high efficiency solar cells [1]
Structure of the Si-QDSL is almost uniform in the depth direction
Surface roughness is modeled using the effective medium approximation (EMA) model for ellipsometry analysis; the estimated Ts reflects surface roughness, and no damaged layer exists on the surface. These results clearly indicate that reactive ion etching (RIE) can remove the damaged layer without additional damage to the sample; RIE is the key to improve the film quality of Si-QDSLs and the p/i interface in Si-QDSL solar cells
Summary
Solar cells that use nanomaterials have attracted interest for their potential as ultra-high efficiency solar cells [1]. 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 [3,4,5]. 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).
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