Optical Properties of Deuterium Terminated Porous Silicon
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Takahiro Matsumoto*, Yasuaki Masulmoto*, and Nobuyoshi Koshida** *Single
Quantum Dot Project, ERATO, Japan Science and Technology Corporation, 5-9-9
Tokodai, Tsukuba 300-26, Japan, [email protected] **Division of Electronic and Information Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan
ABSTRACT We have studied the optical properties of deuterium-terminated porous silicon. The photoluminescence spectrum was different from that of usual hydrogen-terminated porous Si despite porous Si showing both the same structure and the same absorption spectrum. These results indicate that the surface vibrat:ion of terminated atoms couples to the quantum confined states. INTRODUCTION Porous silicon formed by electrochemical anodization has attracted a lot of interest recently because it exhibits strong visible photoluminescence at room temperature [1]. Although a great deal of effort has been made to elucidate the origin of the photoluminescence, much of the uncertainty still remains due to the difficulty of physical characterization in nanometer structure of porous Si. Isotopes are powerful tools for searching molecular terminations, kinetics of atoms or molecules, or the interaction between nuclei and extra nuclear electrons. Especially, hydrogen and its isotope are widely used to study the surface structure [2] and the diffusion of hydrogen in crystalline Si [3]. A huge amount of terminating hydrogen is supplied from hydrofluoric acid (HF) in porous Si [4,5], therefore by using isotope electrolyte such as deutrofluoric (DF) acid, the surface terminations can be changed from hydrogen to deuterium. In this paper, we report the optical properties of isotope terminated porous Si. We have fabricated deuterium-terminated porous Si (D-PS) using DF-ethanolD6 solution (DF:C 2D5 OD:D 2 0=1:1:2). We have characterized the D-PS together with the usual hydrogenterminated porous Si (H-PS) by Raman spectroscopy and transmission electron microscope (TEM) analysis. In spite of the same nanometer structure and the same optical absorption spectrum for both samples, D-PS shows shorter PL than that of H-PS. These results can be analyzed by considering both the bandgap upshift due to the quantum size effect and the energy reduction due to the coupling of the confined carriers to the surface vibration of terminated atoms on nanocrystals. 449 Mat. Res. Soc. Symp. Proc. Vol. 452 0 1997 Materials Research Society
EXPERIMENTAL DETAILS AND RESULTS Hydrogen-terminated porous Si (H-PS), and deuterium-terminated porous Si (D-PS) were formed by electrochemical anodizations. The H-PS was fabricated in the dark to avoid oxidation using HF-ethanol solution (HF:H 20:C 2H 5 OH=l:1:2) by applying positive bias to a p-type 3-5 f2cm Si substrate at various current densities in the range from 20 mA/cm 2 to 100 mA/cm 2 . (Samples fabricated with high current densities show wide bandgap energy [6].) The D-PS were also fabricated under the same conditions except for the use of DF-ethanol-D6 solution (DF:C 2D 5 OD:D 2
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