Light-Emitting nm-Size Silicon Using Electrochemical Anodization and Oxidation
- PDF / 1,410,050 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 78 Downloads / 223 Views
LIGHT-EMITTING nm-SIZE SILICON USING ELECTROCHEMICAL ANODIZATION AND OXIDA:1ON
TOSHIMICHI ITO, TOSHIMICHI OHTA, KENJI MOTOI, OSAMU ARAKAKI AND AKIO HIRAKI Osaka University, Department of Electrical Engineering, Suita, Osaka 565, Japan.
ABSTRACT Porous silicon oxidized by thermal, anodic and plasma processes has been investigated mainly using transmission microscopy, ion scattering techniques for compositional depth analysis (including H) and photoluminescence (PL) measurements. Suitable thermal oxidation of PS can increases in PL peak energy: the largest peak energy attained in the present study is 2.6eV (475nm). In the case of anodic oxidation. PL excitation spectra measured suggest the presence of some effect other than the quantum confinement effect at the initial oxidation stage while the latter may be effective at the subsequent anodic oxidation stage and in the thermal oxidation process. Electroluminescence was also observed from the oxidized porous silicon. INTRODUCTION Many investigations have been performed on anodically produced porous silicon (PS) since a report by Canham' on strong visible light emission. 2.3 Light-emitting as-prepared PS is unstable in strucuture due to its very fine structure with many micropores. Hydorgen-covered surfaces of the pores easily incorporate oxygen atoms mainly into Si backbond sites during even a short-period air storage of as-prepared PS. 4 This property is one of problems arizing whenever PS is used. In order to prevent the structural instability of PS, ' slight oxidation of PS has successfully been utilized for epitaxial growth of Si on PS substrates retaining the original crystallinity of Si wafers.
6
Similar oxidation can be employed to stabilize the PS structure and to thin skeletonized Si. We have reported on the effectiveness of the thermal oxidation of PS on blue shifts of optical properties. ',' In that work only red photoluminescence was observed using PS films with mesopores. Subsequently, thermal oxidations of PS with micropores have been studied.9'," In the present paper, PS with micropores oxidized by means of thermal and anodical oxidation methods as well as plasma oxidation technique has intensively been studied. Photoluminescence with a peak wavelength as short as 475nm has been observed. Furthermore, the study on PS with varying compositions at the Si internal surfaces may give information on the origin of the light emission which has not clearly been determined yet. EXPERIMENTAL P-type Si(lO0) wafers (resistivity p= 5-30Qcm) and Si(ll1) wafers (p= 0.7-1.3 Qcm) were anodized in a HF-ethanol solution (HF:H 2 0:C 2 H6 OH =2 1:1:2) for periods of 20-180 s. Anodic current ranged from 20 to 100 mA/cm . Some samples were illuminated by a tungusten lamp (260001x) during the anodization. PS films thus obtained were subjected to subsequent different oxidations. Thermal oxidation was performed at 600-900 °C in a resistively-heated furnace under a gas flow of dry oxygen at a rate of 1.0 P/min. For some of those specimens, vacuum annealing followed the oxidati
Data Loading...
