Structural Investigation of Electrochemically Etched Silicon
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STRUCTURAL INVESTIGATION OF ELECTROCHEMICALLY ETCHED SILICON 5 5 4 B.J. Heuser, 1 S. Spooner, 2 .t C.J. Glinka, 3 D.L. Gilliam, N.A. Winslow and M.S. Boley
IUniversity of Missouri Research Reactor Center, Columbia. MO
2 .tNational Center for Small-Angle Scattering Research, Oak Ridge National 3 Reactor Radiation Division, National Institute of Standards and Technology, 4
Laboratory, Oak Ridge, TN Gaithersburg, MD
Lincoln University, Jefferson City, MO Department of Physics and Astronomy, University of Missouri, Columbia, MO
5
ABSTRACT Small-angle neutron scattering (SANS) measurements of four electrochemically etched, porous silicon (PS) samples have been performed over a wide wavevector transfer (Q) range. The intermediate to high Q results can be modeled with a non-particulate, random phase model. Correlation length scales on the order of 1 to 2 nm thought to characterize the PS skeleton have been deduced from the SANS data. The microstructural anisotropy was studied tilting two of samples exhibited an asymmetric the samples with respect to the neutron beam. These scattering pattern at intermediate Q (0.1 • Q < 0.6 nm- 1 ) in this condition. Photoluminescence spectra from all four samples have been recorded as well. A correlation appears to exist between the SANS and photoluminescence measurements. An x-ray diffraction measurement of one sample demonstrates that the PS layer retains the silicon lattice structure. Significant peak broadening is observed that we interpreted as a quasi-particle size effect. The PS particle size calculated from the x-ray diffraction measurement is equal to the correlation length obtained
in the SANS measurement.
INTRODUCTION The discovery of a form of Si with a photoluminescence efficiency much higher than that of bulk Si has led to a flurry of research activity. This unusual form of Si is created during electrochemical etching of oriented single crystal Si in hydrofluoric acid under a variety of conditions. The resultant material is very porous and often appears red in color. Electrical, photoluminescence, and structural properties of electrochemically etched, porous silicon (PS) have been extensively investigated in the past few years. Two suggested explanations for the dramatic increase in photoluminescence efficiency involve i) the quantum confinement of charge carriers in very small structures (on the order of a nanometer) created during etching [1] or ii) the contamination of internal surfaces by foreign elements such as hydrogen and oxygen [2]. Complete understanding of the PS photoluminescence behavior will require accurate structural information. To this end, the goal of the work presented here was to determine bulk structural parameters characteristic of the PS material investigated. Four PS samples were characterized with SANS, two over a wide wavevector transfer range. Microstructural anisotropy and vertical uniformity for selected samples were investigated as part of this study. Photoluminescence spectra also were obtained for each sample, and a correlation betwe
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