Strain Induced Intrinsic Quantum wells as the Origin of Broad Band Photoluminescence in Silicon Containing Extended Defe
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STRAIN INDUCED INTRINSIC QUANTUM WELLS AS THE ORIGIN OF BROAD BAND PHOTOLUMINESCENCE IN SILICON CONTAINING EXTENDED DEFECTS H. WEMAN* AND B. MONEMAR Department of Physics and Measurement Technology, Linkoping University, S-581 83 Linktping, SWEDEN *Present address: Center for Quantized Electronic Structures (QUEST), University of California at Santa Barbara, Santa Barbara, California, 93 106, USA ABSTRACT A new recombination mechanism occuring in semiconductors containing extended defects is presented. The model is based on experimental data both from hydrogen plasma treated silicon, containing extended defects like platelets, and from oxygen precipitated silicon. The broad photoluminescence bands from these samples are attributed to the heavily damaged regions surrounding the extended defects, where electrons and holes can be localized in the strain-induced potential wells. From a theoretical calculation it is shown that the compressive strain field surrounding [111] and [100] platelets are sufficient to cause a local band gap reduction of as much as 0.3 eV, consistent with the experimental data. INTRODUCTION Low-temperature photoluminescence (PL) studies of defects in silicon have become a field of great interest in the past fifteen years, as recently reviewed by Davies [1]. Most of the work has been concentrated on bound exciton spectra of various impurities in the crystal, introduced both intentionally (by doping) or non-intentionally (process induced). The PL from these centres usually gives rise to very sharp PL lines whereby the properties of the defects can be analyzed quite accurately. However in some cases broad featureless PL bands are observed which have been almost neglected [2-4]. It is the purpose of this paper to present a model which can explain the origin of these broad PL bands which are based on the local strain fields that surrounds the defects, as we tentatively suggested recently [5]. These broad bands are commonly observed in samples where more extended defects are seen. This includes oxygen precipitated [2,4], antimony precipitated [3] and hydrogen plasma treated silicon [5]. Most of our data presented in this paper are based on the experimental data from hydrogen plasma treated silicon where the geometry and dimensions of the extended defects (platelets, gas bubbles) are well known from transmission electron microscopy (TEM) viewgraphs. It has been shown that these platelets are commonly occuring as [111] planar defects with an extension of about 100 A causing a 20 to 30 % dilation of the silicon interplanar separation [6]. EXPERIMENTAL RESULTS The details of the experimental setup used in the PL experiments can be found elsewhere [4,5]. Typical broad PL bands that we will be discussing are shown in Figs. I and 2. The PL spectrum in Fig. 1 is taken at 2 K of a boron doped Si sample reactive ion etched (a), or plasma etched (b), in a 25 mTorr deuterium plasma for 10 min. The broad PL bands peaking at 0.9 eV with a halfwidth of 100 meV (FWHM), Fig. I (a), and 0.92 eV with a halfwidth of 75 m
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