Pressure Dependence of a Deep Excitonic Level in Silicon
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PRESSURE DEPENDENCE OF A DEEP EXCITONIC LEVEL IN SILICON* G.A. Northrop and D.J. Wolford IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598.
ABSTRACT Certain optically active defects in silicon provide a unique opportunity to observe, in detail, the effect of hydrostatic pressure on a deep level. We present a photoluminescence (5 - 100K) study of one such defect, the I radiation-damage center, under high hydrostatic pressures (1-50 kbar). While the energy variation of this level indicates the expected mutli-band nature typical of a deep level, a severe and continuous reduction in the observed luminescence intensity was also observed. Temperature dependence, time resolved photoluminescence, and photoluminescence excitation spectroscopy are employed to attempt to discern the mechanism involved. INTRODUCTION Over the last 10 years a number of defects have been reported in silicon which exhibit strong no-phonon lines in photoluminescence, often with remarkably high efficiency [1]. These are deep excitonic levels that show some lattice coupling (vibronic side bands) but have a strong enough no-phonon line that makes the precise energy level clearly identifiable. Some are complexes produced by radiation damage, followed by low temperature annealing, of which most involve impurities such as oxygen and carbon normally found in CZ silicon. Another group occurs when transition metals, such as iron and chromium, are diffused into Si. Most of these are assumed to be dopant - transition metal complexes. A third group can be formed by rapid thermal quenching of heated In or TI doped Si. As a group, these defects are well suited to the study of the effects of high pressure on deep levels in silicon due to their strong signatures and narrow linewidths. The I1 center [2], produced by radiation damage, was selected for this study primarily due to its strong luminescence, and the fact that it can be produced easily in high purity silicon. Although its microscopic structure is not known, its occurrence doesn't correlate with any impurity, thus, it is likely a complex of intrinsic defects produced by the radiation damage. It is most efficiently produced by ion or neutron bombardment, but can also be produced by other forms of radiation. Magnetic field and uniaxial stress measurements have shown that the I1 ground state is non-degenerate, and that the defect has C3, symmetry [3-5]. It has a total binding energy of 137 meV, and the temperature dependence of the PL intensity has an Arhenius quench energy (~ thermal binding energy) of about 50 meV [4]. PHOTOLUMINESCENCE ENERGY VS. PRESSURE 2 The samples used in this study were taken from boron doped (~10i5 cm- ) CZ grown wafers. These wafers were damaged by implantation with 3xl0' 2/cm 2 Si÷, at 50 keV, and then annealed at 200 'C to produce the I1 centers. Chemical etch profiling of samples prepared this way indicates that the I centers are confined to within 0.3 Am of the surface, however, there is no good estimate of the defect density created this way. A thinned piece of
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