Fermi Resonance Effects on the Vibration Modes of Hydrogen-Passivated Boron in Silicon
- PDF / 480,160 Bytes
- 9 Pages / 420.48 x 639 pts Page_size
- 72 Downloads / 187 Views
FERMI RESONANCE EFFECTS ON THE VIBRATION MODES OF HYDROGEN-PASSIVATED BORON IN SILICON C.D. WATKINS*, W.B. FOWLER*, G.G. DELEO*, M. STAVOLA*, D.M. KOZUCH*, S.J. PEARTON** AND J. LOPATA** * Department of Physics, Lehigh University, Bethlehem, PA, 18015 ** AT&T Bell Laboratories, Murray Hill, NJ, 07974
ABSTRACT 10B
-
11
B
isotope
shifts
have
been
reported
recently
for
the
vibrational frequencies of hydrY6en (H 1 1 and its isotope deuterium (D) in the H-B complex in silicon. The D- B - D B shift was found to be anomalously large. We show that this effect finds a natural explanation in a phenomenon called "Fermi resonance", arising from a weak anharmonic coupling between the second harmonic of the transverse B vibration and the longitudinal D vibration. We first present a simple classical explanation of the effect in terms of a "parametric oscillator", or a child pumping a swing. We then outline a simple quantum mechanical treatment that provides a satisfactory quantitative explanation of the results. Our calculations also predict infrared absorption at the bofun second harmonic frequencies. These are observed for both B and B with intensities and polarization as predicted, providing direct confirmation of the interpretation. The Pankove Si-H-B model, therefore, remains intact.
INTRODUCTION The disruption of a crystalline solid by the presence of impurities has, for decades, presented scientists with an opportunity to probe the physics of many body atomic systems. Occasionally, rather basic principles have been distilled from observations and interpretations of such systems. We believe that the work described here can be considered as such an example. It has to do with an "anomalous" isotope shift reported recently [1i for a localized vibrational mode of deuterium in the deuterium-boron pair defect in silicon. As originally interpreted, the results served to challenge the generally accepted Pankove model [21 for the defect. In this paper, we conclude instead that the unexpectedly large isotope effect can be explained simply as arising from a small anharmonic coupling between the vibration of the deuterium atom and the nearly degenerate second harmonic of a perpendicular boron vibration. Classically, this corresponds to the parametric oscillator problem, or that of a child pumping a swing. Quantum mechanically, this is known as a Fermi resonance [3], a phenomenon well established for molecules [4] but not previously identified, we believe, for a defect in a solid. This interpretation, and the experimental confirmation that we present here, explains the isotope effect quite naturally in terms of the accepted model of the defect and, in fact, actually further strengthens it by confirming essential features not previously established.
THE PANKOVE MODEL The generally accepted model of the H-B pair, first presented by Pankove [2], has an interstitial hydrogen atom occupying a bond centered (BC) site directly between substitutional boron and one of its neighboring silicon atoms. In this model, as shown in Fig.
Data Loading...
