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Abstract

We report the first high resolution photoluminescence studies
of isotopically pure silicon. New information is obtained on
isotopic effects on the indirect band gap energy, phonon
energies, and phonon broadenings, which is in good agreement
with previous results obtained in germanium and diamond.
Remarkably, the line widths of the no-phonon boron and
phosphorus bound exciton transitions in the Si-28 sample
(99.896% Si-28) are much sharper than in natural Si, revealing
new fine structure in the boron bound exciton luminescence.
Most surprisingly, the small splittings of the neutral acceptor
ground state in natural Si are absent in the photoluminescence
spectra of acceptor bound excitons in isotopically purified Si-
28, demonstrating conclusively that they result from the
randomness of the Si isotopic composition.