Ultrahigh resolution photoluminescence spectroscopy of isotopically pure silicon

摘要

We report the first high resolution photoluminescence studies of isotopically purified Si. New information is obtained on the effects of isotopic composition on the indirect band gap energy, phonon energies, and phonon broadenings. Remarkably, the linewidths of the no-phonon bound exciton transitions in the ~(28)Si sample (99.896% ~(28)Si) are found to be much sharper than what has been previously observed in the best natural Si samples, revealing band gap fluctuations due to isotopic randomness to be the limiting factor on bound exciton linewidths in natural Si. Even more surprisingly, the small but reproducible splittings of the neutral acceptor ground state, which have been studied for many years using a wide variety of techniques in natural Si, are found to vanish in ~(28)Si. Thus this 'residual' acceptor ground state splitting is also found to result from the randomness of the isotopic composition in natural Si.