Ultrasonic Investigation of the Acceptor Ground State of Si(B) I. The Longitudinal and Transverse Relaxation Rates of the Strain‐Split Two‐Level System

Abstract

The "spin"-lattice relaxation of the two-level system of the strain-split acceptor ground state of Si(B) is determined from the temperature dependence of the ultrasonic relaxation attenuation, around 10 K. It is found that Raman relaxation alone does not fit the results but that, in addition, an Arrhenius-type of relaxation, possibly due to a Jahn-Teller effect, is involved. The transverse relaxation is obtained from intensity-dependent and hole-burning measurements of the resonant attenuation. At small acceptor concentrations it is determined by "spin"-lattice relaxation alone ; for higher concentrations an additional temperature-independent interaction term is found much smaller than expected for elastic dipole or exchange interaction.Die ,,Spin"-Gitter-Relaxation des Zweiniveausystems des Akzeptorgrundzustandes von Si(B) wird durch Messung der Ultraschallrelaxation im Bereich um 10 K untenucht. Ramanprozesse allein reichen zur Beschreibung der Resultate nicht Bus. Es ist noch eine Arrhenius-Relaxation beteiligt, die wir dem Jahn-Teller-Effekt zuschreiben. Die transversale Relaxation wird aus intensitatsabhangigen und hole-burning-Meseungen der Resonanzdimpfung bestimmt. Bei kleinen Azeptorkonzentrationen ist die ,,Spin"-Gitter-Relaxation allein mal3gebend; bei hoheren Konzentrationen kommt ein temperaturunabhingiger Wechselwirkungsterm hinzu, der aber kleiner ist, als es fur elastische Dipol-oder Austauschwechselwirkung erwartet wird.

Photoluminescence studies of isotopically enriched silicon

“…While phonon assisted transitions are broadened through the wave-vector conserving phonons, these PL transitions are very sharp in natural Si and can only be resolved by Fourier transform spectroscopy [44]. Our investigations in isotopically purified 28 Si (SI283, enriched to 99.896% 28 Si) revealed that these transitions become even sharper in this material. We start our discussion with the P donor and B acceptor BE transitions in isotopically enriched 28 Si.…”

“…The natural Si sample used for comparison was a float-zone crystal selected to have approximately the same B and phosphorus (P) concentration as the 28 Si sample, which was cut from the SI283 crystal. This crystal was used previously for thermal conductivity studies and Hall measurements [19,20,41].…”

“…Remarkably, the line widths of the no-phonon boron and phosphorus bound exciton transitions in the 28 Si sample (99:896% 28 Si) 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 28 Si, demonstrating conclusively that they result from the randomness of the Si isotopic composition. …”

“…Remarkably, the no-phonon bound exciton (BE) PL lines, which have already been shown to be extremely sharp in natural Si, are much narrower in the 28 Si sample. Thus, the limiting broadening mechanism for the no-phonon BE PL in high purity Si is found to result from the isotopic randomness.…”

“…Previous studies on isotopic effects in silicon (Si) have been limited to Raman scattering [17,18], thermal conductivity [19,20], and the direct gap due to a lack of bulk samples of sufficient purity for a study of the indirect band gap via photoluminescence (PL) until the recent growth of the samples for the aforementioned thermal conductivity studies. In this article, we report on the differences between the PL spectra of natural Si (92:23% 28 Si þ 4:67% 29 Si þ 3:10% 30 Si) and isotopically enriched 28 Si, 29 Si, and 30 Si, obtaining new experimental data on the isotope effect on the indirect band gap of Si, together with new information on changes in phonon energies and lifetimes [21].…”