Electronic Raman and infrared spectra of acceptors in isotopically controlled diamonds

Abstract

The Lyman spectrum of substitutional boron acceptors in diamonds with natural composition and that in a ${}^{13}\mathrm{C}$ diamond exhibit remarkably similar features, but shifted to higher energies in the latter by 0.4--1.5 meV. Additional lines appear when the spectra are recorded as a function of temperature, indicating the thermal population of a level ${\ensuremath{\Delta}}^{\ensuremath{'}}\ensuremath{\sim}2\mathrm{meV}$ above the ground state; this can be interpreted as the spin-orbit splitting of the $1s$ acceptor ground state into ${1s(p}_{3/2})$ and ${1s(p}_{1/2}),$ the latter located ${\ensuremath{\Delta}}^{\ensuremath{'}}$ above the former. The Raman-allowed ${1s(p}_{3/2})\ensuremath{\rightarrow}{1s(p}_{1/2})$ electronic transition is directly observed at 2.07(1) and 2.01(1) meV in the Raman spectrum of natural and ${}^{13}\mathrm{C}$ diamond, respectively. Polarization features of the ${\ensuremath{\Delta}}^{\ensuremath{'}}$ Raman line reveal that it is predominantly ${\ensuremath{\Gamma}}_{5}$ in character, as predicted by a theoretical calculation formulated in terms of the known values of Luttinger parameters. The theoretical expression for the Raman cross section for ${\ensuremath{\Delta}}^{\ensuremath{'}}$ enables the acceptor concentration to be deduced from an intercomparison of the intensity of the ${\ensuremath{\Delta}}^{\ensuremath{'}}$ line and that of the zone-center optical phonon. The presence of boron acceptors produces a quasicontinuous absorption spectrum in the range of the optical phonon branch, flanked by a sharp feature at the zone-center optical phonon frequency; their appearance can be attributed to the partial breakdown of the translational symmetry and the activation of otherwise inactive vibrations.