Excitation Spectrum of Aluminum Acceptors in Diamond under Uniaxial Stress

A high-resolution survey of the 0.30-0.37-eV spectra, attributed to transitions at acceptor centers, obtained from several natural $p$-type semiconducting diamonds at 80°K, is presented. Effects on the spectrum of destruction of the normal site symmetry ($T_d$) by uniaxial compression are described. Hydrostatic stress has also been applied. Large spectral changes produced by uniaxial stress in the range 0-30 kbar have been analyzed in terms of the effective-mass theory of weakly bound electronic states, the lowest transitions being between quasihydrogenic $s-p$-like states. A coupling scheme here introduced for the $p$-like states is the opposite to that obtained for Si and Ge. Assignment of transitions has been made using theoretical band structures, results of reported spectral changes between 80 and 5°K, and the present stress spectra. Analysis of stress effects has been made using deformation-potential theory. The resulting potentials of ${D_u}^v=+2.47\mathrm{}$, ${D_u}^v=+1.63\mathrm{}$ eV are of the same sign as and similar magnitude to those of silicon.