Effect of Pressure on Interband Reflectivity Spectra of Germanium and Related Semiconductors

The pressure dependences of the position of peaks occurring between 2 and 5 eV in the reflectivity spectra of Ge, Si, GaSb, InSb, InAs, and GaP have been measured to 10 kbar, and the results taken to give the pressure coefficient of energy separations corresponding to direct interband transitions. Seven peaks between 2 and 3 eV, members of $E_1$, $E_1+{\Delta }_1$ doublets associated with ${{\Lambda }_3}^v\to {{\Lambda }_1}^c$ transitions, shift to higher energy at rates between +6×$0^{-6\mathrm{}}$ and +9×${10}^{-6\mathrm{}}$ eV/bar. No pressure dependence of ${\Delta }_1$, the spin-orbit splitting of the ${{\Lambda }_3}^v$ valence band, was found within the experimental accuracy of ±1×${10}^{-6\mathrm{}}$ eV/bar. The dominant $E_2$ peak near 4 eV has a pressure coefficient of about +6×${10}^{-6\mathrm{}}$ eV/bar for Ge, GaSb, and InSb, and +3×${10}^{-6\mathrm{}}$ eV/bar for Si. The peaks at 3.4 eV in Si and 3.7 eV in GaP possess coefficients of +5×${10}^{-6\mathrm{}}$ and +6×${10}^{-6\mathrm{}}$ eV/bar, respectively. The addition of these data to earlier results on the pressure dependences of energy separations in this family of semiconductors modifies and extends a previously noted correlation between transition type and pressure coefficient. A comparison of the measured coefficients with recently reported calculations reveals considerable agreement, with the discrepancies suggesting that a reinterpretation is required for the $E_2$ peaks and, especially, for the peak at 3.4 eV in Si.