No-phonon and phonon-assisted transitions in indirectGaAs1−xPxmodulation spectra

The fine structure of the intrinsic absorption edge of indirect $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloys has been investigated by piezomodulation spectroscopy, between 10 and 300°K. Both zero-phonon as well as momentum-conserving-phonon indirect transitions are very well resolved. According to the data obtained, the composition dependence of the indirect energy gap $E_g^x$ can be well represented by the usual parabolic equation. In agreement with the two-mode behavior of this alloy we obtain a constant value of the $\mathrm{LA}\mathrm{}\left(X\right)\mathrm{}$, $\mathrm{TA}\mathrm{}\left(X\right)\mathrm{}$, $\mathrm{LO}\mathrm{}\left(X\right)\mathrm{}$, $\mathrm{TO}\left(\Gamma \right)$, and $\mathrm{LO}\left(\Gamma \right)$ phonon energies.