Piezospectroscopic study of the Raman spectrum of cadmium sulfide

The effect of uniaxial stress on the one-phonon Raman lines of CdS having $A_1$, $E_1$, and $E_2$ symmetries are studied for compressive force $\overrightarrow{\mathrm{F}}$, either along the $a$ axis ($\hat{x}$) or the $c$ axis ($\hat{z}$) and using a low-temperature stress cryostat. The scattering geometries chosen resulted in the phonon propagation direction $\overrightarrow{\mathrm{q}}$ being either parallel or perpendicular to $z$; this in turn allowed the observation of pure $E_1\left(\mathrm{TO}\right)$, $E_1\left(\mathrm{LO}\right)$, $A_1\left(\mathrm{TO}\right)$, and $A_1\left(\mathrm{LO}\right)$ lines. For $\overrightarrow{\mathrm{F}}\parallel \hat{x}$, the lines or their components shift linearly with stress. The $E_2$ line at 256 ${\mathrm{cm}}^{-1\mathrm{}}$ splits into two clearly resolved components, the polarization features being consistent with the deformation-potential theory. The $E_1\left(\mathrm{TO}\right)$ and the $E_1\left(\mathrm{LO}\right)$ lines separate further, whereas the $A_1\left(\mathrm{TO}\right)$ and the $A_1\left(\mathrm{LO}\right)$ lines increase at the same rate. For $\overrightarrow{\mathrm{F}}\parallel \hat{z}$, all the lines exhibit shifts linear in stress; the $E_1\left(\mathrm{TO}\right)$ and the $E_1\left(\mathrm{LO}\right)$ lines increase at the same rate, and the $E_2$ line at 256 ${\mathrm{cm}}^{-1\mathrm{}}$ does not split. From the results for $\overrightarrow{\mathrm{F}}\parallel \hat{x}$ and $\overrightarrow{\mathrm{F}}\parallel \hat{z}$, the deformation-potential constants characterizing each line have been deduced. A comparison of the piezospectroscopy of the doubly degenerate $E_1$ line of CdS with that of the $E$ lines of $\alpha$-quartz is presented along with some new results for the latter. The LO overtones observed in $\overline{\mathrm{y}}\mathrm{}\left(\mathrm{zz}\right)y$ geometry shift linearly for $\overrightarrow{\mathrm{F}}\parallel \hat{z}$, the rates of shift increase linearly with increasing order. The magnitudes of these shifts suggest that all overtones are of $E_1$ nature.