Comparative study of phonon modes in ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{P}$ and $\mathrm{Ga}{\mathrm{As}}_x{\mathrm{P}}_{1-x}$ alloys

The "one-mode" and "two-mode" behaviors of ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{P}$ and $\mathrm{Ga}{\mathrm{As}}_x{\mathrm{P}}_{1-x}$ alloys have been studied as a function of the concentration $x$ and the hydrostatic pressure by means of Raman spectroscopy. A detailed comparative study of the experimental results shows that the concept of a one-mode system is not appropriate to describe the physics of this kind of alloy. A more realistic picture should involve a selective activation of the alloy phonon density of states for each observed structure.