Raman and modulated-reflectivity spectra of a strained pseudomorphic ZnTe epilayer on InAs under pressure

The piezomodulated-, electromodulated-, and photomodulated-reflectivity spectra of a pseudomorphic ZnTe epilayer, grown on an InAs epilayer by molecular-beam epitaxy, exhibit heavy- and light-hole excitonic signatures split by the lattice mismatch induced biaxial compressive strain. This splitting in the pseudomorphic epilayer is studied as a function of applied hydrostatic pressure using photomodulated reflectance spectroscopy at 80 K. With increasing hydrostatic compression, the compressive strain is progressively compensated by the pressure-induced tensile strain. At ∼55 kbars the epilayer becomes strain-free, and is under a biaxial tension at higher pressures. The separation between the heavy- and light-hole signatures is superlinear in pressure, suggestive of a strain or volume deformation-dependent shear deformation-potential constant. We also compare the pressure dependence of the Raman LO phonon of the ZnTe epilayer on InAs with that of a bulk ZnTe sample at 13 K. The pressure-dependent strain is found to be linear. Accurate values of the first-order strain derivatives of the LO phonons and mode Grüneisen constants are obtained.