The pressure dependence of the direct and indirect bandgap of epitaxial In_0.52Al_0.48As on InP(001) substrate has been measured using photoluminescence up to 92 kbar hydrostatic pressure. The bandgap changes from Γ toX at an applied pressure of ∼ 43 kbar. Hydrostatic deformation potentials for both the Γ andX bandgaps are deduced, after correcting for the elastic constant (bulk modulus) mismatch between the epilayer and the substrate. For the epilayer we obtain$$(\Xi _d + \tfrac{1}{3}\Xi _u - a) as - (6 \cdot 92 + 0 \cdot 3) eV$$ and+(2.81±0.15)eV for the Γ andX bandgaps respectively. From the pressure dependence of the normalized Γ-bandgap photoluminescence intensity a Γ-X lifetime ratio, (τ_Γ/τ_X), of 4.1×10⁻³ is deduced.

Hydrostatic pressure has been used to tune in resonance Raman scattering (RRS) in bulk GaAs. Using a diamond anvil cell, both the photoluminescence peak (PL) and the 2 LO and LO-phonon Raman scattered intensities have been monitored, to establish RRS conditions. When theE₀ gap of GaAs matchesħω_S orħω_L, the 2 LO and LO-phonon intensity, respectively, exhibit resonance Raman scattering maxima, at pressures determined byħω_L. With 647.1 nm radiation (ħω_L = 1.916 eV), a sharp and narrow resonance peak at 3.75 GPa is observed for the 2 LO-phonon. At this pressure the 2 LO-phonon goes through its maximum intensity, and falls right on top of the PL peak, revealing thatħω_S(2 LO) =E₀. This is the condition for “outgoing” resonance. Experiments with other excitation energies (ħω_L) show, that the 2 LO resonance peak-pressure moves to higher pressure with increasingħω_L, and the shift follows precisely theE₀ gap. Thus, the 2 LO RRS is an excellent probe to follow theE₀ gap, far beyond the Γ-X cross-over point. A brief discussion of the theoretical expression for resonance Raman cross section is given, and from this the possibility of a double resonance condition for the observed 2 LO resonance is suggested. The LO-phonon resonance occurs at a pressure whenħω_L ≈E₀, but the pressure-induced transparency of the GaAs masks the true resonance profile.