Pressure-tuned resonance Raman scattering in Ga^1-x-In^xAs/Ga^1-yA1^yAs strained layer multiple quatum well structures

Abstract

Pressure-tuned Resonance Raman Scattering (RRS) experiments in Ga_1-xIn_xAs/Ga_1-yAl₃ As strained layer quantum-well samples with x = 00.15 and y=0.15, 0.30 and 0.45 A, B and C respectively on GaAs substrate, are reported. The photoluminescence (PL), the 2LO and the LO-phonon Raman scattered intensities were followed as a function of pressure using the diamond cell. Depending on the composition and excitation energy, sharply defined 2LO-phonon resonance profiles (Raman Intensity vs. pressure) are observed. These are identified to be from the AIGaAs, GaAs and InGaAs, layers with increasing pressure. AI the peak of resonance, the 2LO of the layer falls right on top of the PL peak of the corresponding layer, revealing that the resonance occurs when E₀= hw_s(2LO). The LO-resonance profile (pressure vs. phonon intensity) is narrow only for the AIGaAs, and is broad and asymmetric in the case of GaAs. The LO-resonance from the InGaAs layer is totally masked by the strong GaAs-LO-phonon. From the PL data and the incident and scattered photon energies, we present a key-diagram to predict pressure-induced RRS in zinc-blende semiconductors at their E₀ gaps. A brief discussion of the theory of RRS cross section is given, and it is suggested that the observed 2LO-resonance scattering is dominated by Frölich interaction, and that it could be a double resonance. Pressure-induced transparency, is a serious problem when dealing with pressure tuned RRS. in MQW structure with GaAs or AlGaAs substrates. The usefulness of the 2 LO-resonance in locating the En gap and to characterize MQW layers is indicated.