Quantum-well structures of direct-band-gap ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$/GaAs studied by photoluminescence and Raman spectroscopy

We report the successful growth of quantum-well structures of ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$/GaAs/${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ on GaAs substrates. The samples are studied by photoluminescence and Raman spectroscopy. The structures are grown by metalorganic vapor-phase epitaxy with the thin ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ barriers strained to the GaAs crystal lattice. Quantum size effects are observed in the structures as optical transitions in photoluminescence and photoluminescence-excitation spectroscopy. The strain in the pseudomorphic ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ barriers is studied by Raman spectroscopy through the investigation of strain-induced frequency shifts of the LO phonons. By using thick, relaxed ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ alloy samples as references, the compositions x in the thin, strained ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ barriers can be determined from the ratio of the intensity of ${\mathrm{LO}}_{\mathrm{GaP}}^{\mathrm{\Gamma }}$ to that of ${\mathrm{LO}}_{\mathrm{GaAs}}^{\mathrm{\Gamma }}$. The strain-induced Raman-frequency shift has been obtained by subtracting the alloy-induced shift from the total measured frequency shift. Our results are in reasonable agreement with lattice-dynamic theory.