MAGNETIC-FIELD-ENHANCED RAMAN-SCATTERING BY INTERFACE PHONONS IN P-TYPE MODULATION-DOPED MULTIPLE-QUANTUM WELLS

We have investigated the coupling of hole intersubband transitions and phonons in p-type modulation-doped GaAs-AlxGa1-xAs multiple quantum wells by means of resonance Raman spectroscopy. Magnetic fields with flux densities up to B = 14 T were applied, oriented parallel to the growth direction. For B = 0 T the spectra can be interpreted in terms of a Fano interference of the zone-centre quantum well LO phonon with a quasi-continuum of hole transitions between the lowest and the second excited heavy-hole subband. For B > 4 T we observe the coupling of a hole intersubband transition with interface phonons. The character of the latter modes is deduced from a comparison of the excitation energies with values calculated within a dielectric continuum model as well as from their behaviour under photoexcitation. Our measurements indicate an interaction of the Frohlich type, where the strength of the coupling seems to increase with the in-plane wavevector of the excitations. The ionized impurities in the barriers dominate the relaxation of wavevector conservation in the scattering process.