The coupling of intersubband transitions and the quantum-well LO phonon in p-doped GaAs-GaAlAs multiple-quantum wells

The authors have applied resonant Raman spectroscopy to two p-type modulation-doped GaAs-GaAlAs multiple-quantum wells (MQW) with well widths dW=10 and 30 nm. In both samples one of the hole intersubband transitions observed is coupling to the quantum-well LO (longitudinal optical) phonon. The influence of an external magnetic field on this coupling phenomenon was investigated. A shift of the intersubband transition energy with excitation energy due to well width fluctuations results in an anticrossing of the two branches of the coupled modes. From the strength of the coupling as well as from the small depolarization shift of the intersubband transitions, the conclusion must be drawn that depolarization field effects are of low importance in p-doped MQW structures. The coexistence of a non-interacting quantum-well LO phonon is discussed in detail