Frequency shifted polaron coupling in GaInAs heterostructures.

Frequency dependent cyclotron resonance measurements are reported on Ga(.47)In(.53)As-InP and Ga(.47)In(.53)As-Al(.48) In(.52)As heterostructures. Discontinuities in the effective mass are observed at two frequencies, due to resonant polaron coupling to the two optic phonon modes in GaInAs. In heterojunctions the coupling occurs at the frequencies of the TO phonons, in contrast to bulk materials, and the relative strength of the coupling to the two modes is different in the two systems. In more lightly doped superlattices the coupling is stronger, leading to larger shifts in the effective mass, and occurs at the LO phonon frequencies. This behaviour is discussed in terms of possible changes in the screening and polarization of the optic phonon modes.