Electron-optical phonon interaction and in-plane mobility in lead chalcogenide quantum-well structures

The in-plane electron mobility limited by scattering from optical phonons in lead chalcogenide (PbSnTe-type) quantum-well structures is studied theoretically. It is found that the mobility decreases drastically for quantum-well widths smaller than about 200 Å. The scattering from the interface phonons is responsible for that. The nonparabolicity considerably reduces the mobility. Influence of the nonparabolicity on the mobility essentially depends upon the growth axis of the quantum-well structure. It is found that the nonparabolicity in quantum-well systems can be successfully represented by two following effects: (1) dependence of the in-plane electron effective mass upon the in-plane electron wave vector (subband nonparabolicity), and (2) dependence of the in-plane electron effective mass upon the subband number and quantum-well width (in-plane mass quantization). It is shown that, if the quantum-well width exceeds 250 Å, influence of the nonparabolicity on the mobility is actually represented by the subband nonparabolicity alone, otherwise the in-plane mass quantization effect arises. The mobility of a many-subband system is found to be limited mainly by the intrasubband scattering. The mobility of electrons in a higher subband is smaller than that in the first one, which is due to the larger in-plane effective mass and stronger scattering rates in the higher subband. The mobility is essentially affected by electrons in a higher subband, while the gap between this subband and the ground one does not exceed $k_{B}T$. The electrophonon resonance effect is also considered.