Confined and Interface Phonons in Chirped GaAs-AlGaAs Superlattices

The confined longitudinal optical, transverse optical and interface phonon modes in chirped GaAs-AlGaAs superlattices grown on the (001)-oriented GaAs substrate are studied by the micro-Raman spectroscopy. The phonon modes are probed at the (001) and (110) faces. The temperature dependence of the longitudinal optical, transverse optical and interface phonon modes are achieved. The temperature dependence of the longitudinal optical phonon frequencies demonstrates that a tensile strain exists in the GaAs layers of the chirped superlattices, which is significant for analyzing the device failure of a terahertz quantum cascade laser.