Inelastic phonon scattering in long-range-ordered (Al_0.5Ga_0.5)_0.5In_0.5P

Carrier relaxation and recombination in long-range-ordered (Al_0.5Ga_0.5)_0.5In_0.5P have been studied by selectively excited photoluminescence (PL) spectroscopy. We observed sharp resonant PL peaks under near-resonant excitation. The set of resonant PL peaks evolves according to excitation energy. The excess excitation energies for the resonant PL peaks agree well with the LO-phonon energies related to the In-P, Ga-P, and Al-P bonds of the ordered sample. Furthermore, the LA resonance caused by zone-folding effects was observed. These resonant PL intensities show different excitation energy dependence, which precludes the possibility of resonant Raman scattering. High dense excitation reveals an excited state near the X level. This suggests mixing of electron wave functions in the Γ and X states. Energy relaxation of excited carriers from the pseudodirect X state to the Γ ground state causes the resonant PL. Time-resolved spectroscopy was employed to study the carrier relaxation mechanism.