Uniaxial-stress investigation of the phonon-assisted recombination mechanisms associated with the X states in type-II GaAs/AlAs superlattices

We present the results of a uniaxial-stress investigation of type-II GaAs/AlAs short period superlattices, using the optical techniques of photoluminescence (PL) spectroscopy and resonant Raman scattering. At ambient pressure, a resonance in the Raman cross section at the indirect, type-II band gap allows a direct measurement of the energies of the superlattice LA, GaAs-like LO, and AlAs-like LO phonons derived from the bulk X point. The positions of the Raman peaks are compared with the phonon-assisted PL transitions, indicating that the participation of GaAs-like LO phonons in the recombination process is not as well understood as has previously been thought. At sufficiently high in-plane stress, the transverse X minima become the conduction-band ground state, and the Raman measurements have again been used to examine the phonon modes, which can couple to these states. These measurements not only resolve an existing controversy in the literature, but they also demonstrate that one of the currently accepted assignments is incorrect.