Observation of higher confined exciton states in serpentine superlattices by linear polarized excitation spectroscopy

Abstract
(Al,Ga)As serpentine superlattice (SSL) quantum-wire arrays with a paraboliccrescent cross section have been grown on vicinal GaAs substrates by molecular beam epitaxy. The quantum wires have dimensions on the order of 5 nm and 1D confined valence band states have been reported previously. Here we report on subsequent SSL samples having photoluminescence (PL) linewidths of 5 meV and displaying well-resolved excitation spectra. The data were obtained at 1.4 K and include linearly-polarized PL and PL excitation spectra (PLE) taken normal to the vicinal (100) surface. These data were fitted with effective-mass calculations that include the SSL geometry, valence band mixing, and imperfect lateral composition modulation. In linear polarized PLE (polarized parallel and perpendicular to the quantum wires), we have been able to resolve a SSL-induced heavy-light hole splitting of the ground state exciton. The observed heavy-light hole splitting is of the order of 5 meV with an electron-heavy hole subband separation of 15-20 meV. We extract a lateral composition modulation between the barrier and the wire to be 15 % from the observed heavy-light hole splitting corresponding to a lateral potential-energy difference in the conduction band of about 120 meV.