P. Tronc

Stark localization in GaAsGaAlAs superlattices under a low electric field

Abstract We show, from the photoluminescence of a GaAsGa0.65Al0.35As superlattice of period 70 A, that the localization of the electrons takes place at low field (≈ 1 × 104 V cm−1). Before the localization, the energy of the photoluminescence line does not vary appreciably with the electric field. When the localization begins, the binding energy of the heavy-hole exciton is approximately the same whether the electron wave-function is centered on the same well as the hole or an adjacent well.

Optical properties and fluctuations of composition in Ga0.77In0.23As0.19Sb0.81 alloys

Low temperature (T < 10 K) photoluminescence experiments can be used to measure the bandgap fluctuations in a quaternary GaxIn1−xAsySb1−y alloy lattice-matched to GaSb. At x = 0.77 and y = 0.19, the bandgap variations of layers prepared by liquid phase epitaxy are fitted by a Gaussian distribution with a root mean square value of 4.2 meV. It is shown that the local fluctuations of composition and the correlative stress within the layer partially compensate to reduce the fluctuations of bandgap.

Excitonic transitions in GaAsGaAlAs superlattices under a weak electric field

Abstract We report a study of the photoluminescence spectra of GaAsGa0.65Al0.35As superlattice under an electric field of about 10 kVcm−1, from 9 K up to 80 K; the ratio ϱ = I −1 I 0 of the intensities of the −1 and 0 peaks of the Wannier-Stark ladder varies with the temperature T. To fit these variations, we assume for both transitions, a trapped exciton density of states with a gaussian distribution of eigenenergies, and a two dimensional density of states for free excitons. We show that above about 50 K there is a thermal equilibrium between direct and crossed free excitons whereas at low temperatures, the equilibrium statistics are not respected: the excitons trap into the direct state rather than to the crossed one.

Stark localization in GaAs-GaAlAs superlattices under a low electric field

Abstract We show, from the photoluminescence of a GaAs-Ga 0.65 Al 0.35 As superlattice of period 70 A, that the localization of the electrons takes place at low field (∼ 1 × 10 4 V/cm). When the localization begins, the binding energy of the heavy-hole exciton is approximately the same whether the electron wavefunction is centered on the same well as the hole or on adjacent well. The model of eigenfunctions proposed by Bleuse et al. for superlattices under electric field fits our results satisfactorily. A reduction of the electric field applied to the superlattice has been obtained by using a laser beam with photon energies greater than the bandgap width of the barriers. This effect provides accurate measurements of the low field localization.