G. Tränkle

Size-induced direct-to-indirect gap transition in GaSb/AlSb multiple quantum well structures

Using excitation spectroscopy we have investigated the size-induced cross-over from direct to indirect bandstructure in GaSb/AlSb quantum wells. In samples with Lz < 30 A we observe in particular the emission from the indirect and the direct energy gap of the wells, whereas for larger Lz only the direct transition occurs. Time-resolved measurements yield a change of the carrier lifetime by about a factor of 100 at the cross-over.

Direct-indirect band gap crossover in two-dimensional GaSb/AlSb-quantum-well-structures

Abstract Using excitation and time-resolved spectroscopy we have investigated the size-dependent change from direct to indirect band structure in two-dimensional GaSb/AlSb structures. In the indirect regime (L z ⩽38 A) we observe L- and Λ-point transitions, whereas in the direct-gap samples only the Λ-point emission occurs. Direct evidence for the crossover is provided by the increase of the carrier life-time from less than 1 ns in direct-gap samples to more than 100 ns in indirect-gap samples.

Optical investigation of 2D Mott transitions in GaAs/GaAlAs quantum well structures

Abstract In transmission experiments performed under quasi-equilibrium conditions at low temperatures we investigated the bleaching of the quasi-2D excitons in GaAs/GaAlAs MQW structures with special emphasis on the behaviour of the excitons at the different subband edges. The 1hh excitons are found to be much more sensitive to bleaching than the other excitons. We attribute this to phase space filling effects which should reduce the 1hh excitonic structures additionally to the usual screening due to the long-range Coulomb interaction, which screens the excitons related to transitions between higher subbands only. We determined the 2D Mott density of the 2hh exciton performing a lineshape analysis of the luminescence of the electron-hole pairs measured simultaneously.

Verification of Direct-Indirect Cross-Over in GaSb/AlSb MQW's by Time Resolved Spectroscopy

In GaSb/AlSb multi quantum well structures (MQW) we previously observed a quantum size induced direct to indirect band structure transition at well widths around 40 A. Using time resolved optical spectroscopy, we investigated the time dependence of the quantum well emission as a function of the well width. The life time of the quantum well emission changes by two orders of magnitude if the well width of 40 A is exceeded. This verifies the direct to indirect cross-over in the GaSb/AlSb system

Optical spectroscopy on Eo+Δo transitions in GaSbAlSb quantum wells

Abstract We have investigated optical transitions between the lowest conduction subband (Γ6) and the split-off valence band (Γ7) in GaSb AlSb multi quantum wells with well widths between 40A and 120A. The corresponding emission lines at an energy Eo + Δ0 were observed in all samples and can be clearly associated with this transition by the variation with well width LZ. Temperature dependent investigations show a cross-over of the Δo and Eo energies in a temperature range between 280K and 700K which is strongly dependent on the well widths.

Quasi-two-dimensional electron-hole plasma in GaAs-GaAlAs MQW structures: Band-filling effects and band-gap renormalization

Abstract We investigated the photoluminescence of the electron-hole plasma in quasi-two-dimensional GaAs-GaAlAs multiple quantum well structures. Compared to the case of a three-dimensional plasma particularly strong band filling and large band-gap renormalization are observed. The dependence of the band filling and band-gap renormalization on the plasma density can be described quantitatively assuming recombination between electron and hole subbands including forbidden but parity-allowed transitions.

Spectroscopic investigation of electron-hole plasma properties in InGaAs/InP quantum well structures

Abstract Using photoluminescence we investigated the properties of quasi-two-dimensional electron-hole plasmas in lattice-matched InGaAs/InP-multi-quantum well structures under quasi-stationary excitation. From the lineshape analysis of the spectra we obtained the plasma parameters and information on the subband structure. From optical transitions between higher subbands we determine the conduction band discontinuity to be 210meV, corresponding to 35% of the total discontinuity.