G. Griffiths

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.

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

Recombination in GaSbAlSb multiple QWS under high excitation conditions

Abstract We have studied the recombination dynamics in GaSb AlSb MQW structures under high excitation conditions. Time-resolved measurements were performed using the up-conversion technique. The carrier dynamics in these structures is strongly influenced by the small energetic separation between the Γ-valley and the L-valleys even in the direct material with Lz ≥ 40 A. At room-temperature we find that the Auger recombination with its coefficient C = 4 · 10−28cm6s−1 is the dominant recombination mechanism at high carrier densities. The Auger coefficient C shows a monotonic increase with temperature up to 400 K in contrast to theory.

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.

E0+Δ0 transitions in GaSb/AlSb quantum wells

We have observed optical transitions between the first subbands of the conduction band and the split‐off valence band in GaSb/AlSb quantum well structures. The well width dependence of the emission energies is traced to quantization in the conduction band and in the split‐off band. By comparison with data for the band‐edge transitions the effective Δ0 gaps is the quantum wells are determined. Contrary to previous calculations the Δ0 gap energies are almost independent of the well width.

Auger recombination in GaSbAlSb multi quantum well heterostructures

The experimental determination of Auger coefficients in GaSbAlSb multi quantum well heterostructures is reported for the first time. The luminescence at Eg and Eg+Δ0, recorded under the same experimental conditions, is used to monitor the carrier recombination channels. A quantitative determination of the recombination coefficients is achieved applying coupled carrier rate equations for the conduction and the valence subbands including the split-off valence band. Information on the actual carrier density is obtained by line shape analysis of the Eg-emission. Two dimensional carrier densities up to 1012cm−2 are determined. Auger coefficients exhibit a pronounced well width dependence: above 100A C ∼- 4·10−27s−1cm6 whereas at 50A values are 10 times smaller. No resonance of the Auger recombination is observed tuning the band gap energy over the spin-orbit splitting with temperature.