U. Cebulla

Well width dependence of the carrier life time in InGaAs/InP quantum wells

Abstract Investigations of the well width dependence of the radiative excitonic life time of InGaAs/InP quantum wells are reported, for well widths between 1 nm and 50 nm. The luminescence of the 1-1 transition of the quantum wells is detected via time resolved frequency up-conversion with the exciting Nd-YAG laser. In our experiments the time constants reveal an interesting phenomena with respect to the potential well thickness. For decreasing well widths we observe decreasing time constants of the excitonic recombination as has been observed for several other quantum well systems. But for well thicknesses below approximately 5 nm we find an increase of the life time with further decrease of the well widths. We explain the increase for small well widths by the reduced transition probability due to the delocalization of the envelope wavefunction of the electron in very small quantum wells.

Electron capture processes in optically excited In0.53Ga0.47As/InP quantum wells

We have performed picosecond time‐resolved measurements on In0.53Ga0.47As/InP quantum wells with varying barrier thicknesses using 10 ps Nd:YAG excitation. For this excitation, holes and electrons are created in the In0.53Ga0.47As layers. Due to momentum conservation the Nd:YAG excitation accelerates the electrons above the InP barrier where they can diffuse but cannot recombine. By examining the rise time of the quantum well emission, we can show that for samples with thick barriers, the barrier geometry largely controls the dynamic properties of the carriers after Nd:YAG excitation.

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 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.

Barrier controlled hot carrier cooling in In0.53Ga0.47As/InP quantum wells

Abstract We have investigated the influence of the barrier thickness on hot carrier cooling in In0.53Ga0.47As/InP quantum wells by picosecond time resolved spectroscopy. Striking differences of the cooling of hot electrons and holes are observed for different barrier thicknesses. For small barrier thicknesses the initial carrier temperatures are significantly higher than for large barrier thicknesses. We can explain this behaviour by microscopic calculations of the transient variation of the carrier densities and the thermalization of hot carriers in the quantum well.

Optical Spectroscopy on Two- and One-Dimensional Semiconductor Structures

Due to the enormous progress of epitaxial techniques many semiconductor materials can nowadays be fabricated with a previously unattained degree of perfection. In particular molecular beam epitaxy (MBE) and metalorganic vapour phase epitaxy (MOVPE) have been developed during the last decade.1,2 They allow the growth of high quality sequences of III-V-semiconductor materials. With these methods the growth can be controlled down to the level of individual atomic layers.3

Hot carrier relaxation and recombination in GaSb/AlSb quantum wells

Abstract We present picosecond time-resolved experiments on GaSb/AlSb quantum wells using a sum frequency generation technique. Recombination processes as well as relaxation and cooling processes of hot carriers in 2D GaSb/AlSb systems are studied. As a result, we find LO-phonon scattering times τ LO of about 12ps.