The carrier localization phenomenon has been investigated for GaBiAs by photomodulated transmittance (PT) and photoluminescence (PL). In the case of PT measurements, a decrease in the energy-gap related PT signal has been clearly observed below 180 K. In PL spectra a broad emission band very sensitive to the excitation power has been found. In comparison to the energy-gap related transition, this band is shifted to red. The recombination time for this band at low temperature decreases from 0.7 to 0.35 ns with the increase in the emission energy. All the findings are clear evidences for strong carrier localization in this alloy.

In x Ga 1 − x As ∕ Ga As quantum dots (QDs) were grown by solid source molecular beam epitaxy for indium contents of around 30%, which assures the QD growth in the very low strain limit. The structures were fabricated for a constant nominal InxGa1−xAs layer thickness but varying content (strain) from below to far above the critical thickness conditions, which has allowed to detect the onset of three-dimensional island formation and their evolution with the increasing material amount (for higher In contents the critical thickness for island formation is smaller and hence a larger fraction of the InxGa1−xAs layer is spent on dot formation). In order to investigate the properties of such an uncommon QD system, photoreflectance and photoluminescence, combined with scanning electron microscopy, have been used. Optical transitions connected with the ternary layer have been observed and followed from the lowest content quantum well case through the transformation into three-dimensional islands on the wetting layer (WL) and a coexistence of the QD-related and WL-related transitions. Due to the observation of both heavy hole and light hole related transitions in photoreflectance spectra, the thickness of the wetting layer versus changed indium content could be determined, comparing the experimental data with the results of the effective mass envelope function calculations.

Here comes a report on the investigation of the energy transfer in InP-based tunnel injection structures, consisting of InAs∕InAlGaAs quantum dashes (QDashes) and an InGaAs∕InAlGaAs quantum well (QW), designed for 1.55μm emission at room temperature. Temperature dependent photoluminescence excitation (PLE) spectroscopy was used to experimentally confirm that the carriers created in the well reach the quantum dash layer by the tunneling through a thin InAlAs∕InAlGaAs barrier and recombine there radiatively. A measurable QW-QDash energy transfer has been detected up to 130K. The electronic structure of the whole complex system obtained by modulation spectroscopy exhibits full conformity with the PLE measurement results.