[en] Elastically strain-relaxed GaAs/In_0.08Ga_0.92As/GaAs heterostructures on GaAs (0 0 1) substrates were fabricated by the in-place bonding method. Pseudomorphic heterostructures were patterned and an underlying sacrificial AlAs layer was removed by selective etching. As the GaAs/InGaAs/GaAs structure is released from the substrate, elastic strain relaxation occurs in agreement with a force-balance model and the strain-relaxed structures are weakly bonded in place to the substrate. The bond between the strain-relaxed structure and the substrate was subsequently strengthened by annealing at 400 °C. The increase in the in-plane lattice parameter of these bonded GaAs/In_0.08Ga_0.92As/GaAs structures is 0.25–0.37%

[en] A power-dependent relative photoluminescence measurement method is developed for double-heterostructures composed of III-V semiconductors. Analyzing the data yields insight into the radiative efficiency of the absorbing layer as a function of laser intensity. Four GaAs samples of different thicknesses are characterized, and the measured data are corrected for dependencies of carrier concentration and photon recycling. This correction procedure is described and discussed in detail in order to determine the material's Shockley-Read-Hall lifetime as a function of excitation intensity. The procedure assumes 100% internal radiative efficiency under the highest injection conditions, and we show this leads to less than 0.5% uncertainty. The resulting GaAs material demonstrates a 5.7 ± 0.5 ns nonradiative lifetime across all samples of similar doping (2–3 × 10"1"7" cm"−"3) for an injected excess carrier concentration below 4 × 10"1"2" cm"−"3. This increases considerably up to longer than 1 μs under high injection levels due to a trap saturation effect. The method is also shown to give insight into bulk and interface recombination.

[en] Engineered or ‘virtual’ substrates are of interest to extend the range of epitaxially-grown semiconductor heterostructures available for device applications. To this end, elastically strain-relaxed square features up to 30 µm in size and having an in-plane lattice constant as much as 0.49% larger than the lattice constant of GaAs were fabricated from MOCVD-grown GaAs/In_0.08Ga_0.92As/GaAs heterostructures by the in-place bonding method, using either AlAs or Al_0.7Ga_0.3As as the sacrificial layer. TEM images show that the solution-bonded interface is flat with a network of sessile edge dislocations that accommodates the different in-plane lattice constants of the feature and the GaAs substrate and a small rotation of the bonded features. Micro-Raman spectroscopy, which has a spatial resolution of ∼1 µm, was shown to be useful for characterizing lattice mismatch strain ≥ 0.0023, i.e. with an order of magnitude lower sensitivity than high-resolution XRD. (paper)

[en] Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.