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InGaAs/GaAs-based lasers require thick AlGaAs cladding layers to provide optical confinement. Although the lattice mismatch between GaAs and AlGaAs is very low, relaxation may occur due to the thickness requirement for an AlGaAs waveguide of the order of microns. We have studied the relaxation of InGaAs/GaAs lasers with AlGaAs waveguides grown on GaAs (111)B substrates. We have observed by transmission electron microscopy (TEM) that certain AlGaAs layers show a high density of threading dislocations (TDs), whilst other AlGaAs layers remain essentially dislocation free. To explain the experimental results a model based on dislocation multiplication has been developed. TDs in the AlGaAs cladding layers are observed when the critical layer thickness (CLT) for dislocation multiplication has been overcome. Consequently, a design rule based on a modified CLT model for AlGaAs/GaAs (111)B is proposed.

The plastic relaxation of InGaAs/GaAs(111)B quantum wells (QWs) is investigated. Critical layer thickness (CLT) models based on the theory of Matthews–Blakeslee have been applied, assuming that dislocations glide from the substrate. We have observed that when the In-content is above 0.25, a three-pointed star-shaped misfit dislocation (MD) configuration appears. A detailed analysis has shown that this configuration cannot originate from the glide of pre-existing dislocations. Instead, these MDs are generated by climb from an initial nucleus. A modified Matthews–Blakeslee model including an osmotic force component is proposed. The resulting revised CLT depends on the departure of the vacancy concentration from its equilibrium.

A study of the optical and electrical activity of defects at the surface of InGaAs/GaAs multiple quantum well pin photodiodes was done on two different misoriented (111)B GaAs substrates: substrate A, misoriented 1° towards [211] and substrate B, misoriented 2° towards [211]. In this article, we report the existence of different faceted defects at the surface with the misorientation and their influence on the optical performance. The surface of photodiodes grown on substrate A shows inclined pyramids with two enhanced facets. The electron beam induced current measurements showed that these pyramids act as high efficient collector of the e-beam excited electron–hole pairs (e–h). This behaviour agrees with the reduction of the cathodoluminescence emission efficiency at the facets. In contrast, a different pyramid type with one enhanced facet is observed at the surface of diodes grown on substrate B. However, these facets have not shown either optic or electric activity. In these diodes, the dislocations localised at the active region degrade the device performance acting as non-radiative recombination centres.

A series of InGaAs/GaAs Single Strained Quantum Wells (SSQWs) with indium content ranging from 25% to 35% and 100 A well thickness were grown on two different (111)B GaAs off-axis substrates under optimized growth conditions for simultaneous growth. Optoelectronic properties were studied in terms of low temperature photoluminescence (PL). Results indicate a PL emission dependence with the substrate used, this dependence being stronger for highly strained systems. In order to determine the source of this dependence, samples were studied by Planar View Transmission Electron Microscopy (PVTEM). Relaxation mechanisms seem to act in a different way regarding the misoriented substrate used. Although previous theoretical results have already reported this dependence, this is the first direct evidence of this phenomenon for SSQWs. The results of these two different techniques will be compared and discussed.

A study by planar view transmission electron microscopy (PVTEM) of crystalline defect types in InGaAs/GaAs MQW grown on GaAs(111)B substrates is presented. The In-content of In x Ga 1− x As layers was increased from x =0.1 to 0.3. The relaxation in structures with low In-content ( x 〈1 1 0〉 directions contained in the interface. However, for In-contents above 22%, a new configuration of MDs as three-pointed star-shaped is observed. These star dislocations were formed by arms parallels to the 〈11 2 〉 directions contained in the growth plane. The interaction between two or more star dislocations worked as a new dislocation multiplication source. These new star dislocations often changed their dislocation lines turning towards the usual 〈1 1 0〉 directions. The characterization of this new dislocation configuration demonstrated that its Burgers vector lay on the growth plane with a strain-relieving component larger than the habitually considered. This result may modify the expectatives of a larger critical layer thickness for InGaAs/GaAs(111)B heterostructures with high In-content.