Misfit management for reduced dislocation formation in epitaxial quantum-dot-based devices

The improved control of lattice strain in the quantum-dot (QD) region of p–i–n structures using a modified epitaxial growth procedure has been observed and analyzed. Strain in the QD region was managed by (a) inserting a correction layer (CL) with a lattice constant that was intermediate between the lattice constant of the QD region and the lattice constant of the underlying substrate, (b) capping the QD islands with a layer that had the same lattice constant as the CL, and (c) the utilization of only three atomic elements in the growth of the QD intrinsic region. These results were demonstrated in InxGa1−xAs/InAs/InxGa1−xAs p–i–n devices with five InAs QD layers and then compared with InxGa1−xAs p–n (HOM) devices with identical ternary alloy compositions and no quantum dot layers. The layers in all of the devices were grown by molecular beam epitaxy. X-ray diffraction (XRD) measurements showed the interface dislocations in the QD samples were fewer than in the HOM samples and were isolated at the InxGa1−xAs–GaAs interface, away from the optically active QD region. Cross-sectional, high-resolution transmission electron microscopy (HRTEM) images showed no evidence of threading dislocations in the QD region. Post-growth calculations of the average lattice constant of the QD region, using atomic force microscopy, XRD, and HRTEM data, indicated the QD region experienced a ∼3× reduction in its lattice misfit while increasing its critical thickness by more than 3×. Although the total misfit in the QD samples increased with the insertion of the CL and the average lattice constant of the QD region was not matched to the CL, the strain energy nevertheless was absorbed successfully without creating deleterious dislocations as seen in QD devices exhibiting lower dark current densities than in HOM control devices.

► Lattice strain dynamics of dislocation mechanisms and management were examined and tested.
► Fewer defects in quantum-dot based devices through misfit strain mitigation was demonstrated.
► Quantum-confined p–i–n devices exhibited lower dark current densities than p–n solar-cell devices.
► Quantum-dot InGaAs/GaAs p–i–n devices were compared to p–n devices without quantum dots.
► Misfit management leading to improved optoelectronic performance was shown.