A comparative analysis of analog and digital alloy technique of InxGa1-xAs capping material on InAs quantum dot heterostructures

Abstract

In this study, the concept of analog and digital alloy capping with ternary alloy InxGa1-xAs has been utilized in capping layer of InAs QDs. The composition of indium (In) in the capping layer having thickness of 8 nm, was kept constant in case of analog alloy technique. While, in digital alloy technique, In composition was varied from 0.45 to 0.15 in steps of 0.10 (Structure D1) having a thickness of 2 nm each. Validation of simulated results with previous experimental data was carried out to check accuracy of the present work. The hydrostatic and biaxial strains in growth direction were computed and compared. The magnitude of hydrostatic strain is reduced by 4.115% and biaxial strain is increased by 0.62% in the QD region of structure D1 as compared to structure A1. This indicates better carrier confinement and longer emission wavelength in structure D1 as compared to structure A1. Structure D1 provided an increment of hydrostatic strain by 3.41% and a decrement of biaxial strain by 2.56% in the QD region as compared to structure A2. Structure D1 with digital capping alloy provides a gradual strain relaxation in the capping layer due to systematic variation of In composition, ensures strain relaxation profile throughout the heterostructure by minimizing the lattice disparity in subcapping layers. The computed emission wavelength of structure A1, A2, and D1 were 1224, 1313, and 1287 nm respectively. The digital alloy technique would help in minimizing strain distribution within the heterostructure and results in defect and dislocation free heterostructure.