A comparative study of analog and digital alloy technique of InxGa1-xAs well material on InAs/InGaAs DWELL heterostructures

Abstract

We present a new concept of strain minimization through digital alloy capping layer (DACL) for the dot-in-a-well (DWELL) heterostructure. In this work, three different DWELL heterostructures with ternary capping of In_xGa_1-xAs have been simulated. The two analog DWELL structures with the indium (In) composition of 15% (Sample A1) and 45% (Sample A2), and one digital DWELL structure (Sample D1) with varying In composition from 45% to 15% in steps of 10 are considered. The bottom and top InGaAs well layer thickness of QD is considered to be 8 nm each. In digital sample D1, the bottom and top well layer is equally divided into 4 sub-parts, each having the thickness of 2 nm. The biaxial strain in sample D1 is increased by 0.66% and reduced by 2.95% and hydrostatic strain in sample D1 is reduced by 5.14% and increased by 3.49% when compare to their analog counterparts A1 and A2 respectively. Higher biaxial strain indicates the increased spacing between the heavy-hole and light-hole band in valence band, which would result in red-shifted photoluminescence. Lower hydrostatic strain ensures deeper electrostatic potential facilitating higher activation energy. The sample D1 provides the gradual strain relaxation inside the top and bottom InGaAs well layer. The emission wavelength of 1394, 1547, and 1514 nm is observed for samples A1, A2 and D1 respectively. The overall strain distribution inside the heterostructure is smoothly minimized in steps which would result in defect free heterostructure and hence will provide longer emission wavelength for SWIR applications.