Defect investigation of stacked self-assembled InAs/GaAs quantum dot lasers

Two classes of stacked structures with (i) varying InAs nominal thickness θ but fixed GaAs ''spacer'' layer (d = 25 nm), and (ii) a varying d but fixed InAs nominal thickness (θ = 2.73 monolayers (ML)) were grown by solid-source molecular beam epitaxy (MBE). The formation of large 'volcano-like' defects with stacking faults and dislocations, penetrating several layers into the stack, was observed for a nominal InAs deposition of 2.73 ML and 3.62 ML in case (i). In case (ii), with, d = 50 nm, a dramatic improvement in structural integrity was observed with the absence of the 'volcano-like' defect. The Photoluminescence (PL) intensity where, d=50 nm, was almost 132 times stronger for, θ=3.64 ML, indicating that the improvement in crystal structure resulted in better PL efficiencies. Remarkably, significant improvements in PL intensity were observed when the material was etched to selectively remove the topmost stacks thus demonstrating that the 'volcano-like' defects were responsible for the severely suppressed PL efficiencies. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)