InAs QDs in a metamorphic In$_{0.25}$Ga$_{0.75}$As matrix, grown by MOCVD

InAs quantum dots (QDs) in a metamorphic InGaAs matrix are grown by MOVPE (metal-organic vapor-phase epitaxy) on GaAs substrates. The QDs emit light in the range 1380–1400 nm at room temperature. A multilayer metamorphic buffer (MB) consisting of nine sublayers, each having a thickness of $\sim$200 nm, is used to grow the structures. In each of the first seven sublayers, the indium content x successively increases by $\sim$3.5% to reach a final value of 24.5%. Then a compensating sublayer with $x$ = 28% and a final dislocation-free sublayer with $x$ = 24.5% are grown. It is shown that the elastic strain relaxes with dislocation bending at both interfaces in the third, from the surface, sublayer, with the top layer being free of dislocations at both interfaces. The QDs are formed in the metamorphic matrix by the deposition of 2–2.5 InAs single layers at 520$^\circ$C, with the subsequent overgrowth of a thin InGaAs layer (cap layer) at the same temperature. It is found that, to improve the optical and structural quality of the samples, it is necessary to raise the growth rate and reduce the concentration of indium in the cap layer with respect to the corresponding growth parameters of the last layer of the metamorphic buffer.