A systematic post-growth thermal annealing step for receding size inhomogeneity inside multiple InAs/In<inf>x</inf>(Ga)<inf>1-x</inf>As sub-monolayer quantum dot layers

In-Ga intermixing occurrence in InAs/In(Ga)As sub-monolayer (SML) quantum dots (QDs) is very consequential for the understanding of some optoelectronic properties. In this current study, we have performed a rapid thermal annealing (RTA) process at various annealing temperatures (Ta: 650 - 800°C) on multiple SML QD layers (4,6,8,10) grown at 490°C by Molecular - beam Epitaxy (MBE) technique and it has led to some positive conclusions on the analysis of 19 K photoluminescence (PL) data. A blueshift in the ground-state PL peak indicates the formation of smaller - sized dots and at the same time we see the full - width at half - maximum (FWHM) gets narrowed down through annealing suggesting for uniform dot size distribution. It is noteworthy to mention that samples with 4 and 6 QD layers showed a same degree of In-Ga intermixing when compared to asgrown (ASG) samples (62 meV), while 8 and 10 QD layers was changeable due to multimodal dot characteristics and perhaps the intermixing induced defects. This derives to conclude that the latter possess more QD size inhomogeneity issues and it can affect the charge carrier confinement energy. The FWHM broadening seen in 8 and 10 QD layers will lead to the formation of broader electronic minibands as dots of various size distributions merge altogether from these vertically - aligned layers with increase in Ta, while the redistribution of thermal mass transport species led to a narrower FWHM in 4 and 6 QD layers (and discrete energy states). Also, In-Ga intermixing effects are more pronounced in 8 and 10 stacks encouraging the defect creation. Hence, for the fabrication of room-temperature high gain infrared photodetectors (IRPDs), samples containing 4 and 6 QD layers with higher thermal stability against annealing (at 700°C) are the best candidates.