Investigation of strain in self-assembled multilayer InAs/GaAs quantum dot heterostructures

Inhibition of emission wavelength blueshift in annealed InAs/GaAs quantum dot stacks: an important observation for their potential application in photovoltaic devices

“…The emergence of these multiple peaks in the PL spectrum may be due to the multimodal distribution of the QDs in the as-grown sample. From our previous work [10] on stacked InAs/GaAs MQD, it can be presumed that one of the peaks in the PL spectrum of Fig. 3(a) might have resulted due to emission of the QDs present in the incomplete stacks of the MQD sample.…”

“…The randomly distributed inhomogeneous strain field [15,16] produced by the underlying QDs can be attributed for the vertical coupling between layers as it provides the driving force for the nucleation of the upper QDs. It is to be mentioned here that on increasing the number of QD stacks the overall accumulated homogeneous strain in the heterostructure increases [10], which limit the stacking number in a multilayer QD system. The micrograph of as-grown sample in Fig.…”

“…Figure 1 illustrates schematic diagram of the sample. The 2.7 ML InAs QDs in the 10-layer stacked heterostructure were grown at a 0.2 ML/sec growth rate at 520 • C. The QDs were overgrown with a combination capping of 30 Å quaternary In 0.21 Al 0.21 Ga 0.58 As and a thick GaAs spacer (180 Å) grown at 520 • C. The capping layers were subsequently annealed at 590 • C. Details of the sample growth can be found in [10]. Small pieces were cut from the central region of the MBE grown wafer and were subjected to ex situ rapid thermal annealing (RTA) under GaAs proximity capping in argon ambient.…”

“…We already have reported that a combination barrier of quaternary InAlGaAs and GaAs can be used in order to get stacked and vertically aligned multilayer QDs and the accumulated strain in the multilayer QD (MQD) heterostructure decreases with an increase of combination barrier thickness [10,11]. This MQD structure can be used for IBSC solar cells by embedding in the GaAs host matrix.…”

Self‐assembled InGaAs/GaAs quantum dot photodetector on germanium substrate

“…The relatively high dark current density of the device is due to the increased In/Ga intermixing in upper layers of the stacked QDs because of accumulated strain in the QD stacks, which may be either due to the heteroepitaxial growth of GaAs on Ge substrate [11] or, due to nonuniform distribution of strains in stacked multilayer heterostructures of two dissimilar lattice mismatched materials [12,13] or, both. In order to decrease the dark current it is therefore critical to counteract the strain induced In/Ga intermixing by further optimising the growth parameters of the InGaAs QD heterostructure.…”