Self-assembled Quantum Dots: From Stranski–Krastanov to Droplet Epitaxy

Functional materials and devices by self-assembly

“…Self-assembly is a unifying umbrella for a broad range of effects observed in different materials, and there are several excellent reviews discussing self-assembly on molecular, nano-, micro-and macroscopic length scales. 7,[9][10][11][12] Selfassembly is observed in hard condensed-matter systems, such as epitaxial semiconductor quantum dots formed by strain-guided Stranski-Krastanov growth 13 and template-direct eutectics. 14 There are many examples of self-assembled soft-matter systems, with block copolymers 7,11 and DNA origami 15,16 as well-known examples.…”

Anomalous behavior of In adatoms during droplet epitaxy on the AlGaAs surfaces

“…Figure 1(b) and (c) demonstrate that the Al 0.5 Ga 0.5 As and AlAs surfaces on which In droplets are formed in our experiments are very smooth, which means that In droplet characteristics are not influenced by the surface roughness. The sharp RHEED pattern recorded before and directly during the droplet epitaxial growth also indicates an atomically smooth surface [16,23]. Droplets on all three surfaces are spread unevenly over the surface and have a nearly semispherical shape.…”

“…An increase in the Al content in the AlGaAs epitaxial layer from 0% to 100% in case of the Stranski-Krastanov growth leads to a great increase in the density of InAs QDs from 6•10 The reason of this behavior can lie in the difference between the nucleation processes which are different for the Stranski-Krastanov growth and droplet epitaxy [23]. Because droplets are not formed on the surface immediately after In deposition due to the presence of critical thickness [34,49], their parameters can differ depending on a value of the critical thickness for a certain surface.…”

“…Despite the great importance, this issue is still poorly addressed for the In/AlGaAs system. Separate studies of the droplet epitaxial In/AlGaAs growth are presented in the literature [16,22,23], but there is a lack of comparative studies of the growth on surfaces at various Al contents with all other growth conditions being equal. Nevertheless, a study of the Al content influence on In droplet parameters is important in the sense that droplet epitaxy has a number of advantages, such as high quality of structures and good optical characteristics of light-emitting devices [16,[24][25][26][27][28], low QD density when creating single-photon emitters [29][30][31][32], possibility to avoid the formation of a wetting layer [18,[32][33][34][35] which increases the dark current of photodetectors and generally degrades optical characteristics of devices [36,37], etc.…”