Self-assembled GaAs/AlGaAs coupled quantum ring-disk structures by droplet epitaxy

Abstract

The fabrication, by droplet epitaxy, of a class of quantum nanostructures characterized by a regular, nanometres high, flat disks with a diameter of hundreds of nanometres and a hole at the centre encircled by a ring a few nanometres high, is presented here. A detailed analysis of the growth kinetics performed via in situ and ex situ probes allows us to propose a working model for the formation of these structures.

Unified model of droplet epitaxy for compound semiconductor nanostructures: Experiments and theory

“…The TEM top views of islands from sample A, obtained with diffraction vector g = [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] clearly show Moiré fringes, due to the interference between the crystal lattice of the island (GaAs) and that the Si substrate ( Figure 11). EDS map scans show the same distribution of the Ga and As signals, which mimics the island shape, thus demonstrating the correct stoichiometry of the GaAs all over the island volume -i.e.…”

“…Subsequent exposure of the liquid droplets to the group V vapor causes them to crystallize into quantum dots, by which we mean compact, threedimensional nanostructure 5,6 . A variety of nanostructures may be obtained using this technique, ranging from compact quantum dots, quantum rings, and core shell structures [6][7][8][9][10][11] . While experimental observations evoke likely mechanisms, a unified model for the formation of various nanostructural morphologies via DE is still needed.…”

Precise shape engineering of epitaxial quantum dots by growth kinetics

“…A III-column element molecular beam is initially supplied for the formation of droplets on the substrate surface in vacuum, and subsequently an As flux is used for the crystallization of droplets into the III-As nanostructures. With a suitable selection of growth conditions, and by carefully controlling the group-III crystallization kinetics into a III-V semiconductor, it is possible to engineer the final shape of the nanocrystals from islands [25,[27][28][29], rings [30,31], wires [32,33], and even more complex structures [34][35][36][37][38][39].…”

The exciton structure and optical properties of semiconductor nanodots and nanorings

“…Kapljična epitaksija je intenzivno izučavan metod za narastanje nanotačaka, a uz izvesne modifikacije se već više od decenije primenjuje za proizvodnju sistema nenapregnutih nanotačaka, a najčešće sistema baziranih na GaAs/(Al,Ga)As (Somaschini et al, 2010). Kako u procesu narastanja ne postoji naprezanje materijala, javlja se tendencija formiranja slojevite 2D strukture.…”

“…nanodisk on nanoring-NON ili coupled ring disk-CRD) (Somaschini et al, 2010), ili njima srodne strukture sa smanjenom debljinom sloja unutar prstena i obodom velikog radijusa (sl. 1.8(d)).…”