Cathodoluminescence study of band filling and carrier thermalization in GaAs/AlGaAs quantum boxes

Abstract

We have examined carrier thermalization, recombination, and band filling in GaAs/AlGaAs quantum boxes with low-temperature cathodoluminescence ͑CL͒. The temperature dependence of the quantum box CL intensity for Tр 90 K exhibits an Arrhenius behavior, as a result of carrier thermalization between the quantum box and surrounding barrier regions. The width of the quantum box luminescence is found to increase rapidly with an increasing excitation density and reveals an enhanced phase-space and real-space filling, in comparison to the behavior observed for quantum wells.

Mesa-top quantum dot single photon emitter arrays: Growth, optical characteristics, and the simulated optical response of integrated dielectric nanoantenna-waveguide systems

“…2 serve as the basic units which, appropriately interconnected, will enable the next level of hierarchical design enabling SQD-SQD communication, and thus the creation of optical circuits ( Substrate-encoded size-reducing epitaxy 23 is an approach to growth-controlled spatially-selective formation of nanostructures that exploits growth on designed non-planar patterned substrates, i.e. patterned structurally such that the tailored surface curvature induces surface stress gradients (capillarity) that direct adatoms during deposition preferentially to mesa tops [23][24][31][32][33][34][35] or valleys 23,36 / recesses 37,38 for selective incorporation through control on the relative kinetics of adatom incorporation on the contiguous facets present in the designed curvature 23,[31][32][33][34][35] . For pattern designs that induce net migration from the side facets to the mesa top, preferential incorporation at the mesa-top leads to growth-controlled mesa size reduction, enabling in-situ preparation of contamination and defect-free nanomesa arrays from the as-patterned array via homoepitaxy.…”

“…Subsequent heteroepitaxy, lattice matched or mismatched, then enables synthesis of quantum confined nanostructures such as quantum wires and dots on pristine nanotemplates 23 . For the technologically important (001) surface oriented substrates of the tetrahedrally-bonded semiconductors of groups IV, III-V, and II-VI, the <100> edge orientations of square mesas provide four-fold symmetry and thus potentially symmetric migration of adatoms from the sidewalls to the top (Fig.3a) to reduce, in-situ, the as-patterned mesa top size to the desired size utilizing homoepitaxy under controlled growth kinetics 23,24,[31][32][33] . Indeed, depending upon the chosen as-etched sidewall crystallographic planes, the size-reducing growth can offer more than one pinch-off stages 33 , thereby allowing control on not only size but also the shape of the QD formed subsequently via heteroepitaxy as depicted in Fig.3 , both synthesized using solid-source molecular beam epitaxy (SSMBE).…”

“…For the technologically important (001) surface oriented substrates of the tetrahedrally-bonded semiconductors of groups IV, III-V, and II-VI, the <100> edge orientations of square mesas provide four-fold symmetry and thus potentially symmetric migration of adatoms from the sidewalls to the top (Fig.3a) to reduce, in-situ, the as-patterned mesa top size to the desired size utilizing homoepitaxy under controlled growth kinetics 23,24,[31][32][33] . Indeed, depending upon the chosen as-etched sidewall crystallographic planes, the size-reducing growth can offer more than one pinch-off stages 33 , thereby allowing control on not only size but also the shape of the QD formed subsequently via heteroepitaxy as depicted in Fig.3 , both synthesized using solid-source molecular beam epitaxy (SSMBE). The flat morphology and the absence of defects for lattice mismatched QD 32 are due to a substantial strain relaxation on a sufficiently small nanoscale mesa owing to the presence of mesa free sidewalls as demonstrated in multi-million atom molecular dynamics simulations 34,35 .…”

“…Finally, we note that SESRE not only permits control on mesa-top SQD shape and size, it also allows controlled vertical stacking and coupling of QDs, as desired 31,32 . Moreover, unlike other template-directed growth approaches that often suffer from formation of unintended parasitic nanoscale structures, SESRE carried out on properly chosen mesa orientations and shapes under careful control of growth kinetics leads only to the formation of predictable and intended structures 23,32,33 . The controlled formation of uniform SESRE QD array, however, requires atomistic level control on the growth kinetics and nanometer precision of the starting mesa lateral size.…”

“…3a) to reduce, in-situ, the as-patterned mesa top size to the desired size utilizing homoepitaxy under controlled growth kinetics 23,24,[31][32][33] . Indeed, depending upon the chosen as-etched sidewall crystallographic planes, the size-reducing growth can offer more than one pinch-off stages 33 , thereby allowing control on not only size but also the shape of the QD formed subsequently via heteroepitaxy as depicted in Fig. 3 (b) and (c).…”