Kinetics of the evolution of InAs/GaAs quantum dots to quantum rings: A combined x-ray, atomic force microscopy, and photoluminescence study

Abstract

We present an experimental study of the evolution of InAs/GaAs quantum dots partially capped with GaAs, as an annealing process transforms them first into quantum rings and later into holes penetrating the whole cap layer. Shape, composition, and optical emission were monitored as a function of annealing time by means of atomic force microscopy, x-ray photoemission microscopy, and photoluminescence, respectively. Our results show a progressive dissolution of the original dot, with the outdiffused material forming a second wetting layer on the planar region surrounding the dot. For the longest annealing time, in a situation close to thermodynamic equilibrium, no residual dot material is left in the holes, and an In-rich layer covers uniformly the surface. Our findings were examined by taking into account the surface chemical potential previously written for StranskiKrastanov islands partially covered with a cap layer. We show that the energy gain due to the formation of the second wetting layer is the driving force for the shape and composition evolution, but its analytical expression should be modified, with respect to previous formulations, by taking into account the observed material interdiffusion.

Compositional mapping of semiconductor quantum dots and rings

“…The composition measured by XPEEM matches well the one extracted from cross-sectional STM on the residual QD (about 0.55). Very recently the kinetics of the evolution of InAs/GaAs quantum dots to quantum rings has been studied by photoelectron microscopy [134]. The authors presented an experimental study of the evolution of InAs/GaAs quantum dots partially capped with GaAs, as an annealing process transforms them first into quantum rings and later into holes, penetrating the whole cap layer.…”

In-plane mapping of buried InGaAs quantum rings and hybridization effects on the electronic structure

“…Baranwal et al 2 have recently estimated the Indium content, from the center to the edge, in uncapped ring sample by using x-ray photoemission electron microscopy and low energy electron microscopy. The indium concentration has a significant variation in the ring region, once the material is removed from the center to the rim torus-like region, during the dot-to-ring morphological transition.…”

“…Several studies have recently discussed the formation of the QRs in terms of the thermodynamic equilibrium and kinetic transition, but a satisfactory explanation of these processes is still under scrutiny. [2][3][4][5][6][7] This unique toroidal topology displayed by the QRs has also allowed the observation of the Aharonov-Bohm (AB) effect 8 in transport experiments. [9][10][11] Magneto-optical measurements have shown traces of this phenomenon in type-II quantum dots and in charged exciton recombinations in InAs rings.…”

Self-assembled formation and transformation of In/CdZnTe(110) nano-rings into camel-humps

“…Exacerbated diffusion anisotropy in the liquid state, at temperatures above the melting point of In, further distorts the nano-rings into a camel-hump shape. The possibility of using self-assembled semiconductor nano-rings (NRs) as building blocks in new generation solidstate devices, such as quantum computers, 1,2 light emitting diodes (LEDs), 3 and infrared photodetectors, 4 attracts a great deal of interest. Their intriguing topological quantum effects, such as Aharonov-Bohm effect, 5,6 which have been demonstrated both experimentally 7-11 and theoretically, 12,13 drive massive efforts aimed at developing better fabrication techniques, 7,14-17 higher degree of control over size and shape, 1,9,10,18 and ultimately deeper understanding of their formation mechanisms.…”