Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy

Abstract

The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As2 source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model a nd realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data

Exciton lifetime and emission polarization dispersion in strongly in-plane asymmetric nanostructures

“…2 in three cross-sections, is a result of noise added to simulate material inhomogeneity as well as intermixing between InAs and the barrier material simulated by Gaussian averaging with standard deviation of 0.6 nm, again supported by the APT data for similar structures. 16 A total of 32 structures were simulated with H varying between 1.8 nm and 3.8 nm nm and L from approximately equal to W up to about 100 nm. In-plane dimensions were read from final material profiles to take into account the fact that intermixing alters small objects relatively stronger than large ones, so using initial spatial extents would be incorrect.…”

Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires

“…3,4 In the past few years, several APT-based studies addressed a limited number of QD structures. [4][5][6][7][8][9][10] Quantum dots can be inserted in semiconductor nanowires either deterministically, with specific shape and composition, [11][12][13][14] or as self-assembled structures. [15][16][17][18] Nanowires, furthermore, represent a model system for atom probe analysis, [19][20][21][22][23][24] as they closely approximate the shape of a field-emission tip.…”

Electronic Structure Calculations of InP-Based Coupled Quantum Dot-Quantum Well Structures

“…However, the QDs with large aspect ratios cannot be completely excluded, since the situation could be changed when the composition distribution within an individual nanostructure is taken into account [13].…”

“…Afterwards, the energy levels are calculated by using the multi-band approach developed by Bahder [12]. The realistic morphological parameters and compositional gradients are possible to be taken into account [13]. All physical parameters are taken after [14], except for the conduction band offset between the QD and the host material.…”