Semiconductor Quantum Dot Superlattices Research Articles

Calculation of strain compensation thickness for III–V semiconductor quantum dot superlattices

Models based on continuum elasticity theory are discussed to calculate the necessary thickness of a strain compensation (SC) layer for a superlattice (SL) of strained quantum wells (QW) or quantum dots (QD). These models are then expanded to cover material systems (substrates, QW or QD, and SC) composed of AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, or InSb, as well as the ternary, quaternary, and higher order material alloys possible in the Al/Ga/In/P/As/Sb systems. SC thickness calculation methods were compared against dynamical scattering simulations and experimental X-ray diffraction measurements of the InAs/GaP/GaAs QD/SC/Substrate superlattices of varying SC thickness. Based on the reduced (but not eliminated) strain present, a further modified strain compensation thickness is calculated to maximize the number of SL repeat units before the onset of misfit dislocations is also calculated. These models have been assembled into a free application on nanoHUB for use by the community.

Time-resolved photoluminescence properties of semiconductor quantum dot superlattices of different microcrystal shapes

We report time-resolved photoluminescence properties on semiconductor quantum dot (QD) superlattices (SLs) using PL lifetime imaging microscopy at a single particle level. PL lifetime imaging technique clearly reveals that different shaped QD SL microcrystals have different time-resolved PL characteristics. The faceted SL microcrystals consisted of well-organized QDs showed faster recombination rates than those of the spherical microparticles including randomly organized QDs, which can be explained by the different degree of energetic couplings among component QDs due to different packing fraction.

Quantum transport in semiconductor quantum dot superlattices: Electron-phonon resonances and polaron effects

Electron transport in periodic quantum dot arrays in the presence of interactions with phonons was investigated using the formalism of nonequilibrium Green's functions. The self-consistent Born approximation was used to model the self-energies. Its validity was checked by comparison with the results obtained by direct diagonalization of the Hamiltonian of interacting electrons and longitudinal optical phonons. The nature of charge transport at electron-phonon resonances was investigated in detail and contributions from scattering and coherent tunneling to the current were identified. It was found that at larger values of the structure period, the main peak in the current-field characteristics exhibits a doublet structure which was shown to be a transport signature of polaron effects. At smaller values of the period, electron-phonon resonances cause multiple peaks in the characteristics. A phenomenological model for treatment of nonuniformities of a realistic quantum dot ensemble was also introduced to estimate the influence of nonuniformities on current-field characteristics.

On the modeling of lattice thermal conductivity in semiconductor quantum dot superlattices

We present a theoretical model for the cross-plane lattice thermal conductivity calculations in semiconductor quantum dot superlattices. Based on continuum approximation, our model takes into account scattering of acoustic phonons on quantum dots. In most practical cases, the dot volume fraction is relatively small and/or dot and host materials have a small acoustic mismatch. This fact lets us take into account only first order scattering events and to significantly simplify the calculations. The results of numerical simulations carried out for Si/Ge quantum dot superlattices show good agreement with experimental data. The proposed model is useful for many applications recently suggested for semiconductor quantum-dot superlattices.

The effect of the long-range order in a quantum dot array on the in-plane lattice thermal conductivity

Semiconductor quantum dot superlattices consisting of arrays of quantum dots have shown great promise for a variety of device applications, including thermoelectric power generation and cooling. In this paper we theoretically investigate the effect of long-range order in a quantum dot array on its in-plane lattice thermal conductivity. It is demonstrated that the long-range order in a quantum dot array enhances acoustic phonon scattering and, thus leads to a decrease of its lattice thermal conductivity. The decrease in the ordered quantum dot array, which acts as a phonon grating, is stronger than that in the disordered one due to the contribution of the coherent scattering term. The numerical calculations were carried out for a structure that consists of multiple layers of Si with layers of ordered Ge quantum dots separated by wetting layers and spacers.

Self-Organization of CdSe Nanocrystallites into Three-Dimensional Quantum Dot Superlattices

The self-organization of CdSe nanocrystallites into three-dimensional semiconductor quantum dot superlattices (colloidal crystals) is demonstrated. The size and spacing of the dots within the superlattice are controlled with near atomic precision. This control is a result of synthetic advances that provide CdSe nanocrystallites that are monodisperse within the limit of atomic roughness. The methodology is not limited to semiconductor quantum dots but provides general procedures for the preparation and characterization of ordered structures of nanocrystallites from a variety of materials.