Theoretical analysis of influence of random alloy fluctuations on the optoelectronic properties of site-controlled (111)-oriented InGaAs/GaAs quantum dots

Abstract

We use an sp 3 d 5 s * tight-binding model to investigate the electronic and optical properties of realistic site-controlled (111)-oriented InGaAs/GaAs quantum dots. Special attention is paid to the impact of random alloy fluctuations on key factors that determine the fine-structure splitting in these systems. Using a pure InAs/GaAs quantum dot as a reference system, we show that the combination of spin-orbit coupling and biaxial strain effects can lead to sizeable spin-splitting effects in these systems. Then, a realistic alloyed InGaAs/GaAs quantum dot with 25% InAs content is studied. Our analysis reveals that the impact of random alloy fluctuations on the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots reduces strongly as the lateral size of the dot increases and approaches realistic sizes. For instance the optical matrix element shows an almost vanishing anisotropy in the (111)-growth plane. Furthermore, conduction and valence band mixing effects in the system under consideration are strongly reduced compared to standard (100)-oriented InGaAs/GaAs systems. All these factors strongly indicate a reduced fine structure splitting in site-controlled (111)-oriented InGaAs/GaAs quantum dots. Thus, we conclude that quantum dots with realistic (50-80 nm) base length represent promising candidates for polarization entangled photon generation, consistent with recent experimental data.

Fully analytic valence force field model for the elastic and inner elastic properties of diamond and zincblende crystals

“…Note that eqs. (24)(25)(26)(27) are identical to the covalent equations (eqs. (17)(18)(19)(20)) apart from the electrostatic addi- tion; the non-Coulombic case can be recovered by setting S = 0.…”

“…Force constants and effective charge parameters for selected III-V materials obtained from eqs. (24)(25)(26)(27) are given in Table III.…”

“…Substituting the value for S thus obtained into eqs. (24)(25)(26)(27) yields the required potential. With this potential, all elastic properties input are reproduced exactly, as is ω TO , through the inner elastic con-…”

“…Because of these advantages, the Keating potential remains widely used for the calculation of strain and atomistic relaxation in large systems, such as semiconductor quantum dots comprising millions of atoms. [24][25][26][27] Unfortunately, to describe the elasticity of cubic crystals fully requires more than two elastic constants (and more than two force constants), and the Keating potential fares less well for materials other than Si. For heteropolar materials errors in C 44 grow with ionicity, and these errors manifest in the inaccurate modelling of systems where shear strains or internal relaxations are important.…”

Tight-binding description of inorganic lead halide perovskites in cubic phase

“…The empirical tight-binding method with sp 3 d 5 s * basis in the nearest neighbor approximation gives a precise description of band structure of bulk III-V [13] and group IV [14] semiconductors. It has a long history of application for the nanostructures [15][16][17][18][19][20]. The parameters of the method may be in principle extracted from the DFT calculations [21][22][23] which makes this method an atomistic interpolation of underlying DFT model.…”