Modeling the electronic properties of GaAs polytype nanostructures: Impact of strain on the conduction band character

Abstract

We study the electronic properties of GaAs nanowires composed of both the zincblende and wurtzite modifications using a ten-band k · p model. In the wurtzite phase, two energetically close conduction bands are of importance for the confinement and the energy levels of the electron ground state. These bands form two intersecting potential landscapes for electrons in zincblende/wurtzite nanostructures. The energy difference between the two bands depends sensitively on strain, such that even small strains can reverse the energy ordering of the two bands. This reversal may already be induced by the non-negligible lattice mismatch between the two crystal phases in polytype GaAs nanostructures, a fact that was ignored in previous studies of these structures. We present a systematic study of the influence of intrinsic and extrinsic strain on the electron ground state for both purely zincblende and wurtzite nanowires as well as for polytype superlattices. The coexistence of the two conduction bands and their opposite strain dependence results in complex electronic and optical properties of GaAs polytype nanostructures. In particular, both the energy and the polarization of the lowest intersubband transition depends on the relative fraction of the two crystal phases in the nanowire. arXiv:1704.08499v1 [cond-mat.mes-hall]

High-fidelity optical quantum gates based on type-II double quantum dots in a nanowire

“…We point to that the general conclusions are the same for other combinations of C i values. Evaluation of the precise value of these quantities requires a more detailed band-structure calculation, e.g., in the framework of a multiband k • p model or using ab initio atomistic methods [24][25][26].…”

“…To evaluate the dipole moments, we introduce a full multiband formalism taking into account band-mixing effects. This formalism is compatible with methods such as k • p theory, empirical tight binding, and ab initio [24][25][26], which allow for accurate modeling of excitons in QDs by taking into account detailed electronic band structures. However, to obtain a numerically fast model suitable for design optimization, we perform our dipole moment calculations using a single-band model based on the envelope function and effective mass approximations.…”

Multiband k·p model and fitting scheme for ab initio based electronic structure parameters for wurtzite GaAs

“…On the other hand, the eight-band k • p model has shortcomings that, despite its past and recent successes, make it unsuited for a number of material systems and devices: The limitation of the set of basis functions to the top three valence bands and the bottom conduction band with their respective | ↑ and | ↓ components makes this model a priori unsuited to materials such as GaSb or GaAs in the wurtzite (WZ) phase, where an additional conduction band plays a decisive role [12]. The perturbative approach yields a good description of the electronic band structure around the BZ center, k = 0, whereas the limitation to one conduction band and three valence bands coupled via optical matrix elements cannot resolve all features of the band structure throughout the BZ, so that the description of indirect band gap materials such as Si or Ge, where the minimum of the conduction band is not at the same k value as the maximum of the valence band, requires a larger basis, e.g., a 15-band or even 30-band k • p model [13,14].…”

“…The scope of our work is to provide a versatile tool that can generate parameter sets for k • p models of arbitrary complexity and level of sophistication including, but also going beyond, six or eight basis functions. We focus on WZ GaAs, as this material can be employed in novel nanowire-based crystal-phase heterostructures [18] and the description of its electronic structure requires the consideration of at least one additional conduction band [12,19].…”

Type-II quantum-dot-in-nanowire structures with large oscillator strength for optical quantum gate applications

“…The accurate modeling of excitons in a QD-nanowire system taking into account detailed electronic band structures is possible using methods such as multiband k · p theory, ab initio, and tight-binding calculations [21,24,25]. However, in this work we perform geometrical parameter sweeps to analyze and optimize the device performance, and for this reason we prefer to use a less demanding single-band model based on the envelope function and effective mass approximations.…”