Combined Structural and Voltage Control of Giant Nonlinearities in Semiconductor Superlattices

Recent studies have predicted a strong increase in high harmonic emission in unbiased semiconductor superlattices due to asymmetric current flow. In parallel, an external static bias has led to orders of magnitude control of high harmonics. Here, we study how this control can affect the operation of superlattice multipliers in a range of input frequencies and powers delivered by commercially available GHz sources. We show that the strongly nonlinear behavior can lead to a very complex scenario. Furthermore, it is natural to ask what happens when we combine both asymmetry and voltage control effects. This question is answered by the simulations presented in this study. The efficiency of high-order even harmonics is increased by the combined effects. Furthermore, the development of ‘petals’ in high-order emission is shown to be more easily achieved, opening the possibility to very interesting fundamental physics studies and more efficient devices for the GHz–THz range.

Heteroepitaxial van der Waals semiconductor superlattices

We report atomic layer-by-layer epitaxial growth of van der Waals (vdW) semiconductor superlattices (SLs) with programmable stacking periodicities, composed of more than two kinds of dissimilar transition-metal dichalcogenide monolayers (MLs), such as MoS2, WS2 and WSe2. The kinetics-controlled vdW epitaxy in the near equilibrium limit by metalorganic chemical vapour depositions enables to achieve accurate ML-by-ML stacking, free of interlayer atomic mixing, resulting in the tunable two-dimensional (2D) vdW electronic systems. We identified coherent atomic stacking orders at the vdW heterointerfaces, and present scaling valley polarized optical excitations that only pertain to a series of 2D type II band alignments.

Effective Simulations of Electronic Transport in 2D Structures Based on Semiconductor Superlattice Infinite Model

Effective simulations of semiconductor superlattices are presented in the paper. The simulations have been based on the Wannier function method approach where a new algorithm, inspired by Büttiker probes, has been incorporated into determining the Green function procedure. The program is of a modular structure, and its modules can either work independently, or interact with each other following a predefined algorithm. Such structuring not only accelerates simulations and makes the transport parameters possible to initially assess, but also enables accurate analysis of quantum phenomena occurring in semiconductor superlattices. In this paper, the capabilities of type I superlattice simulator, developed earlier, are presented, with particular emphasis on the new block where the Fermi levels are determined by applying Büttiker probes. The algorithms and methods used in the program are briefly described in the further chapters of our work, where we also provide graphics illustrating the results obtained for the simulated structures known from the literature.