Combined Structural and Voltage Control of Giant Nonlinearities in Semiconductor Superlattices

Abstract

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.

Sensing nitriles with THz spectroscopy of urine vapours from cancers patients subject to chemotherapy

“…Giant control of the harmonics through a combination of input power and voltage has been predicted in good agreement with experiments recently 18 . We also predict a strong control by manipulating interface scattering asymmetry 23 , as well as a more complex combination of input power and biasing voltage controls 24 .…”

“…Optimization is achieved in a joint effort combining predictive simulations and experiments. The output of the SSLMs is independent of the type of source used to generate input frequency, and both the THz source and heterodyne detection scheme are successfully described by a predictive simulation scheme, that is based on Nonequilibrium Green's Functions (NEGF) calculations and analytical solutions for the Boltzmann equation, as described in detail in the literature [18][19][20][21][22][23][24][25] . It is also possible to extract the relevant parameters from experimental current-voltage curves.…”

“…The experimental data are represented by (green) symbols, and the solid (blue) line is calculated using Refs. [18][19][20][21][22][23][24][25] . Input parameters are obtained from NEGF calculations for the current-voltage using the nominal parameters for the sample, as provided by the sample grower.…”

“…Details of the underlying theory are given in Refs. [18][19][20][21][22][23][24][25] and will not be repeated here. The actual power inside the superlattice is unknown and the best value for α is determined through simulated annealing.…”

Photon Drag Currents and Terahertz Generation in α-Sn/Ge Quantum Wells

“…There the resistance shows also logarithmic temperature dependences which may be attributed to an Altshuler–Aronov effect. Note that the effect can be further enhanced by interface roughness or superlattice design, as noted for the harmonic conversion efficiency in semiconductor superlattices [ 32 , 33 , 34 ] or in graphene chips [ 35 , 36 ]. However, further in-depth studies are required to properly determine the mechanisms for the observed effects and to ascertain the role of α-Sn and topologically inverted band structures for THz generation and photocurrents.…”