# Controlling the harmonic conversion efficiency in semiconductor superlattices by interface roughness design

## TL;DR

This paper investigates how interface roughness affects harmonic generation efficiency in semiconductor superlattices, providing a predictive model that aligns with experimental data and suggests ways to optimize even harmonic output.

## Contribution

It introduces a theoretical approach that includes interface imperfections to predict power conversion efficiency and enables design of superlattices for targeted harmonic outputs.

## Key findings

- Interface roughness significantly influences harmonic output efficiency.
- The model accurately predicts odd harmonic outputs across a wide frequency range.
- Controlling interface quality can enhance even harmonic power generation.

## Abstract

In semiconductor superlattices, when Bragg oscillating electrons interact with an input electromagnetic field, frequency multiplication is possible. An ideal superlattice has a purely antisymmetric voltage current response and can thus produce only odd harmonics. However, real world superlattices can also have even harmonic response and that increases the range of possible output frequencies. These effects have been recently explained with a predictive model that combines an Ansatz solution for the Boltzmann Equation with a Nonequilibrium Green's Functions approach. This predictive tool, coupled with recent progress on GHz input sources, support the growing interest in developing compact room temperature devices that can operate from the GHz to the THz range. The natural question to ask is what efficiencies can be expected. This paper addresses this issue by investigating power-conversion efficiency in irradiated semiconductor superlattices. Interface imperfections are consistently included in the theory and they strongly influence the power output of both odd and even harmonics. Good agreement is obtained for predicted odd harmonic outputs with experimental data for a wide frequency range. The intrinsic conversion efficiency used is based on the estimated amplitude of the input field inside the sample and thus independent of geometrical factors that characterize different setups. The method opens the possibility of designing even harmonic output power by controlling the interface quality.

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Source: https://tomesphere.com/paper/1901.02654