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

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. High power coherent sources for the whole Gigahertz (GHz)-Terahertz (THz) -Mid Infrared (MIR) ranges, operating at room temperature are in demand for a myriad of applications and nonlinear effects are evolving into the dominant solutions. Difference frequency generation via resonant optical nonlinearities pumped by a MIR quantum cascade laser [1] is encouraging for the THz-MIR. The combination of input from superlattice electronic devices (SLEDs) [2] with semiconductor superlattice (SSL) multipliers [3, 4] is highly promising since for the GHz-THz: (i) SLEDS have reached a record 4.2 mW power output in the fundamental mode at 145 GHz at room temperature [2]. (ii) Synchronization between SLLs leads to a dramatic increase in output power [5]. From a fundamental point of view, nonlinearities in SSLs provide numerous opportunities to create and develop spectroscopic schemes, including harmonic generation, mixing, detecting and parametric

Giant controllable gigahertz to terahertz nonlinearities in superlattices

“…The experiments have been performed with GHz input leading to THz output, demonstrating full control and enhancement of the nonlinearities in terms of applied voltage and power, in a regime that can be studied with input fields from compact devices 19,20 . A clear-cut proof of the role of asymmetric flow in our own data is highlighted in Fig.…”

“…References 18 , 19 summarize the realistic HHG efficiencies that can be achieved by coupling unbiased SSLMs with the most relevant commercially available compact GHz input sources. These type of devices exploit the radiation at odd harmonics of the input oscillating field, originating from the phase-modulated Bloch oscillations and under the assumption of a uniform electric-field distribution across the SSL sample.…”

Potential and limits of superlattice multipliers coupled to different input power sources

“…3,49 However, by considering the influence of the asymmetry in current flow induced by interface roughness scattering, even harmonic generation can emerge. 2,5,39 The V-I characteristics described by Eq. (1) then should be modified according to…”

“…The conversion efficiency of even harmonics for an unbiased SL multiplier is far weaker from the performance of other available material systems. 9 Nevertheless, as has been discussed recently, 39 the optimization of the asymmetric effects in a heterostructure semiconductor, i.e. a systematic interface roughness design, can lead to significant enhancement of even harmonic output power.…”

Optical Transistor for Amplification of Radiation in a Broadband Terahertz Domain

“…Graphene and carbon nanotubes may serve as highly tunable sources and detectors of THz radiation [28][29][30][31][32][33][34], and even in THz lasers [35][36][37][38][39][40]. In the dual-gate graphene-channel field-effect transistor [41] embedded into a cavity resonator [42,43], one observes spontaneous broadband light emission in the 0.1-7.6 THz range with the maximum radiation power of ∼ 10 µW at the temperature 100 K. There are also emerging sources of THz radiation that operate at room temperature and can deliver several frequencies, e.g., multiple harmonic generation in superlattices that can also be made compact by coupling with a sled [44,45], frequency difference generation in mid infrared QCLs leading to tunable THz radiation [46] and THz optical combs [47].…”