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.
Highlights
We are not interested in circuit-equivalent approaches which might be reliable for a quasi-classical solid state oscillator9 but which are not predictive if spontaneous frequency multiplication effect takes place.3,4 we adopt another way in which we describe an optical method to precisely determine the intrinsic conversion efficiency of the excited SL sample
Among the results presented here, we highlight: (i) Transport and power emission calculations under the additional influence of the asymmetry in current flow induced by interface roughness scattering. (ii) Harmonic power efficiency calculated directly from the Poynting vector, by estimating the field inside the sample with results consistent with measurements found in the literature for odd harmonics. (iii) Study of the predicted efficiency for even harmonics as a function of controlled symmetry breaking at the current flow level
We demonstrate that a semiconductor superlattice allows the conversion of input power to third-harmonic radiation with an efficiency of about 2 %
Summary
We are not interested in circuit-equivalent approaches which might be reliable for a quasi-classical solid state oscillator9 but which are not predictive if spontaneous frequency multiplication effect takes place.3,4 we adopt another way in which we describe an optical method to precisely determine the intrinsic conversion efficiency of the excited SL sample (see Fig. 1). Previous studies, which could only predict odd harmonics, in contrast to our more complete approach, have demonstrated that the frequency multiplication mechanism stems from possible the direct interaction of the input field with Bloch oscillating electrons.21 The exact condition which determines the onset of Bloch oscillations in a SL for an unbiased oscillating field corresponds to the critical value of ac = Uc/hν, where the input field amplitude (Eac) equals the critical field Uc/(ed) after which the static I-V shows NDC.
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