Ignition of quantum cascade lasers in a state of oscillating electric field domains

Abstract

Quantum Cascade Lasers (QCLs) are generally designed to avoid negative differential conductivity (NDC) in the vicinity of the operation point in order to prevent instabilities. We demonstrate, that the threshold condition is possible under an inhomogeneous distribution of the electric field (domains) and leads to lasing at an operation point with a voltage bias normally attributed to the NDC region. For our example, a Terahertz QCL operating up to the current maximum temperature of 199 K, the theoretical findings agree well with the experimental observations. In particular, we experimentally observe self-sustained oscillations with GHz frequency before and after threshold. These are attributed to traveling domains by our simulations. Overcoming the design paradigm to avoid NDC may allow for the further optimization of QCLs with less dissipation due to stabilizing background current. arXiv:1806.01828v2 [cond-mat.mes-hall]

The Significance of Carrier Leakage for Stable Lasing in Split-Well Direct Phonon Terahertz Quantum Cascade Lasers

“…This is indication for an effective isolation of the three active laser states from the excited and continuum states, i.e., a clean three laser-level system was obtained in this device. At temperatures close to Tmax, we observe fluctuations in the I-V curves ( Figure 3) indicating lasing instability [24,9]. The occurrence of fluctuations in the I-V curves is correlated with the disappearance of the second slope from the L-I curves in the vicinity of Tmax and to fast deterioration of the laser intensity ( Figure 2).…”

“…In devices with more tendency for intramodule leakage due to lower radiative barriers such as Device 2 (wafer VB0837 in Albo et al [8], Tables 1 and 2), hot electrons could relax more easily through leakage paths (as scattering from the ULL to level 7 in Figure 1 in [8]) and the instability was much more moderate. The main reason for the laser instability may be the formation of electric field domains [9,10] in the NDR region in the absence of parallel leakage channels.…”

“…Here, we studied different realizations of the SWDP scheme using different barrier compositions than the original contribution and analyzed their performance. We found that the lasers are limited by a lasing instability [9,10] that becomes significant as the temperature increases.…”

Uncovering spatiotemporal patterns in semiconductor superlattices by efficient data processing tools

“…In principle, it should be possible to find inhomogeneous Bloch oscillations that coexist with much slower self-sustained oscillations due to periodic generation and motion of charge dipoles [3]. In experiments, the frequency range of the more robust selfsustained oscillations in semiconductor superlattices may be as large as 100-200 GHz, which makes them useful in, e.g., fast oscillators and detectors [4], whereas similar selfsustained oscillations in quantum cascade laser devices may reach ultrahigh frequencies well in the THz range [5], which are needed in, e.g., nanopatterned antennas [6]. Superlatticebased devices exhibit very different spatiotemporal patterns and rich nonlinear dynamics, including static high-field domains, excitability due to collective charge dynamics, as well as self-sustained periodic, quasiperiodic, and chaotic current oscillations [4,[7][8][9][10].…”

Uncovering spatio-temporal patterns in semiconductor superlattices by efficient data processing tools

“…In principle, it should be possible to find inhomogeneous Bloch oscillations that coexist with much slower self-sustained oscillations due to periodic generation and motion of charge dipoles [3]. In experiments, the frequency range of the more robust self-sustained oscillations in semiconductor superlattices may be as large as 100-200 GHz, which makes them useful in, e.g., fast oscillators and detectors [4], whereas similar self-sustained oscillations in quantum cascade laser devices may reach ultra-high frequencies well in the THz range [5], which are needed in, e.g., nano-patterned antennas [6]. Superlattice-based devices exhibit very different spatio-temporal patterns and rich nonlinear dynamics, including static high-field domains, excitability due to collective charge dynamics, as well as self-sustained periodic, quasi-periodic, and chaotic current oscillations [4,[7][8][9][10].…”