Abstract
Tuning the wavelength of emitted radiation is a tremendous feature of quantum cascade lasers which enables their use in various applications. Usually, this tuning is executed by the change of the bias current or the temperature. In this paper, it is demonstrated, both experimentally and theoretically, that yet another possibility of tuning laser wavelength offers the change of doping density. For the experimental demonstration, a set of GaAs/AlGaAs devices emitting in the range 9.3–9.7 µ{rm {m}} was MBE grown and processed. For the theoretical analysis, the simulations that employ nonequilibrium Green’s function formalism, applied to the single-band effective mass Hamiltonian, are used. The analysis shows that the physical mechanism responsible for wavelength-doping correlation is a linear Stark effect. The range of tuning is limited on both low and high doping side. Both these limits are established and discussed.
Highlights
The well-known feature of a quantum cascade laser (QCL), which enables this device being used in gas tracing systems, is the possibility of tuning the wavelength of the emitted radiation
In QCL, the transport is governed by the scattering-assisted resonant tunneling through the injection barrier, which is well described by the Kazarinov–Suris formula [27]: J
We have characterized in detail QCL wavelength tuning by the injector doping
Summary
The well-known feature of a quantum cascade laser (QCL), which enables this device being used in gas tracing systems, is the possibility of tuning the wavelength of the emitted radiation. The wavelength of a QCL is tuned by changing either the laser temperature and/or the bias current [1]. Temperature tuning provides a broad tuning range; it is slow as the whole submount and laser needs to be temperature-controlled. Through the use of a buried heater element, the active region temperature can be modified without changing the submount one. This method has been successfully applied to buried heterostructure lasers, becoming an attractive solution for molecular spectroscopy [2]. The short period length and the diagonal nature of the laser transitions in QCLs guarantee an additional tuning mechanism of the emission due to the linear Stark effect [3]
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