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2Long-wavelength emitters based on HgTe/CdHgTe quantum wells: luminescence, stimulated emission, lasers
S. Morozov
Institute for Physics of Microstructures of Russian Academy of Sciences, Nizhniy Novgorod, Russia
Heterostructures with quantum wells (QW) Hg(Cd)Te/CdHgTe are attractive as a material for mid-infrared (IR) lasers. Due to the progress of the molecular beam epitaxy (MBE), HgCdTe-based structures are of high quality, which is confirmed by recent studies of the Urbach energy [1]. The presence of a quasirelativistic law of carrier dispersion makes it possible to suppress the Auger process that prevents radiative recombination [2]. This is also why special attention is paid to the wavelength range, where quantum cascade lasers (QCL) are currently unavailable. It is well known that in the IR region of 20-60 jum, they can provide generation only at certain wavelengths, which is determined by the strong resolution of absorption in most A3B5 semiconductors used to create them. Interband lasers based on Hg(Cd)Te/CdHgTe can serve as an alternative, another advantage of which in comparison with QCLs is the continuous tuning of the wavelength. At the moment, stimulated emission (SE) in HgCdTe QW structures has been demonstrated beyond 24 jum, namely at 31 pm [2], however, the range between 24 and 31 ym has not been fully covered.
The studied structures were grown by the MBE on GaAs substrate (013). The structures contain a 50 nm ZnTe-buffer, followed by a CdTe-buffer with a thickness of Dbuf and waveguide layers of Cd1-yHgyTe with 15 QW Hg1_xCdxTe with a thickness of d [3].
The SE spectra are studied using a Bruker Vertex 80v Fourier spectrometer in step-by-step scanning mode. The spectrometer is optically coupled using an elliptical mirror with a closed-cycle helium cryostat, which has the ability to adjust the temperature in the range of 8-300 K [2].
In this work we demonstrate SE of HgCdTe QWs structures at wavelengths of 31 and 27 ym with pulsed optical pumping, which are not used by existing QCLs. Optimization of the waveguide layer led to a decrease in mode losses and, as a consequence, to the production of SE in the range of 27-18 jum with pulsed optical pumping and 24-20 ym with continuous optical pumping with temperature adjustment. The reduction of mode losses and the use of quasi-continuous pumping, which makes it possible to accumulate carriers at dimensional quantization levels for an arbitrarily long time to obtain population inversion, with an optical pulse time greater than the radiative time of the interband transition in the case when non-radiative processes are suppressed, made it possible to achieve such a significant improvement in reducing the threshold for observing SE in HgCdTe-based heterostructures. These studies once again confirm the prospects of heterostructures HgCdTe QWs as a material for interband lasers of the mid-IR range.
Acknowledgments
This work was financially supported by Russian Science Foundation (grant No. 22-12-00310).
[1] V. V. Rumyantsev et al., Opt. Eng. 60 (8), 082007 (2021).
[2] S. V. Morozov et al., ACS Photonics. 8 (12), 3526-3535 (2021).
[3] N. N. Mikhailov et al., Int. J. of Nanotechnology. 3 (1), 120 (2006).
