Abstract
We perform a detailed comparison of 2D Auger coefficients in narrow-gap type-I and type-II quantum wells (T1QWs and T2QWs), and the relative effects of Auger non-radiative decay on midwave infrared lasers employing both types of gain media. Comparison is also made to 3D Auger coefficients in bulk mid-IR materials, by defining a “normalization length” that accounts for the spatial extent of the electron and hole wavefunctions in the quantum wells. The comparisons confirm that Auger recombination in both types of QW is substantially suppressed relative to bulk, due primarily to the effects of compressive strain on the valence subband dispersions. We find that the 2D Auger coefficients in T1QWs remain substantially lower than those in T2QWs out to wavelengths beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5~\mu \text{m}$ </tex-math></inline-formula> . However, this does not necessarily imply a lower lasing threshold because a substantial fraction of the holes injected into T1QWs occupy lower subbands that do not contribute gain, so more must be injected to reach the lasing threshold. When all of the relevant considerations are combined, the thresholds for the best T1QW and T2QW lasers cross over near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda ~\approx ~3.0~\mu \text{m}$ </tex-math></inline-formula> . Other characteristics governing the relative T1QW and T2QW laser performances above threshold, such as maximum output power and wallplug efficiency, are also considered.
Highlights
O NGOING advances in semiconductor laser and detector technologies for the midwave infrared have substantially expanded their use in systems addressing such commercial and military applications as chemical sensing [1]–[3], infrared countermeasures [4], and thermal imaging [5], [6]
We find that the net thresholds for T2QWs remain lower for wavelengths down to at least ≈ 3.1 μm, this still fails to tell the whole story as will be discussed
We have clarified and quantified the physical mechanisms determining threshold current and power densities in narrow-gap type-I and type-II QW lasers, which are emerging as central components in a new generation of compact mid-IR optoelectronic systems
Summary
O NGOING advances in semiconductor laser and detector technologies for the midwave infrared (mid-IR, loosely defined here as 2-6 μm) have substantially expanded their use in systems addressing such commercial and military applications as chemical sensing [1]–[3], infrared countermeasures [4], and thermal imaging [5], [6]. For interband lasers operating in the mid-IR, threshold current densities are nearly always limited by the non-radiative Auger process, in which electron-hole recombination is accompanied by the excitation of a third carrier (either electron or hole) to an excited state that conserves energy and momentum [7], [8]. Auger recombination can affect the laser damping factor, optical feedback dynamics [9], and dark current in mid-IR photodetectors, it is less likely to dominate in detectors since they typically operate at very low optical excitation levels, and often at cryogenic temperatures to maximize the detection sensitivity. Previous studies have analyzed and characterized the effects of Auger recombination on specific types of mid-IR lasers and detectors [10]–[19]. We will show that the Auger coefficient alone does not reliably predict which QW configuration minimizes the threshold current density, or overall laser performance
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