Terahertz quantum cascade laser considering compositional interdiffusion effect

Wang, Li; Lin, Tsung‐Tse; Chen, Mingxi; Wang, Ke; Hasegawa, Hideki

doi:10.35848/1882-0786/acc568

Cited by 6 publications

(3 citation statements)

References 34 publications

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“…A direct comparison with other growth methods reported in the literature is difficult because of differences in crystallographic orientation, interfacial roughness, measurement methodology, probed interfacial area size, and growth conditions. Nevertheless, it is instructive to mention that state-of-the-art VS-grown GaAs/Al x Ga 1– x As(001) thin-film heterostructures (including quantum cascade laser structures) with x in the range of 0.3–0.4 exhibit interfacial widths of 3–4 ML, , which is among the sharpest binary/ternary alloy interfaces quoted in the literature. Impressively, our pulsed VLS growth mode resulted in comparable or even sharper axial interfaces in nanowires, highlighting the importance and the prospects of our findings.…”

Section: Resultsmentioning

confidence: 99%

At the Limit of Interfacial Sharpness in Nanowire Axial Heterostructures

Hilliard,

Tauchnitz,

Hübner

et al. 2024

ACS Nano

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As semiconductor devices approach dimensions at the atomic scale, controlling the compositional grading across heterointerfaces becomes paramount. Particularly in nanowire axial heterostructures, which are promising for a broad spectrum of nanotechnology applications, the achievement of sharp heterointerfaces has been challenging owing to peculiarities of the commonly used vapor−liquid−solid growth mode. Here, the grading of Al across GaAs/Al x Ga 1−x As/GaAs heterostructures in self-catalyzed nanowires is studied, aiming at finding the limits of the interfacial sharpness for this technologically versatile material system. A pulsed growth mode ensures precise control of the growth mechanisms even at low temperatures, while a semiempirical thermodynamic model is derived to fit the experimental Al-content profiles and quantitatively describe the dependences of the interfacial sharpness on the growth temperature, the nanowire radius, and the Al content. Finally, symmetrical Al profiles with interfacial widths of 2−3 atomic planes, at the limit of the measurement accuracy, are obtained, outperforming even equivalent thin-film heterostructures. The proposed method enables the development of advanced heterostructure schemes for a more effective utilization of the nanowire platform; moreover, it is considered expandable to other material systems and nanostructure types.

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Section: Resultsmentioning

confidence: 99%

At the Limit of Interfacial Sharpness in Nanowire Axial Heterostructures

Hilliard,

Tauchnitz,

Hübner

et al. 2024

ACS Nano

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“…We recently reported that neglecting interdiffusion during THz-QCL design can cause obvious discrepancies between the intended and actual wave functions layout. 24) The objective of this study is to provide a quantitative analysis of the impact of interdiffusion scattering on the self-consistent optical gain in THz-QCLs.…”

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confidence: 99%

“…28) By using APT, it can evaluate several interdiffusion parameters from the buried interfaces, i.e., the parameter of interdiffusion width L, which can be determined by fitting the one-dimensional composition profiles with an error function 29) or a sigmodal function. 30) In our MBE-grown GaAs/Al 0.3 Ga 0.7 As quantum structures, a three monolayers (MLs) interdiffusion width is assumed; 24) parameter of rms, which can be obtained from the reconstruction of the buried interfaces at each z(x, y) surface. Meanwhile, APT can also be used to estimate the out-plane (z axes) correlation length, labeled as Λ ┴ .…”

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confidence: 99%

Interdiffusion limiting on self-consistent optical gain in terahertz quantum cascade lasers

Wang¹,

Chen²,

Lin³

et al. 2023

Appl. Phys. Express

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In this study, the physical picture of imperfect interfaces is characterized by two terms of in-plane roughness and out-plane interdiffusion. The corresponding scattering is quantified using the nonequilibrium Green’s function model by setting an additional self-energy, and then the impact of scattering strength on GaAs/Al0.3Ga0.7As 2-well terahertz quantum cascade laser performance is investigated. It shows that the interdiffusion scattering term can lead to a maximum reduction of approximately 30% in self-consistent optical gain at a temperature of 300 K. The decrease of population inversion, rather than the broadening linewidth of radiation transition, is the primary factor contributing to the gain degradation. By excluding the effect of band structure deformation caused by interdiffusion in advance, the main cause for the reduction in population inversion is identified as the decoherence of resonant-tunneling injection resulting from interdiffusion scattering.

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Effects of background doping, interdiffusion and layer thickness fluctuation on the transport characteristics of THz quantum cascade lasers

Stanojević,

Demić,

Vuković

et al. 2024

Sci Rep

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In this work, we investigate the effects of n and p-type background doping, interface composition diffusion (interdiffusion) of the barrier material and layer thickness variation during molecular beam epitaxy (MBE) growth on transport characteristics of terahertz-frequency quantum cascade lasers (THz QCLs). We analysed four exemplary structures: a bound-to-continuum design, hybrid design, LO-phonon design and a two-well high-temperature performance LO-phonon design. The exemplary bound-to-continuum design has shown to be the most sensitive to the background doping as it stops lasing for concentrations around $$1.0\cdot 10^{15}$$ 1.0 · 10 15 –$$2.0\cdot 10^{15}$$ 2.0 · 10 15 cm$$^{-3}$$ - 3 . The LO-phonon design is the most sensitive to growth fluctuations during MBE and this is critical for novel LO-phonon structures optimised for high-temperature performance. We predict that interdiffusion mostly affects current density for designs with narrow barrier layers and higher $$\textrm{Al}$$ Al composition. We show that layer thickness variation leads to significant changes in material gain and current density, and in some cases to the growth of nonfunctional devices. These effects serve as a beacon of fundamental calibration steps required for successful realisation of THz QCLs.

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Terahertz quantum cascade laser considering compositional interdiffusion effect

Cited by 6 publications

References 34 publications

At the Limit of Interfacial Sharpness in Nanowire Axial Heterostructures

At the Limit of Interfacial Sharpness in Nanowire Axial Heterostructures

Interdiffusion limiting on self-consistent optical gain in terahertz quantum cascade lasers

Effects of background doping, interdiffusion and layer thickness fluctuation on the transport characteristics of THz quantum cascade lasers

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