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- ItemSubnanometer Control of the Heteroepitaxial Growth of Multimicrometer-Thick Ge /(Si, Ge) Quantum Cascade Structures(College Park, Md. [u.a.] : American Physical Society, 2023) Talamas Simola, Enrico; Montanari, Michele; Corley-Wiciak, Cedric; Di Gaspare, Luciana; Persichetti, Luca; Zöllner, Marvin H.; Schubert, Markus A.; Venanzi, Tommaso; Trouche, Marina Cagnon; Ortolani, Michele; Mattioli, Francesco; Sfuncia, Gianfranco; Nicotra, Giuseppe; Capellini, Giovanni; Virgilio, Michele; De Seta, MonicaThe fabrication of complex low-dimensional quantum devices requires the control of the heteroepitaxial growth at the subnanometer scale. This is particularly challenging when the total thickness of stacked layers of device-active material becomes extremely large and exceeds the multi-μm limit, as in the case of quantum cascade structures. Here, we use the ultrahigh-vacuum chemical vapor deposition technique for the growth of multi-μm-thick stacks of high Ge content strain-balanced Ge/SiGe tunneling heterostructures on Si substrates, designed to serve as the active material in a THz quantum cascade laser. By combining thorough structural investigation with THz spectroscopy absorption experiments and numerical simulations we show that the optimized deposition process can produce state-of-the-art threading dislocation density, ultrasharp interfaces, control of dopant atom position at the nanoscale, and reproducibility within 1% of the layer thickness and composition within the whole multilayer. We show that by using ultrahigh-vacuum chemical vapor deposition one achieves simultaneously a control of the epitaxy down to the sub-nm scale typical of the molecular beam epitaxy, and the high growth rate and technological relevance of chemical vapor deposition. Thus, this technique is a key enabler for the deposition of integrated THz devices and other complex quantum structures based on the Ge/SiGe material system.