Mid‐Infrared Intersubband Transitions in p ‐Type SiGe Parabolic Quantum Wells

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Abstract
The design, fabrication, and comprehensive characterization of hole‐doped Ge‐rich SiGe parabolic quantum wells engineered to exhibit intersubband transitions in the mid‐infrared spectral range around 120 meV are reported. The heterostructures are grown on Si substrates by low‐energy plasma‐enhanced chemical vapor deposition, enabling finely controlled compositional profiles and high crystalline quality. Thorough structural analysis confirms the formation of parabolic potential wells despite the presence of entropic interdiffusion. Photoreflectance spectroscopy is employed to investigate interband optical transitions in these heterostructures, whereas intersubband transitions are studied by Fourier‐transform infrared spectroscopy that revealed characteristic constant‐energy TM‐polarized absorption features up to room temperature. At higher doping levels, a more structured spectral response is observed due to valence‐band non‐parabolicity. Tight‐binding band structure simulations, incorporating many‐body effects, accurately reproduce the observed spectral features. These results highlight the potential of SiGe parabolic quantum wells as a versatile and scalable platform for the development of Si‐compatible mid‐infrared optoelectronic devices based on intersubband transitions.

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