Oxygen-partial-pressure modulation of the near-infrared photoresponse in reactively sputtered SiO2/Ge-nanocrystal/SiO2/p-Si heterostructures

Silicon-compatible near-infrared photosensitive heterostructures are attractive for integrated optoelectronics, but in group-IV nanocrystal (NC) structures on crystalline silicon, a spectral maximum near the Si absorption edge cannot be assigned to the nanocrystals from wavelength alone. Here, oxygen partial pressure (OPP) during reactive radio frequency sputtering is treated as a process variable that modulates the steady-state photoresponse of coupled SiO2/Ge-nanocrystal/SiO2/p-Si heterostructures. Stacks containing a nominal 4.7 nm Ge interlayer were grown at 400 °C using 25%–75% OPP. The revised analysis combines OPP-dependent spectral photoresponse, dark/illuminated current-voltage characteristics, a process-matched Ge-free oxide control at OPP75, wavelength-dependent incident-power calibration, and a layer-resolved transfer-matrix/effective-medium model constrained by previously published morphology. Across the Ge-containing series, the response maximum spans approximately 1014–1130 nm with an overall redshift and narrowing, although the intermediate-OPP values are nonmonotonic. The matched oxide-only control shows a broader substrate-edge-like response and does not reproduce the narrow high-amplitude band of OPP75EG47 near 1130 nm, demonstrating an additional contribution associated with the Ge-containing interlayer/interfaces without implying that Ge-NCs are the dominant absorber. A representative device remains strongly nonideal (ideality factor about 2.1; series resistance about 75 kΩ). Conservative optical bounds show that the Ge-NC:SiO2 region absorbs less than approximately 2% of incident power at the measured maxima, whereas the Si substrate absorbs roughly 7%–81%. The NIR response is, therefore, best described as substrate-assisted and overlayer-modulated. The contribution of this work is a process-structure-photoresponse attribution framework rather than a performance-optimized photodetector.