Optimizing SiGe–SiO2 Visible–Short-Wave Infrared Photoresponse by Modulating Interplay Between Strain and Defects Through Annealing

Abstract

SiGe-SiO₂-based structures present high interest for their high photosensitivity from visible to short-wavelength infrared. Herein, two postdeposition annealing procedures, that is, rapid thermal annealing (RTA) and rapid-like furnace annealing (FA), are compared. Both RTA and FA are performed at 600 °C for 1 min for SiGe nanocrystals (NCs) formation in SiO₂ matrix in Si/SiO₂/SiGe/SiO₂ structures deposited by magnetron sputtering. The FA imitates RTA resulting in enhanced spectral response. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy are carried out showing Ge-rich SiGe NCs with 11.3 ± 1.2 nm size for RTA and 9.4 ± 0.8 nm for FA. Photocurrent spectra for both structures show several peaks that are annealing dependent. The photocurrent intensity for FA samples is ≈7 times higher than RTA samples while cutoff wavelengths are slightly different, that is, 1365 nm for FA and 1375 nm for RTA. The FA structures show (at −1.5 V) over 4 A W⁻¹ responsivity at 730 nm, 6.4 × 10⁷ Jones detectivity at 735 nm, and 2.2 × 10⁷ Jones at about 1210 nm. FA structures contain small SiGe NCs with incorporated residual strain, while RTA ones are formed of columnar SiGe NCs separated by SiGeO_x amorphous regions and show increased tensile strain in the SiGe.