Impact of local strain from selective epitaxial germanium with thin Si/SiGe buffer on high-performance p-i-n photodetectors with a low thermal budget

This letter reports on the impact of selective epitaxial germanium, specifically its local strain effects, on highperformance p-i-n photodetectors for near-infrared applications. By combining a thin compliant Si epitaxial layer (∼6 nm) with SiGe buffer (10-15 nm), we demonstrated a high-quality Ge film (∼150 nm) prepared by two-step growth. Without using high-temperature cyclic anneal, Ge films with smooth surface (root mean square = ∼0.67 nm) and low dislocation density (4 × 10⁶ cm^-2) have been produced. The Si buffer locally enhances the tensile strain (e = 0.63%) in Ge while slightly suppressing the dark current by half to 0.12 μA (with circular ring area = 1230 μm² and spacing = 2 μm). A lateral p-i-n Ge photodetector has been demonstrated with enhanced photoresponse of ∼190 mA/W at 1520 nm and a 3-dB bandwidth of 5.2 GHz at 1 V.