Hyper Self-Doping of GeIn for Cost-Effective Ge PIN Photodiodes with Record-Low Dark Current

In this study, cosputtering hyper self-doping germanium indium (GeIn) for construction of p-GeIn/i-Ge/n-Ge photodiodes in low-temperature processes is demonstrated with record-low dark current. The nonequilibrium epitaxial growth of GeIn at a low temperature effectively inhibits the lateral migration of indium, rendering uniform distribution of indium with a high concentration. The p-type doping concentration of GeIn films is up to 8 × 1020 cm–3, and the specific contact resistivity of Al/Ni/GeIn contact is as low as 3.5 × 10–8 Ω·cm2, which result in a large rectification ratio of 2 × 107 for the photodiode with an ultralow dark current of 0.54 nA@-1 V, corresponding to a dark current density of 0.028 mA/cm–2. The high responsivity of 0.45 A/W and the specific detectivity of 1.01 × 1011 Jones are achieved for the PIN photodiode at −1 V bias under illumination of 1550 nm. The groundbreaking results demonstrate that our novel cosputtering strategy for achieving a hyper-doped GeIn epitaxial layer overcomes the longstanding challenge of developing high-performance, cost-effective Ge-based optoelectronic devices compatible with low-temperature monolithic integration processes.