High-performance Ge p-i-n APDs fabricated by point-defect healing

An international group has created low-defect germanium (Ge) p-i-n avalanche photodiodes (APDs) via a point-defect-healing process consisting of annealing between 600°C and 650°C. The APDs have a sub-1-μA dark current for reverse currents below 5 V, a low operating voltage (avalanche-breakdown voltage of 8 to 13 V), and a multiplication gain of 440 to 680. The researchers hail from Sungkyunkwan University (Suwon, South Korea), Stanford University (Palo Alto, CA), Samsung Electronics (Gyeonggi-Do, South Korea), Korea University (Seoul, South Korea), and Nanyang Technological University (Singapore).

A 1-μm-thick intrinsic Ge film was heteroepitaxially grown on a silicon (Si) substrate; next, a 15-nm-thick film of silicon dioxide (SiO₂) was grown as a deposition stop. Implanting boron and phosphorus then defined the p- and n-well regions; well depth was about 300 nm. Arsenic and boron ions were implanted next to form n+ and p+ regions, which had been previously photolithographically patterned. The point defects were healed by annealing in a nitrogen atmosphere for 1 hr, then the SiO₂ layer was removed by etching. Finally, titanium and aluminum films were deposited on the lithographically defined areas. Current/voltage (I/V) measurements were taken using a laser light source emitting 0.25 mW at a 1.3 μm wavelength. The optimum doping concentration of the p-type intrinsic region was on the order of 10¹⁷ cm^-3. Contact Jin-Hong Park at[email protected].