| dc.description.abstract | This thesis produced high-quality and single-crystal Ge quantum dots (QDs) using selectively oxidation of SiGe pillars, and demonstrated Ge-QD P-I-N near-infrared photodetectors with various sizes of Ge QD. The P-I-N photodetectors exhibit various near-infrared photoresponsivities by tuning different sizes of Ge-QD arrays integrated in the photodetectors. Under 2.5 mW illumination at 850, 980, 1310, and 1570 nm, the photodetectors exhibit the photo-current-to-dark-current ratio as high as 28, 15, 2.3, and 1.6, respectively. Under near-infrared illumination, the positive holes confined in the valance band offset between Ge QD and the Si substrate, establishing a built-in electric field (E-field), leading the transient response of the photodetectors as high as 440 MHz.
The other topic of this thesis focused the formation of near-infrared photodetectors with a 1-μm-thick Ge QD/Si heterojunction contained various number of Ge QD/Si stacks by using Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD), and investigated the photoresponsivity of the photodetectors affected by the number of Ge QD/Si stacks. The photo-current-to-dark-current ratio of the photodetectors is 4000 (0.45 mW), 2200 (0.45 mW), 52 (9.4 mW), and 4.2 (5.4 mW) under illumination at 850, 980, 1310, and 1570 nm, respectively. The open-circuit voltage increases with the number of heterojunction of Ge QD/Si, which indicates the increasing built-in E-field improves the photoresponsivity. | en_US |