| dc.description.abstract | This thesis focuses on the application of Germanium quantum dots (QDs) phototransistor for the near infrared photodetection and amplification. The main characteristics of the Ge QD phototransistor is based on the framed structure of typical metal-oxide-semiconductor field-effect transistor (MOSFET), incorporating 50 nm Ge QDs embedded in gate dielectrics. The heterostructures of 50 nm Ge QDs/SiO2/Si were formed using the selective oxidation of poly-SiGe pillar, incorporating Ge QDs array into the gate dielectrics of MOSFET, which is a compatible approach with prevailing CMOS technologies.
In the darkness, the Ge QDs phototransistors exhibit low off-state leakage (IOFF ~0.27 pA/μm2), high on-off current ratio (ION/IOFF ~106), and good switching behavior (subthreshold slope = 195 mV/dec), indicating a good hetero-interfacial quality of Ge-on-Si due to a 4-5 nm-thick interfacial SiO2 layer between Ge and Si. Additionally, under 0.9 mW illumination at 850 nm, the Ge QDs phototransistors exhibit significant photo-current-to-dark-current ratio and high photoresponsivity as high as 6×106/0.67 A/W at off-state (VG = -5 V), and 64/2.7 A/W at on-state (VG = 4 V), respectively, indicating the strong absorption of Ge QDs. These results offer a great promise for future Si-based optical interconnection applications. Moreover, the temperature-dependent measurement was conducted from 300 to 77 K at the dark and under illumination in order to identify the mechanisms of photocurrent of Ge QDs phototransistors. As temperature decreasing, the photocurrent is invariant indicating the origin of the photoresponse is related to Ge QDs not the traps. The 3-dB bandwidth of Ge QDs phototransistors is ~410 MHz. | en_US |