title: Designer germanium quantum dot phototransistor for near infrared optical detection and amplification.
abstract: We demonstrated a unique CMOS approach for the production of a high-performance germanium (Ge) quantum dot (QD) metal-oxide-semiconductor phototransistor. In the darkness, low off-state leakage (Ioff ∼ 0.27 pA μm(-2)), a high on-off current ratio (Ion/Ioff ∼ 10(6)), and good switching behaviors (subthreshold swing of 175 mV/dec) were measured on our Ge-QD phototransistor at 300 K, indicating good hetero-interfacial quality of the Ge-on-Si. Illumination makes a significant enhancement in the drain current of Ge QD phototransistors when biased at both the on- and off-states, which is a great benefit from Ge QD-mediated photoconductive and photovoltaic effects. The measured photocurrent-to-dark-current ratio (Iphoto/Idark) and the photoresponsivities from the Ge QD phototransistor are as high as 4.1 × 10(6) and 1.7 A W(-1), respectively, under an incident power of 0.9 mW at 850 nm illumination. A superior external quantum efficiency of 240% and a very fast temporal response time of 1.4 ns suggest that our Ge QD MOS phototransistor offers great promise as optical switches and transducers for Si-based optical interconnects.
authors.affiliation: Department of Electrical Engineering and Center for Nano Science and Technology, National Central University, ChungLi, Taiwan, 32001, People's Republic of China.
authors.forename: M H
authors.initials: MH
authors.lastname: Kuo
authors.forename: W T
authors.initials: WT
authors.lastname: Lai
authors.forename: T M
authors.initials: TM
authors.lastname: Hsu
authors.forename: Y C
authors.initials: YC
authors.lastname: Chen
authors.forename: C W
authors.initials: CW
authors.lastname: Chang
authors.forename: W H
authors.initials: WH
authors.lastname: Chang
authors.forename: P W
authors.initials: PW
authors.lastname: Li