Designer germanium quantum dot phototransistor for near infrared optical detection and amplification

• Published in: Nanotechnology 2015-02, Vol.26 (5), p.055203-055203
• Main Authors: Kuo, M H, Lai, W T, Hsu, T M, Chen, Y C, Chang, C W, Chang, W H, Li, P W
• Format: Article
• Language: English
• Subjects: Darkness; Germanium; germanium quantum dots; Illumination; MOS phototransistor; Nanotechnology; optical interconnect; Optical interconnects; Phototransistors; Quantum dots; Quantum efficiency; Swing; Transducers
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/0957-4484/26/5/055203

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 m−2), a high on-off current ratio (Ion Ioff ∼ 106), 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 × 106 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.