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 (I-off similar to 0.27 pA mu m(-2)), a high on-off current ratio (I-on/I-off similar to 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 (I-photo/I-dark) and the photoresponsivities from the Ge QD phototransistor are as high as 4.1 x 10(6) and 1.7 AW(-1), respectively, under an incident power of 0.9mW 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.