Waveguided Ge/Si Phototransistor With High Responsivity

The low-bias phototransistors featured with high responsivity have been widely applied in optoelectronic detection and optical communications. However, the conventional phototransistors are typically with large dark current, degrading the performance severely. In this work, we propose a new Ge/Si-based phototransistor formed by a N/P/i-Ge/N structure. Within the structure, an intrinsic Ge serves as the absorption region and the Base region is p-type doped on silicon. Experimentally, we demonstrate up to 102.81 A/W responsivity at the wavelength of 1550 nm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.60 \; \mu $ </tex-math></inline-formula>A dark current, with the applied bias voltage of 1 V. To our knowledge, this is 2x improvement in responsivity compared to the reported phototransistors. Moreover, the excess noise power spectral density is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.29 \times 10^{-{20}}$ </tex-math></inline-formula> W/Hz. The device has exhibited remarkable improvements in photocurrent and optical response.