Low-Temperature Fabrication of Wafer-Bonded Ge/Si p-i-n Photodiodes by Layer Exfoliation and Nanosecond-Pulse Laser Annealing

Abstract

We report a potential method for the fabrication of Si-based Ge film with low threading dislocation (TD) density (<;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) based on a low-temperature Ge/Si wafer bonding and smart cut technique. This method may replace the traditional epitaxial growth to solve the problems related to the TDs, high temperature, and high vacuum. A near-bubble-free Ge/Si bonded interface is achieved for the fabrication of Ge/Si p-i-n photodiodes. The insertion of amorphous Ge (a-Ge) has crystallized after Ge layer exfoliation, achieving a small FWHM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">XRD</sub> (96 arcsec) of the Ge peak. This determines the low dark current density (5.97 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and low ideality factor (1.19) of the Ge/Si p-i-n photodiode. The exfoliated Ge film suffers from in-plane compression strain due to the expansion of the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas during the blistering process. Interestingly, the in-plane compression strain turns into tensile strain after high-temperature postannealing due to the faster shrinkage rate of Ge during cooling. The in-plane tensile strain leads to the increase in the responsivity of the photodiode. The responsivity of the photodiode at 1310 nm increases from 0.505 to 0.71 A/W and that at 1550 nm increases from 0.244 to 0.524 A/W after postannealing. More importantly, the redshift of the absorption edge of the Ge/Si photodiode (0.1 A/W at 1630 nm) is also observed. This implies that the wafer-bonded Ge/Si p-i-n photodiode can be comparable with the epitaxial one and can be used for optical communication in all wavelength division multiplexing bands, including the L-band (1565-1625 nm) and entire C-band (1530-1565 nm).