A self-assembled microbonded germanium/silicon heterojunction photodiode for 25 Gb/s high-speed optical interconnects

Abstract

A novel technique using surface tension to locally bond germanium (Ge) on silicon (Si) is presented for fabricating high performance Ge/Si photodiodes. Surface tension is a cohesive force among liquid molecules that tends to bring contiguous objects in contact to maintain a minimum surface energy. We take advantage of this phenomenon to fabricate a heterojunction optoelectronic device where the lattice constants of joined semiconductors are different. A high-speed Ge/Si heterojunction waveguide photodiode is presented by microbonding a beam-shaped Ge, first grown by rapid-melt-growth (RMG) method, on top of a Si waveguide via surface tension. Excellent device performances such as an operating bandwidth of 17 GHz and a responsivity of 0.66 and 0.70 A/W at the reverse bias of −4 and −6 V, respectively, are demonstrated. This technique can be simply implemented via modern complementary metal-oxide-semiconductor (CMOS) fabrication technologies for integrating Ge on Si devices.

Silicon-plasmonic internal-photoemission detector for 40 Gbit/s data reception

“…In particular, a positive photocurrent of I p 38 μA is measured for an optical input power of 310 μW and a bias voltage of U 3.25 V. This corresponds to a sensitivity of S 0.12 A∕W, which is more than a factor of 6 higher than the sensitivity other IPE-based photodetectors [13,16]. Furthermore, the sensitivity is of the same order of magnitude as values typically measured for comparable state-of-the-art waveguide-based SiGe devices [18][19][20]. The steep increase of S I p ∕P for bias voltages φ bi < U < 1 V is caused by the fact that the transmission probability of electrons across the Ti-Si interface is sensitive to the distinct shape of the potential barrier.…”

“…Highest reported sensitivities amount to only 0.019 A/W at a wavelength of 1550 nm [16]more than 1 order of magnitude below those of state-of-the-art waveguide-integrated germanium PIN or avalanche photodiodes [18][19][20]. Moreover, the bandwidths of these devices are limited to 7 GHz by relatively long drift regions of more than 2 μm.…”

Rapid-melt-growth-based GeSi waveguide photodetectors and avalanche photodetectors

“…The dimensions of the vertical GeSi PIN and the lateral Si PIN are similar to those of the TT APD. Note that the vertical GeSi PIN, fabricated through SAMB Ge on Si, has been reported with low dark current at the order of μA at -6 V [6]. The i-Ge thickness is about 600 nm and the bonding temperature is as low as 400 o C. The lateral Si PIN is fabricated with Ni-silicide contacts [15], and features a low dark current of 100 nA at -6 V and a low breakdown voltage of 7.5 V. The measured dark currents of these three devices are summarized in Fig.…”

“…Such a method features low thermal budget and is fully compatible with CMOS fabrication process, but it doesn't seem feasible to make Ge and Si on the same plane for butt-coupling configuration. In the last section, we present the fabrication of a GeSi heterojunction PIN waveguide photodiode through RMG in combination with SAMB technique [6]. In that case, the optical signal is evanescentlycoupled from a SOI waveguide to a Ge absorber bonded on top of the Si rib.…”

High Efficient Ge Surface Absorption Through Hybridized Cavity and Horizontal Surface Plasmon Modes

“…Between the grating and the Ge substrate, a thin amorphous Si (5 nm) is inserted to passivate the Ge surface. Such an amorphous Si passivation technique is widely employed for Ge optoelectronic devices [14]. The normal light is TM polarized and the grating is made of Au.…”