Comprehensive Study on Chip-Integrated Germanium Pin Photodetectors for Energy-Efficient Silicon Interconnects

Abstract

Optical interconnects are promising alternatives to copper-based wirings in on-chip communications. Recent advances in integrated group-IV nanophotonics should address a range of challenges related with speed, energy consumption and cost. Monolithically integrated germanium pin photodetectors on silicon-on-insulator (SOI) waveguides are indispensable devices in this buoyant research field. Here, we comprehensively investigate the opto-electrical properties of hetero-structured pin photodetectors. All photodetectors were fabricated on top of 200mm SOI substrates using industrial-scale semiconductor manufacturing processes. Under a low-bias voltage supply of 1 V, pin photodetectors exhibit dark-currents from 5 nA to 100 nA, dark current densities from 0.404 A/cm 2 to 0.808 A/cm 2 , responsivities in a range of 0.17 A/W to 1.16 A/W, and cut-off frequencies from 7 GHz to 35 GHz, respectively. Such achievements make them promising for use in power-efficient optical links operating at 40 Gbps, with a device energy dissipation of only few fJ per bit. Index Terms-Complementary metal-oxide-semiconductor technology, germanium photodetectors, inter-and intra-chip interconnects, optical communications, silicon nanophotonics.

28 Gbps silicon-germanium hetero-structure avalanche photodetectors

“…The fabricated devices were fully characterized in laboratories of Centre de Nanosciences et de Nanotechnologies through static current-voltage measurements, small-signal radio-frequency testing, and large-signal data link measurements for eye diagram acquisitions and bit-error-rate assessments, respectively. A detailed description of the manufacturing flow and the comprehensive opto-electrical characterization techniques used on devices can be found elsewhere [35][36][37] .…”

“…The dark-currents measured in Si-Ge-Si photodetectors are comparable to others hetero-junction devices 29,30 and considerably lower than in devices with pure Ge junctions 17,19,20,22,24,26,28 . The darkcurrent increases with the reverse bias (for a fixed device geometry) and becomes higher when the intrinsic region is less wide (for a fixed bias) 37 . Small-footprint diodes are desired and preferred, as they facilitate low noise operation, i.e.…”

“…Various types of waveguide-integrated optical photodetectors with a p-i-n structure have been studied the last 10 to 15 years. Since the first fabrication of waveguide-integrated diodes by Ahn, et al 19 , a large number of homo-junction (full Ge structures) [15][16][17][18][19][20][21][22][23][24][25][26][27][28] and hetero-junction (combined Si-Ge structures) [29][30][31][32][33][34][35][36][37] devices have been proposed, fabricated and experimentally evaluated. Both types of devices make use of p-i-n junctions, with light absorption in the intrinsic zones.…”

“…It otherwise yields, because of optical index confinement differences between Ge and Si, a much better light confinement in the intrinsic device zone, significantly improving photodetector performances. Hetero-structured Si-Ge photodetectors have already been demonstrated with significantly better performance metrics across the near-infrared (near-IR) fiber-optic communication wavelengths [31][32][33][34][35][36][37] .…”

Silicon chip-integrated fiber couplers with sub-decibel loss

“…For Si nanophotonics, silicon-on-insulator (SOI) substrates have been established as prominent and widely accessible material platforms for many applications, markets, and end-users [1][2][3] . Although pure SOI platforms, with Si as a waveguide core, definitely lacks active on-chip functionalities [4][5][6][7][8] , the fundamental passive function of light guiding is their key advantage 9,10 . Moreover, dense integration ability, low-cost fabrication, high-yield production within Sifoundry-compatible environment are other advantages offered by SOIs.…”