64  Gb/s low-voltage waveguide SiGe avalanche photodiodes with distributed Bragg reflectors

Abstract

We demonstrate low-voltage waveguide silicon-germanium avalanche photodiodes (APDs) integrated with distributed Bragg reflectors (DBRs). The internal quantum efficiency is improved from 60% to 90% at 1550 nm assisted with DBRs while still achieving a 25 GHz bandwidth. A low breakdown voltage of 10 V and a gain bandwidth product of near 500 GHz are obtained. APDs with DBRs at a data rate of 64 Gb/s pulse amplitude modulation with four levels (PAM4) show a 30%–40% increase in optical modulation amplitude (OMA) compared to APDs with no DBR. A sensitivity of around − 13 dBm at a data rate of 64 Gb/s PAM4 and a bit error rate of 2.4 × 10 − 4 is realized for APDs with DBRs, which improves the sensitivity by ∼ 2 dB compared to APDs with no DBR.

Silicon–germanium receivers for short-wave-infrared optoelectronics and communications

“…SACM APDs advantageously combine the high absorption in Ge and the low multiplication noise of Si, yielding another degree of flexibility to engineer device performances. Most of the SACM structures use vertical diode architectures [154,156,159,[161][162][163][164][165][166]174] instead of lateral ones [172,176]. However, the vertical diode scheme calls upon more process steps, with dedicated epitaxy and metal contacting on Ge, which may degrade the overall performances.…”

“…However, the vertical diode scheme calls upon more process steps, with dedicated epitaxy and metal contacting on Ge, which may degrade the overall performances. Moreover, typical SACM APDs use a single voltage to control electric fields in those, by design, separated regions [161][162][163][164]. This, in turn, calls upon delicate charge layer optimization, i.e.…”

“…More recent works concentrated on APD structures, operating at low [160][161][162][163][164][165][166] or high [167,168,[173][174][175] voltages, fitting the needs of on-off keying (OOK) systems with direct detection at 25 and 28 Gbps. More specifically, Chen et al [160] demonstrated a 25 Gbps O-band receiver with vertical p-i-n APDs.…”

“…Improved capability of on-chip Si-Ge detectors has also been investigated using spectrally efficient multi-level formats such as 4-level pulse amplitude modulation (PAM-4) [163][164][165][177][178][179][180] rather than conventional OOK modulation [137, 144, 154, 157-162, 164, 166, 169-173, 176]. Verbist et al [177] obtained an APD with 40 Gbps and 50 Gbps PAM-4 detection through 42 and 10 km long transmission links.…”

“…However, power sensitivity was not quantified here. Huang et al [163,180] demonstrated a lowvoltage Si-Ge APD with distributed Bragg reflectors (DBRs). Indeed, optimized DBRs reflect the unabsorbed light back to the SACM APD, which in turn, substantially enhances the device quantum efficiency from 60 to 90%.…”