Si-CMOS Compatible Photonics Integrated Circuits Platform

Strategy & Focus

• Components device/process module library
  
  IME has established a full suite of passives components library based SOI nanowires and SiN waveguides. With the optimised etch and side treatment techniques, our SOI waveguide loss matches well to the best reported by others, and the low-temperature, low-hydrogen content SiN waveguide exhibits much reduced loss at 1520nm.  With the addition of active photonic devices design and realisation, this project is one step closer to the final goal of achieving monolithic integration of all electronic and photonic devices in a single chip.

• Active components in modulator and photodetector
  
  The performance of selective epitaxial Ge (400nm)-on-SOI P-I-N mesa-type normal-incidence photodiodes using ~14nm low-temperature Si0.8Ge0.2 buffer without cyclic annealing. At -1V, very low bulk dark current densities of 1.5~2mA/cm2 were obtained indicating good material quality, and the peripheral surface leakage current densities were 14~19.5µA/cm. For 28µm-diameter round photodiode, the highest achieved external quantum efficiencies at -5V were 27%, 9%, and 2.9% for 850nm, 1.3µm, and 1.56µm optical wavelengths, respectively. 15×15µm2 square photodiode has 3dB bandwidth ≥15GHz at -1V. Good performance was achieved without high-temperature anneal, suggesting easy integration of Ge/Si-photodiode unto existing CMOS process. This work was published in Applied Physics Letters (2007) and presented in the International Conference on Group IV Photonics (2007).

• Local Strain Engineering
  
  Combining a thin compliant Si epitaxial layer (~6nm) with SiGe buffer (10-15nm), we demonstrated a high quality Ge-film (~150nm) prepared by two-step growth. Without using high-temperature cyclic anneal, Ge films with smooth surface (rms ~0.67nm) and low dislocation density (4×10 6 cm-²) have been achieved. The Si buffer locally enhances the tensile-strain (e = 0.63%) in Ge while slightly suppressing the dark current by half to 0.12 mA (circular ring area = 120 mm2 and spacing = 2mm). Lateral p-i-n Ge photo-detector has been demonstrated with enhanced photo-response of ~190mA/W at 1520 nm and 3-dB bandwidth of 5.2 GHz at 1V. This work has been accepted for publication in IEEE Electronics Device Letters (2007), and presented in the International Conference on Group IV Photonics (2007).
  
  The realisation of the passive and active devices building block equips this programme to work closer towards the ultimate goal of monolithic integration of full Si-photonics circuits. Such potential is expected to benefit the whole communication industry to expand their markets with cost-effective and high bandwidth communication products, such as HDMI for chasis-to-chasis connections through optical fibres.

Significant Results

Monolithically Integrated Ge-Photodetector on Si-CMOS compatible Photonics Platform

In the field of Si photonics, which processes and transmits information through photons instead of electrons, Ge photodetector on Si has been achieved monolithically. The device structure involves selective formation Ge epitaxial film (low defect ~106 cm -2) on Si, without invoking high-temperature anneal step which is traditionally performed. The achieved dark current (~8.6mA/cm2) is lower than the best published results available. This is accomplished through an innovative buffer-engineering. This low thermal budget integration scheme is friendlier than most other reported, since it eliminates the need of reengineering of the existing Si-electronics/photonics device technology platforms for CMOS IC driver/amplifiers as well as the photonics active phase-shifter. Meanwhile, the photodetector exhibits high-detecting speed of 15GHz. This work was presented in the International Conference on Group IV Photonics (2007).

Schematic diagram of cross-section of vertical incidence Ge/SiGe/Si P-I-N photodiode	Temporal impulse response of round (ф=10µm), and square-mesa (15µmx15µm) photodiodes at λ=1500nm, at reversed bias of 1V.

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