The responsivity and the bandwidth are both key parameters of a PD but also encounter tradeoff during the device designing due to the thickness of InGaAs layer absorbing light. In this paper, a balanced structure to achieve both high speed and relatively high responsivity is reported. A uni-traveling carrier PD(UTC-PD) structure is taking advantage of the high drift velocity to meet the rather high-speed exhibition. For responsivity enhancing, we apply back reflector beneath the top-illuminated UTC-PD based on micro transfer printing. To further increase the bandwidth of small size PD, we optimize the shape of CPW electrodes of PDs. With our final structure, the UTC-PD exhibits 3dB bandwidth of 100GHz and responsivity of 0.4A/W.
A silicon hybrid photodetector was demonstrated based on die-to-die bonding technology. The vertically incident InGaAs/InP photodetector die was integrated on silicon-on-insulator (SOI) die by using divinyldisiloxane benzocyclobutene (DVS-BCB) as adhesive layer. A grating coupler was fabricated on SOI substrate to diffract the light out of the SOI waveguide into the detector. The measured coupling efficiency output at 1550 nm for the TE mode reached to 39.8%, which is equal to 8.2 dB fiber-to-fiber loss. After integrating, when the thickness of the BCB bonding layer was 380 nm, the optical loss reached to 13.8 dB with 30×30 μm2 device. The measured dark current, bandwidth and responsivity of the hybrid InGaAs/InP photodetector with light absorbing mesa of 10×10 μm2 were 37.7 nA, 30.9 GHz and 0.48 A/W respectively at -3 V DC bias.
We experimentally demonstrate high-speed InGaAs/InP drift-enhanced photodetectors with different diameters and absorbing layer thicknesses. For photodiodes with optical window diameters of 10 μm, 7 μm and 5 μm, we have achieved 3-dB bandwidths of 32GHz, 40 GHz and over 40 GHz from a 500-nm-thickness intrinsic InGaAs absorption layer and 30 GHz, 34 GHz and 36 GHz bandwidths from a 700-nm-thickness absorption layer, respectively. The measured values are in good agreement with the theoretical calculations.
A heterogeneous photonic integration of silicon photonic devices and III-V compound semiconductor photodetector (PD) is demonstrated by micro transfer printing (μ-TP). Via transfer printing, InP/InGaAs PIN PD is directly bonded on the top of silicon grating coupler by ultra-thin DVS-BCB adhesion layer. 0.4A/W of photo-responsibility @1550nm and ~25GHz of -3dB bandwidth are measured on printed PD. No deterioration in coupling loss is detected in the printed PD on the silicon gratings coupler with alignment accuracy of ±1μm. This technique enables a feasible route to photonic integrated circuits.
We have demonstrated a class of drift-enhanced InGaAs/InP p-i-n photodetectors with the top-illuminated light in the 1550 nm wavelength band. An InGaAsP layer is used at the InGaAs/InP hetero-interface to reduce the contact resistivity. For devices of 10 μm × 10 μm, 20 μm × 20 μm and 30 μm × 30 μm mesa areas, the 3-dB bandwidths are measured to be 32 GHz, 12 GHz and 6 GHz, respectively. Also we have obtained a dark current of 64 nA and a responsivity of 0.43 A/W at -4 V bias for 10 μm × 10 μm photodetector.
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