Cerutti, L

Gassenq, Alban

Hattasan, Nannicha

Kuyken, Bart

Rodriguez, JB

Roelkens, Günther

Tournié, E

Van Thourhout, Dries

Ghent University Academic Bibliography

Heterogeneously integrated InGaAsSb detectors on SOI waveguide circuits for shortN. Hattasan1, A. Gassenq1, B. Kuyken1Photonics Research Group, 2 Université Montpellier 2 Author e Abstract: We present evanescently couplon silicon-on-insulator waveguide circuits for shortresponsivity of 0.13 A/W is obtained at a wavelength of 3.5 µA at -1V. OCIS codes: (130.0130) Integrated optics 1. Introduction While silicon photonics is an important platform technology for applications in the telecommunicationband, the use of silicon photonics in other wavelength ranges has been neglected so far. However, many applications could benefit from a silicon photonic integrated circuit for wavelengths outside the telecommunication wavelength range. Especially, towards longer wavelengths (2platform for integrated spectroscopic solutions, in which a shortwhich contains strong and very substancewaveguide circuits are very appealing to realize such a spectroscopic function, given the transparency of the waveguide circuit in that wavelength range and the available knowspectrometers on this platform using CMOS fabrication technology. In order to realize such an integrated spectroscopic system, the dense integration of shortmonolithically integrated Ge photodetectors are response cuts off at around 1.6µm. In order to extend the wavelength range, the heterogeneous integration of IIIsemiconductor photodetectors is required. There are two approaches to extend the opetowards longer wavelengths. One approach is to use ternary InGaAs absorption layers grown on an InP substrate. While the cut-off wavelength of lattice matched InGaAs is only 1.7µmcan be done by using lattice-mismatched “extended” InGaAs, which allows reaching the 2.5µm wavelength range. However, in this work, we focus on an alternative approach, which relies on quaternary InGaAsSb absorbing layersin a p-i-n layer stack, grown lattice mcan be heterogeneously integrated on and coupled to a siliconbonding technique based on DVS-BCB bonding. Experimentally, we obtaA/W at a wavelength of 2.17µm, with a dark current of  2. Device design The photodetectors are thin-film pDVS-BCB adhesive layer.  (a)                       Figure 1. a) Cross-section of an evanescently coupled InGaAsSb photodetector based on BCB bonding; b) influence of the InGaAsSb absorbing layer thickness on the absorbed power fraction in a 50um long-wave infrared applications 1, L. Cerutti2, J.B. Rodriguez2, E. Tournié2, Roelkens1 Ghent University - imec, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium– CNRS, UMR 5214, Place Bataillon, 34095 Montpellier, France-mail address: nannicha.hattasan@intec.ugent.be ed, heterogeneously integrated InGaAsSb photodetectors -wave infrared applications. A fiber2.17µm. The photodetector ; (130.3120) Integrated optics devices -3.5µm), silicon photonic circuits could become the dominant -wave infrared broadband beam probes an analyte-specific absorption bands in this wavelength range-how on how to realize compact integrated -wave infrared compatible photodetectors is required. While key components for the telecommunication wavelength range, their  [2], further probing the shortatched on a GaSb substrate. We will show that these photodetector structures -on-insulator waveguide circuit, using an adhesive in a fiber-to-detector 3.5 µA at -1V. -i-n photodetectors integrated on top of the silicon waveguide circuit using a                                                                        (b)   D. Van Thourhout1, G.   -to-detector dark current is  wavelength   [1]. Silicon photonic -V rational wavelength range -wave infrared  responsivity of 0.13    PD  BCB 45 nm  The interfacing between the silicon waveguide and the InGaAsSb pcoupling. A cross-section of the envisaged structure is shown in figure 1a. structure is realized which allows power transfer between the two waveguide layers. photodetector epitaxy stack thickness is required to realize an optimally compact photodetector, since the most efficient power transfer occurs when phase matching is achieved between the silicon waveguide mode and a guided mode in the III-V epitaxial layer stack. This is shown in figure 1b, showing the absorbed power fraction for a given detector stack (50µm long) as a function of 3. Device fabrication The silicon waveguide circuits used waveguide losses of a single mode waveguide characterized by a cut-back measuremelayer, an intrinsic InGaAsSb absorbing layer, a pGaSb substrate using MBE [3]. While originally the capsemiconductor surface, this prevented good bonding due to the hydrophilic nature of the IIIof the cap-layer. Therefore, this layer was incorporated in the photodetector layer stack. V epi-stack onto the silicon waveguide circuit, a diepolymer bonding agent [4]. By diluting the DVSbonding layer thicknesses down to 60nm were successfully realized. After bonding the IIIdown onto the silicon waveguide circuit, the GaSb substrate is removed using a combination of mechanical grinding and wet chemical etching using a HF:CrOepitaxial films were obtained this way. After epitaxial layer transfer, photodetectors are processed, lithographically aligned to the underlying SOI waveguide circuit, as shown in figure 2a. combination of wet (Citric acid: H2Othe resulting device. A cross-section of a fabricated photodetector is shown in figure 2b, clearly shundercut due to the wet chemical etching of the mesa.                                                                  Figure 2. a) Schematic representation of process flow for the InGaAsSb photodetectors; b) focused ion beam crossimage of the fabricated devices ; c) top4. Device characterization  The devices were characterized at room temperature. The setup consists of a midcoupled to standard SMF. After polarization control, thhotodetector is realized using evanescent In this way a vertical directional coupler the intrinsic absorbing layer thickness and BCB bonding layer thickness.consist of a 220nm silicon waveguide layer on a 2µm buried oxide layer. The in the 2-2.5µm wavelength range are in the range of 3dB/cmnt. The photodetector layer stack consists of an n-doped GaSb contact layer and an InAsSb cap layer, grown on a -layer was to be removed prior to bonding, to get a clean In order -to-wafer bonding process is applied, using DVS-BCB using mesitylene, bonding of GaSb3 solution, until an InAsSb etch stop layer is reached. High quality The mesa definition is realized using a 2:H3PO4:H2O) and dry etching (CH4:H2) in order to optimize the dark current of  The mesa is 9µm wide.                  (a)  (b)                                      (c) -view of the fabricated photodetectors on top of a silicon waveguide circuit -infrared tunable laser that is e light is injected into the silicon waveguide circuit using P-contact P-contact n-contact 50 µm Optimization of the  , as -doped InAsSb cladding -V surface after removal to integrate the III--BCB as a -based epi-structures with -V die, epitaxial layers owing the  -section  diffractive grating couplers defined in the silicon waveguide layer. Preliminary characterization of the grating coupler showed a peak fiber coupling efficiency of -11dB at a wavelength of 2.17um for TE polarized light. Since the integrated photodetector is only 600µm away from the grating coupler, the loss in the silicon entrance waveguide (due to scattering losses and the BCB absorption loss) can be neglected. Figure 3a shows the obtained IV curves for the fabricated devices under illumination (at 2170nm). A low dark current of 3.5µA at room temperature can be observed. A fiber-to-chip responsivity of 0.13 A/W was realized, corresponding to an on-chip device responsivity of more than 1A/W. High responsivities were obtained up to 2.4µm. The linear response as a function of input power is shown in figure 3b. To our knowledge this is the first realization of an integrated photodetector capable of addressing the 2-2.5µm wavelength range.                                                       (a)                                                                                         (b)             Figure 3. a) IV characteristics of the fabricated photodetectors showing a low dark current and good responsivity; b) linearity of the photodetector response  5. Conclusions This paper describes the first realization of heterogeneously integrated InGaAsSb photodetectors on a silicon waveguide circuit. The device performance is very promising for the realization of integrated spectroscopic systems on silicon, provided that device arrays can be realized with good uniformity. Initial results, which will be discussed at the conference, show that this is the case. This opens many opportunities for the use of ultra-compact silicon-based spectroscopy systems, e.g. for the monitoring of glucose levels in blood samples or for gas sensing applications. The emerging field of non-linear optics beyond the two-photon absorption threshold in silicon [5], might also benefit from the availability of integrated photodetectors on the waveguide platform. Acknowledgements This work was partly carried out in the framework of the IWT-SBO-Glucosens project and the FP7-ERC-MIRACLE project. References   [1]  Crowder et al.,”Infrared methods for gas detection”, in Mid-infrared semiconductor optoelectronics, Springer (2006)  [2] J. Brouckaert, G. Roelkens, D. Van Thourhout, R. Baets, Compact InAlAs/InGaAs Metal-Semiconductor-Metal Photodetectors Integrated on Silicon-on-Insulator Waveguides,IEEE Photonics Technology Letters, 19(19), p.1484-1486 (2007)   [3] E. Tournié and A. Trampert, “MBE growth and interface formation of compound semiconductor heterostructures for optoelectronics,” Phys. Stat. Sol. (b) 244 (8), 2683-2696 (2007)  [4] G. Roelkens, J. Brouckaert, D. Van Thourhout, R. Baets, R. Notzel, M. Smit, Adhesive Bonding of InP/InGaAsP Dies to Processed Silicon-on-Insulator Wafers using DVS-bis-Benzocyclobutene,Journal of Electrochemical Society, 153(12), p.G1015-G1019 (2006)  [5] X. Liu, R.M. Osgood, Y. Vlasov, and W. Green, “Mid-infrared optical parametric amplifier using silicon nanophotonic waveguides”, Nature Photonics 4, 557-560 (2010) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0-400-2000200400600800  Current (µA)Voltage (V) 0mW 0.8mW 1.1mW 1.6mW 2.2mw 3.3mW -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5-500-400-300-200-1000  Photo Current (µA)Fiber Input Power (mW) 

Heterogeneously integrated InGaAsSb detectors on SOI waveguide circuits for short-wave infrared applications

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Heterogeneously integrated InGaAsSb detectors on SOI waveguide circuits for short-wave infrared applications

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