Heterogeneous integration of InP etched facet lasers to silicon photonics by micro transfer printing

Photonics Integrated Circuits allow optical functionalities and interconnects with small footprint, large band -width and -density, low heat generation. The silicon photonics platform (SOI) offers excellent waveguiding properties, large-area wafers and a highly developed CMOS infrastructure matured with electronics. Nevertheless, the key function of light amplification is missing due to the indirect band-gap of silicon. The light has to be provided to the SOI from a separate direct band-gap III-V material. InP based devices work in the infrared optical window of the electromagnetic spectrum and can be heterogeneously integrated to the SOI. This research deals with the development of the first stand-alone InP Fabry-Perot lasers heterogeneously integrated to SOI by Micro Transfer Printing (µTP). The lasers are pre-fabricated and tested before transfer and are optimized to reach excellent optical, electrical and thermal performance. Lasers printed on Si substrates emit over 20 mW optical power, have threshold current of 16 mA and series resistance of 6 Ω; the thermal impedance of 38 K/W is half of that for the same laser printed directly on the SOI. The transfer printable InP ridge lasers have been designed as rectangular coupons with both contacts at the top and etched facets at the sidewalls. Two main release technologies based on the FeCl3:H2O (1:2) solution and a InGaAs or a InAlAs sacrificial layer were developed for releasing the devices from the original InP substrate with selectivity to InP greater than 4000 at 1 ◦C. The working principle of a polymer anchor system which restrains the devices to the substrate during the undercut were determined. The devices were printed on different silicon photonic substrates with excellent adhesion, with and without adhesive layers. A process for creating recesses into the SOI was developed to allow edge coupling the laser waveguide to the SOI or a polymer waveguide. High alignment accuracy along the three spatial directions can be achieved with alignment markers, reference walls and the interposition of a metal layer beneath the devices. This work shows a possible path for the achievement of a laser source for silicon photonics and it has been the basis for the integration of others InP devices to PICs by micro transfer printing

Transfer print techniques for heterogeneous integration of photonic components

The essential functionality of photonic and electronic devices is contained in thin surface layers leaving the substrate often to play primarily a mechanical role. Layer transfer of optimised devices or materials and their heterogeneous integration is thus a very attractive strategy to realise high performance, low-cost circuits for a wide variety of new applications. Additionally, new device configurations can be achieved that could not otherwise be realised. A range of layer transfer methods have been developed over the years including epitaxial lift-off and wafer bonding with substrate removal. Recently, a new technique called transfer printing has been introduced which allows manipulation of small and thin materials along with devices on a massively parallel scale with micron scale placement accuracies to a wide choice of substrates such as silicon, glass, ceramic, metal and polymer. Thus, the co-integration of electronics with photonic devices made from compound semiconductors, silicon, polymer and new 2D materials is now achievable in a practical and scalable method. This is leading to exciting possibilities in microassembly. We review some of the recent developments in layer transfer and particularly the use of the transfer print technology for enabling active photonic devices on rigid and flexible foreign substrates

Transferred III-V materials - novel devices and integration

Separating the substrate allows thin layers of III-V photonic semiconductor materials and devices to be integrated on foreign templates using transfer-printing. We demonstrate advanced light emitting and detecting devices based on this principle

Transfer printing of AlGaInAs/InP etched facet lasers to Si substrates

InP-etched facet ridge lasers emitting in the optical C-band are heterogeneously integrated on Si substrates by microtransfer printing for the first time. 500 μm × 60 μm laser coupons are fabricated with a highly dense pitch on the native InP substrate. The laser epitaxial structure contains a 1-μm-thick InGaAs sacrificial layer. A resist anchoring system is used to restrain the devices while they are released by selectively etching the InGaAs layer with FeCl3:H2O (1:2) at 8 °C. Efficient thermal sinking is achieved by evaporating Ti-Au on the Si target substrate and annealing the printed devices at 300 °C. This integration strategy is particularly relevant for lasers being butt coupled to polymer or silicon-on-insulator (SOI) waveguides

Microtransfer printing high-efficiency GaAs photovoltaic cells onto silicon for wireless power applications

Here, the development of high‐efficiency microscale gallium arsenide (GaAs) laser power converters, and their successful transfer printing onto silicon substrates is reported, presenting a unique, high power, low‐cost, and integrated power supply solution for implantable electronics, autonomous systems, and Internet of Things (IoT) applications. 300 µm diameter single‐junction GaAs laser power converters are presented and the transfer printing of these devices to silicon is successfully demonstrated using a polydimethylsiloxane stamp, achieving optical power conversion efficiencies of 49% and 48% under 35 and 71 W cm−2 808 nm laser illumination respectively. The transferred devices are coated with indium tin oxide (ITO) to increase current spreading and are shown to be capable of handling very high short‐circuit current densities up to 70 A cm−2 under 141 W cm−2 illumination intensity (≈1400 Suns), while their open circuit voltage reaches 1235 mV, exceeding the values of pretransfer devices indicating the presence of photon recycling. These optical power sources could deliver Watts of power to sensors and systems in locations where wired power is not an option, while using a massively parallel, scalable, and low‐cost fabrication method for the integration of dissimilar materials and devices

Comparison of InGaAs and InAlAs sacrificial layers for release of InP-based devices

Heterogeneous integration of InP devices to Si substrates by adhesive-less micro transfer printing requires flat surfaces for optimum attachment and thermal sinking. InGaAs and InAlAs sacrificial layers are compared for the selective undercut of InP coupons by FeCl3:H2O (1:2). InAlAs offers isotropic etches and superior selectivity (> 4,000) to InP when compared with InGaAs. A 500 nm thick InAlAs sacrificial layer allows the release of wide coupons with a surface roughness < 2 nm and a flatness < 20 nm. The InAlAs release technology is applied to the transfer printing of a pre-fabricated InP laser to a Si substrate

Edge-Coupling of O-Band InP Etched-Facet Lasers to Polymer Waveguides on SOI by Micro-Transfer-Printing

O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a 1.54~\mu \text{m} deep recess created in the 3~\mu \text{m} thick oxide layer of a 220 nm SOI wafer. A 7\times 1.5\,\,\mu \text{m}^{2} cross-section, 2 mm long multimode polymer waveguide was aligned to the ridge post-integration by e-beam lithography with \u3c 0.7~\mu \text{m} lateral misalignment and incorporated a tapered silicon waveguide. A 170 nm thick metal layer positioned at the bottom of the recess adjusts the vertical alignment of the laser and serves as a thermal via to sink the heat to the Si substrate. This strategy shows a roadmap for active polymer waveguide-based photonic integrated circuits