InP membrane directly modulated semiconductor lasers (DMLs) with photon-photon resonance (PPR) have a lot of potential to be used in short-range telecommunication systems due to their small footprint, high energy efficiency, and high modulation bandwidth. However, the stability of the S21 response in PPR-based devices is sensitive to precise phase-matching between the lasing mode and PPR mode. We designed, fabricated, measured, and analyzed a C-band DML with active phase-tuning achieved by a thermal phase shifter on top of a long passive waveguide. The phase shifter enables tuning of the PPR frequency in the range of 5 GHz resulting in the PPR peak power enhancement of 16 dB. We study the small-signal responses at different combinations of bias current and phase shifter current and show, that in some cases the phase shifter enables a bandwidth that cannot be achieved by sweeping the bias current. The laser dynamic behavior is simulated and the influence of the most important design and processing parameters on bandwidth is studied in detail.

Wafer bonding is a key process in heterogeneous photonic integration and benzocyclobutene (BCB) is widely used for adhesive wafer-to-wafer bonding when it comes to handling complex topography on both wafers. However, until now a major drawback of bonding with BCB was the high thermal impedance of lasers due to the low thermal conductivity of BCB. We demonstrate, that by optimizing the membrane device topography and introducing the BCB reflow step into the process flow it is possible to achieve full planarization of 1 μm topography at the wafer scale while ensuring only 135 nm of BCB between the laser p-contact and the substrate. We show experimentally, that the thermal impedance of 500 μm long distributed feedback (DFB) laser was reduced from 585 to 271 K W⁻¹ when bonded to Si substrate, and to 174 K W⁻¹ when bonded to SiC substrate using the new method.

The fast-maturing photonic integration technology is calling for a versatile platform that supports both active and passive functions as well as high scalability through component miniaturization. Indium phosphide (InP) has long been recognized for its ability to deliver a comprehensive suite of photonic components. InP membrane technology has emerged as a next-generation solution that could unite the functional completeness with high scalability. This paper describes recent advancements in the InP-membrane-on-Si (IMOS) platform, which supports high-performance passives, polarization and mode handling, native light sources, amplifiers, modulators and detectors, and novel material integration.

Heterogeneous integration helps to maximize the performance of photonics or electronics devices by leveraging the strengths of diverse material platforms within a unified process flow. A promising approach is the 3D integration of InP photonic or electronic membranes to other substrate materials containing photonics or electronics ICs via adhesive bonding. However, wafer-scale spatial distortions arising from the bonding process can compromise fabrication. Herein, we used electron-beam metrology to investigate the distortion of InP membranes resulting from wafer-scale bonding with benzocyclobutene (BCB). We measured both the linear and residual components of distortions across the tested wafers. First, bonding of InP substrate with BCB on various carrier substrates (Si, InP, SiC, and glass) was realized, which unveiled post-bonding membrane expansion factors in the range of ~0-325 ppm and beyond that for the glass carrier. The diversion of these values from theoretical estimations was linked to the adhesive bonding process. Next, we examined the effect of BCB thickness in the ranges of 1-12μm, residual mechanical stress, and the impact of defects on distortions. Using these findings, we experimentally verified that the largest part of distortions can be efficiently pre-compensated to overcome the challenges of multilayer overlay errors in the fabrication of heterogeneously integrated photonic and electronic devices.

We demonstrated a sidewall-corrugated sampled grating fabricated on the InP membrane platform, achieving a 0.3 nm 3-dB bandwidth. Theoretically, a laser, using this type grating in an external cavity, can enable a <40 kHz linewidth and a 55 nm tuning range. © 2024 The Author(s)

Electron Beam Lithography (EBL) metrology and least-square estimation of wafer-scale distortions is used to determine InP membrane deformation as a result of bonding to different substrate materials. First, the accuracy of EBL as a metrology tool for this particular application was assessed. Next, modelling of distortions was tested on unbonded InP wafers as a reference for extracting post-bonding distortions. Then we investigated the effect of substrate material choice on InP membrane deformation after bonding. We found residual expansion factors of 4.53±1, 312.4±1, and 317±1 ppm of the InP membrane bonded to InP, Si, and 3C-SiC carriers, respectively. For the SiO2 carrier, the 3inch InP membrane split into smaller membranes to reduce the stress, highlighting the importance of substrate choice.