Background ：
III-V PhC lasers with small footprint and low power consumption are potential ultra-compact and power-efficient light sources for future on-chip optical interconnects. Current fabrication of PhC lasers typically based on conventional vertical epitaxy, inevitably resulting in two major issues. Firstly, it struggles to form high-refractive-index-contrast structures, necessitating substrate undercut or transfer technic to form PhC membranes, which significantly increases fabrication complexity and compromises the mechanical stability of the devices. Secondly, the resulting horizontal QW layers spans the entire cavity plane, with all etched air holes penetrated the active region, leading to substantial ineffective pumping areas and additional surface non-radiative recombination, which severely limit pumping efficiency. Although techniques such as bonding and regrowth can address these challenges, these solutions based on vertical epitaxy generally require complicated and incompatible processing steps, resulting in high costs and poor scalability for mass production. Moreover, conventional PhC lasers are mainly fabricated using III-V substrates or heterogeneous bonding, with few demonstrations of direct monolithic integration via heteroepitaxy.
Highlights ：
The research team led by Yu Han and Siyuan Yu from Sun Yat-sen University has demonstrated monolithically integrated III-V membrane PhC lasers on SOI using innovative approach of selective lateral heteroepitaxy, achieving low-threshold single-mode lasing in the telecom band. Key highlights of the work include:
1. Monolithic integration of III-V PhC lasers :
By performing selective lateral heteroepitaxy on commercial SOI templates within a metalorganic chemical vapor deposition (MOCVD) system, the team achieved large-area growth of high-quality InP membranes, which are coplanar with the Si waveguide layer. The resulting InP membranes is sandwiched between silicon oxide layers, enabling strong optical confinement without the need for forming suspended structures, thereby significantly improving mechanical stability. The III-V material and Si layer share the same plane and thickness, facilitating highly efficient optical coupling between both devices and waveguides.
2. Precise control of the active region :
During the lateral growth of the InP membranes, vertical InGaAs/InP QWs can be precisely positioned at any desired location within the membranes, allowing precise alignment with the optical field maximum of the laser cavity. Moreover, the vertical QWs occupy only a small portion of the planar membrane area, avoiding etched air holes through the active region, which significantly reduces surface non-radiative recombination and thereby enhances pumping efficiency.
3. Simplified fabrication:
Selective lateral heteroepitaxy enables fabrication of PhC lasers with single growth step, eliminating the need for forming suspended structures, transfer technic, or doping processes. This reduction in process complexity facilities efficient, low-cost and full-wafer-scale production.
Summary and perspective ：
This study employs selective lateral heteroepitaxy to demonstrate the monolithic integration of III-V membrane PhC lasers on SOI. This platform demonstrates strong potential for realizing electrically pumped operation and efficient optical coupling with Si waveguides, offering a novel solution for the fabrication of PhC lasers. Furthermore, this technology is applicable to a variety of microcavity laser structures operating in different modes, including both horizontal edge-emitting and vertical surface-emitting configurations. This work marks an important step towards the application of electrically-pumped PhC lasers directly grown on SOI in the near future.
Light Science & Applications
Monolithic III–V membrane photonic crystal lasers on SOI using selective lateral heteroepitaxy