Room Temperature InP DFB Laser Array Directly Grown on (001) Silicon (1501.03025v1)

Abstract: Fully exploiting the silicon photonics platform requires a fundamentally new approach to realize high-performance laser sources that can be integrated directly using wafer-scale fabrication methods. Direct band gap III-V semiconductors allow efficient light generation but the large mismatch in lattice constant, thermal expansion and crystal polarity makes their epitaxial growth directly on silicon extremely complex. Here, using a selective area growth technique in confined regions, we surpass this fundamental limit and demonstrate an optically pumped InP-based distributed feedback (DFB) laser array grown on (001)-Silicon operating at room temperature and suitable for wavelength-division-multiplexing applications. The novel epitaxial technology suppresses threading dislocations and anti-phase boundaries to a less than 20nm thick layer not affecting the device performance. Using an in-plane laser cavity defined by standard top-down lithographic patterning together with a high yield and high uniformity provides scalability and a straightforward path towards cost-effective co-integration with photonic circuits and III-V FINFET logic.

• The paper introduces a novel MOVPE-based selective area growth to integrate InP DFB lasers on silicon, confining defects within a 20 nm region.
• It reports high-yield single-mode lasing at ~930.5 nm with precise wavelength tuning through grating design for dense WDM applications.
• The work offers a scalable, CMOS-compatible approach for integrating efficient lasers on silicon, enhancing photonic-electronic integration.

Monolithic Integration of InP DFB Lasers on Silicon: A Step Towards High-Volume Silicon Photonics

The research paper focuses on the realization of high-performance InP-based distributed feedback (DFB) lasers monolithically integrated onto silicon substrates using selective area growth (SAG) techniques, a critical challenge in the field of silicon photonics. Silicon, with its well-established manufacturing processes, offers an ideal platform for integrated photonic and electronic devices, yet lacks efficient native light-emitting sources due to its indirect bandgap. The incorporation of direct bandgap III-V semiconductors like InP addresses this limitation, although it introduces significant complexities arising from lattice and thermal mismatches. This paper details the innovative methods to overcome these challenges and demonstrates the functionality of InP lasers on a 300mm (001) silicon substrate at room temperature, suitable for wavelength-division multiplexing (WDM) applications.

Key Contributions

1. Innovative Epitaxial Growth Technique: The authors employ selective area metal-organic vapor-phase epitaxy (MOVPE) to grow InP in pre-defined trenches on silicon, carefully controlled to minimize defects typically induced by substantial lattice mismatch (~8% for InP/Si). This method confines dislocations and anti-phase boundaries within a 20 nm region, ensuring the integrity of the overlying III-V material and its optical properties.
2. High-Quality DFB Laser Array Fabrication: Using standard top-down lithography and a high-precision etching process, high-quality InP DFB lasers are fabricated, exhibiting single-mode lasing with emission centered around 930.5 nm. Notably, the approach leads to a high yield, with over 98% of devices demonstrating successful laser operation.
3. Wavelength Control and Scalability: By varying the grating period and phase shift within the DFB cavity design, the authors achieve fine control over the lasing wavelengths, crucial for enabling dense WDM systems. The demonstrated scalability is underlined by the uniform performance across a laser array tested with identical design parameters.
4. Enhancements in Optical Mode Alignment: The optical confinement within the diamond-shaped waveguide minimizes the overlap with defect regions, critical for preserving the modal gain and achieving low-threshold lasing action. Comprehensive analysis reveals that pumping efficiency and defect management at the interface play pivotal roles.

Implications and Future Directions

The methods demonstrated have profound implications for integrated photonic circuits. The monolithic integration of lasers on silicon substrates, absent of thick buffer layers, enhances compatibility with complementary metal-oxide-semiconductor (CMOS) processes, facilitating greater interaction between electronic and photonic components. This integration promises reduced costs and increased performance for optical interconnects, particularly beneficial for high-capacity data centers.

Significant future directions include the exploration of electrically injected devices and expansion into longer-wavelength operations to enhance compatibility with existing telecommunications infrastructure. The introduction of ternary or quaternary compounds could enable carrier confinement and wavelength red-shifting, enhancing device performance and expanding operational versatility. Further, the potential integration on silicon-on-insulator (SOI) platforms offers promising avenues for minimizing substrate loss and improving thermal management.

In summary, the authors provide a comprehensive demonstration of integrating efficient laser sources directly onto silicon using a scalable and CMOS-compatible process. The results present a substantial advancement towards embedding optical functionalities within silicon platforms, potentially opening pathways to a new paradigm of photonic-electronic integration.