Researchers have developed monolithic integrated semiconductor lasers with silicon photonic circuits

Silicon (Si) photonics has recently become a key enabling technology for many applications, thanks to proven silicon process technologies, large wafer sizes, and silicon optical properties. However, silicon-based materials do not emit light efficiently, requiring the use of other semiconductors as light sources. Iii-v semiconductors, i.e. materials made from groups III and V elements of the periodic table, are the most efficient semiconductor laser sources. For decades, their monolithic integration on silicon photonic integrated circuits (PIC) has been considered a major challenge in achieving fully integrated, dense silicon photonic chips. Despite recent advances, only discrete III-V lasers grown on bare silicon wafers have been reported to date, regardless of wavelength and laser technology.

In a new paper published in the journal Optical Science and Applications, a team of European scientists from France, Italy, and Ireland, led by Professor Eric Tournie from the University of Montpellier, France, has now unlocked a semiconductor laser with an efficient integrated chip of silicon photonics and optical coupling into passive photonic devices.

Their approach relies on three pillars: Si-PIC design and fabrication, III-V material deposition, and laser fabrication. To perform this proof-of-concept, PIC is made from a transparent S-shaped SiN waveguide embedded in a SIO-2 matrix. The SiO 2 /SiN/SiO 2 stack is etched away in the depressed area to open the Si window for deposition of III-V material. It is essential to maintain a high crystal quality on the silicon surface after etching. GaSb technology was chosen as the III-V material because it can emit over the entire mid-infrared wavelength range, where many gases have fingerprint absorption lines. Molecular beam epitaxy (MBE) is a technique that operates under ultra-high vacuum and is used to grow semiconductor layer stacks. Scientists have previously demonstrated that this technique can eliminate special defects that typically occur at the Si/III-V interface and cause device failures. In addition, the MBE can precisely align the laser portion of the emitted light with the SiN waveguide.

Finally, diode lasers are fabricated from epitaxial layer stacks by microelectronic process. At this stage, high quality mirrors must be manufactured by plasma etching to enable laser emission. Despite the complexity of the process, the performance of these integrated diode lasers is similar to that of diode lasers grown on a native GaSb substrate. In addition, the laser is coupled to the waveguide, and the coupling efficiency accords with the theoretical calculation.

The scientists summarized the work:

"The different challenges presented by the special architecture of the final device (PIC fabrication and patternization, regrowth on the patterned PIC, laser processing of etched surfaces in the recessed regions, etc.) were overcome to demonstrate that laser emission and light coupling into passive waveguides with coupling efficiency in line with theoretical calculations."

"Although demonstrated by a mid-infrared diode laser for gas sensing applications, this approach can be applied to any semiconductor material system. In addition, it can be scaled to any silicon wafer size with a diameter of at least 300 mm and provides an epitaxial reactor."

"The reported methods and techniques will open up new avenues for future silicon photonic integrated circuits. They solve a long-standing problem and lay the foundation for future low-cost, large-scale, fully integrated photonic chips."

Source: Laser Network