Silicon Photonics: Lasers Grown Directly on Silicon Wafers
Why in the news
Researchers from the US and Europe reported, in Nature, a way to grow working lasers right on silicon wafers, tackling a long-standing hurdle for light-based chips.
About silicon and silicon photonics
- Silicon is a tetravalent metalloid, less reactive than carbon, and the second most abundant element in Earth’s crust (25.7% by weight, after oxygen). Pure silicon does not occur naturally.
- Silicon photonics uses silicon to build photonic integrated circuits (PICs) for fast data transfer and optical communication, made with standard CMOS processes.
- It uses photons instead of electrons, offering more speed and better energy efficiency; uses include data centres, sensors and quantum computing.
The problem
- Silicon has an indirect bandgap, so it cannot give out light efficiently; a laser source has to be integrated.
- External lasers attached today are slower, less efficient and costlier.
The breakthrough
- First demonstration of monolithic (fully integrated) lasers on a 300-mm silicon wafer, using CMOS-compatible steps suitable for existing fabrication lines.
- Nanoscale trenches trap material defects, an approach inspired by a 2007 study.
| Layer / parameter | Detail |
|---|---|
| Gallium arsenide (GaAs) | In trenches, traps defects |
| Indium gallium arsenide (InGaAs) | Emits light |
| Indium gallium phosphide | Protective cap |
| Drive current | 5 mA |
| Output power | About 1 milliwatt |
| Wavelength | 1,020 nm (short-range chip-to-chip links) |
| Lasers per wafer | 300 functional |
Reliability and limits
- Ran continuously for 500 hours at 25°C.
- Efficiency falls at 55°C, while industry wants steady working up to 120°C; thermal stability is the next challenge.
Significance
- Better performance and lower energy use for data centres and computers, with improved bandwidth and faster chip interconnects.
- A scalable, low-cost route to pair lasers with standard silicon chips.
Exam angle
- Technology: silicon photonics (light instead of electrons).
- Wafer size: 300 mm; wavelength: 1,020 nm.
- Key term: indirect bandgap.