Silicon photonics is an optical analogue of silicon microelectronics. This area provides leading technological solutions for applications of integrated photonics, such as high performance computing and optical communications. In recognition of the high priority of silicon photonics, the DARPA microelectronics technology office made a major investment in 1.55-μm silicon photonics with its project on electronic and photonic integrated circuits (EPIC) in silicon. Optical signals are now well established as a means for efficient data transfer over a variable range of distances, from very long (like in the Internet) to very short (e.g., for inter-device communication). The current trend in silicon photonics is directed towards higher levels of integration and application in on-chip communications, which requires nanoscale optical sources. To circumvent inefficient light emission from silicon, current design of laser sources utilizes gain from materials popular in laser diode technology, mostly III-V semiconductor compounds. High level of integration involves direct growth of the nanostructured material with high gain - Quantum Wells (QWs) and Quantum Dots (QDs) –on the silicon substrates. Unfortunately, crystal lattice mismatch between III-V semiconductors and silicon may result in structure defects, which are detrimental to laser performance and reliability. In this regard, QDs, due to a smaller interface surface with the silicon substrate, seem to be more preferable than QW structures.
To confirm this idea, Liu et al. show that QD lasers are more reliable laser sources in comparison with QW lasers currently used in silicon photonics. The authors of this article review various approaches to integrate InAs/GaAs QD lasers for silicon photonics applications, focusing on direct epitaxial growth, and clearly demonstrate the advantage of using quantum dot active regions - high temperature, high power and low threshold operation. They conclude that QD based nanolasers directly grown on silicon are an interesting candidate as a scalable, low SWaP (size, weight, and power) light source for future short-reach silicon photonic interconnects.
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