Making Low-Cost, High-Performance Silicon Photonics a Reality with Quantum Dot Lasers
Quantum dot lasers on silicon
The largest challenge in low-cost silicon photonics has been developing lasers by epitaxial growth on silicon substrates without sacrificing performance. Building upon Prof. Kroemer’s research on epitaxial growth on silicon 30 years ago, UC Santa Barbara researchers have demonstrated that this goal is within reach.
Facilitated by a collaboration between Prof. John Bowers and Prof. Art Gossard, researchers at UC Santa Barbara have combined existing expertise in both materials growth using Molecular Beam Epitaxy (MBE) and photonics to overcome this challenge. They have created telecom-wavelength quantum dot lasers by epitaxial growth on silicon substrates with record performance characteristics among lasers on silicon. This is the first time UC Santa Barbara researchers have produced quantum dot lasers on silicon by epitaxial growth.
Quantum dots are very small particles of semiconducting material measuring a few nanometers tall and tens ofnanometers across (you could fit 50 billion of them on the face of a penny). Each dot emits light independently of the others. This unique property makes quantum dot lasers robust and less sensitive to crystallographic imperfections compared to traditional “quantum well” laser designs.
Background on explosive data growth
According to IBM, 90% of the world’s data was generated over the last two years. With the continued proliferation of mobile devices, cloud computing, and the internet itself, explosive growth in data generation is unlikely to slow down anytime soon. Transferring this sheer volume of data currently accounts for approximately 5% of total U.S. power consumption, and is projected to rise to 10% in a few years. Growing data demands also put a strain on existing infrastructure; network providers must find ways to increase bandwidths to accommodate increasing data traffic.
Challenges of low-cost photonics
Solutions to the two largest challenges associated with data growth — the need to reduce power consumption and increase bandwidth of data transfers — can be simultaneously achieved by using photonics to transmit information in the form of light. Unfortunately, high costs have limited the use of photonics to relatively long distance data transmission, and cheaper copper links are more common today for short-distance transmission. One way to increase the cost-competitiveness of photonic data transmission is to fabricate components on silicon wafers in existing silicon foundries — so-called “silicon photonics.”
One complication to this approach is finding a suitable light source compatible with silicon as a host material. Since silicon itself is an inefficient light emitter, the laser has to be made from a different material such as III-V compound semiconductors. The most economic approach is to make the laser from these III-V semiconductors grown on silicon substrates. However, this growth process results in a high density of crystallographic imperfections due to fundamental material differences between silicon and III-Vs, which in the past resulted in poor laser performance.
As networks scale to higher bandwidths to accommodate growing data traffic, copper links will become less and less feasible. Since today’s copper link data transmission technologies experience signal attenuation at higher data rates, replacing them with low-cost silicon photonics will greatly facilitate and expedite our transition toward energy-efficient data communication.
 “Big Data, for Better or Worse: 90% of World’s Data Generated Over Last Two Years.” Science Daily, May 22nd, 2013.
 A. Y. Liu, C. Zhang, J. Norman, A. Snyder, D. Lubyshev, J. M. Fastenau, A. W. K. Liu, A. C. Gossard, and J. E. Bowers, “High performance continuous wave 1.3 μm quantum dot lasers on silicon.” Applied Physics Letters 104 (2014)
Author: Alan Y. Liu, January 2014
Materials Department, UC Santa Barbara
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Authors and publication details:
A. Y. Liu, C. Zhang, J. Norman, A. Snyder, D. Lubyshev, J. M. Fastenau, A. W. K. Liu, A. C. Gossard, and J. E. Bowers, “High Performance Continuous Wave 1.3 μm Quantum Dot Lasers on Silicon.” Applied Physics Letters 104 (2014).