PhD Defense: "Quantum Dot Lasers Epitaxially Grown on Silicon"

Alan Y. Liu

December 2nd (Friday), 2:00pm
Engineering Science Building (ESB), Room 1001

Silicon photonics is an emergent technology that leverages large area, low-cost silicon substrates and existing silicon microelectronics infrastructure for the low cost manufacturing of photonic integrated circuits on silicon. One of the key challenges for this technology has been the lack of a native silicon-based laser, due to the fact that silicon itself has an indirect band-gap. To circumvent inefficient light emission from silicon, current methods to fabricate silicon-based lasers typically rely on a separate material for the generation and amplification of light. These methods include integration of III-V materials onto silicon via wafer bonding or direct epitaxial growth, as well as band-gap engineering of group IV elements such as Ge or GexSn(1-x) grown on silicon for direct gap light emission.

Direct growth of efficient light emitting III-V materials onto silicon substrates is well suited for high-volume applications. Unfortunately, large dislocation densities typically result from the growth process due to fundamental material differences between III-V compound semiconductors and silicon, which are detrimental to laser performance and reliability. Recently, it has been shown that the utilization of three dimensional semiconductor quantum dots as the active region in III-V lasers grown on silicon can reduce non-radiative recombination at dislocations and result in efficient lasing operation. The reduced non-radiative recombination is a result of efficient capture and three-dimensional confinement of injected carriers by individual quantum dots. Furthermore, because individual dots are independent of each other, the effect of dislocations on the overall device performance is greatly diluted by the total number of dots, which can be made to be greater than the dislocation density.

In this talk, I will present research efforts in this area at the University of California, Santa Barbara. Starting with an overview of the materials growth process of semiconductor quantum dots by Molecular Beam Epitaxy, I will then review the performance of InAs/GaAs quantum dot lasers directly grown on silicon-based substrates as quantified by lasing threshold, output power, and maximum operating temperatures. Accelerated aging studies of the aforementioned devices will be presented, showing >20x improvement in device lifetime over previous GaAs based quantum well lasers grown on silicon. Finally, I will present measurements of the relative intensity noise of quantum dot lasers on silicon subjected to various levels of optical feedback, which suggests their potential for stable operation without the need for an optical isolator.

About Alan Y. Liu:

Photo of Liu Alan Y. Liu received his B.S. in Physics and Mathematics along with a minor in Business from Tulane University in 2011. He is currently working towards a Ph.D. degree in Electronic and Photonic Materials at the University of California Santa Barbara under the supervision of Professors John Bowers and Art Gossard. His research interests include III-V on silicon integration, quantum dot optoelectronics, and silicon photonics.

Hosted by: Professor John Bowers