About

The research in our lab uses advanced data science techniques to understand how water, plants, geology and climate interact in a tightly coupled system – and how humans are changing this system.

Research topics

• Computer Science
• Nanotechnology
• Optoelectronics
• Materials science
• Optics
• Physics
• Engineering
• Electronic engineering
• Electrical engineering
• Geography
• Condensed matter physics
• Composite material
• Engineering physics

Selected publications

• List of contributors

  Elsevier eBooks · 2021

  • Computer Science
  • Computer Science
  • Geography
  PublisherDOI

• Reliability of lasers on silicon substrates for silicon photonics

  Elsevier eBooks · 2021 · 7 citations

  • Computer Science
  • Materials science
  • Optoelectronics
  PublisherDOI

• Recombination-enhanced dislocation climb in InAs quantum dot lasers on silicon

  Journal of Applied Physics · 2020 · 22 citations

  • Materials science
  • Condensed matter physics
  • Optoelectronics

  We analyze the structure of dislocations in electrically aged InAs quantum dot (QD) lasers on silicon to understand gradual device degradation. We find that misfit dislocations lengthen due to carrier injection, experiencing a combination of recombination-enhanced climb and glide processes constrained by the epitaxial structure. An examination of the dislocation geometry reveals that the climb process involves the addition of atoms to the extra half plane of the dislocation. Spontaneous emission from the QDs is also dimmer after aging. Additionally, the signature of misfit dislocations in the unaged laser, discernible as sharp dark lines in spatially resolved cathodoluminescence, is replaced by finer, more inhomogeneous contrast upon aging. We speculate that this change arises from vacancy clouds expelled from the dislocation during climb. With this insight, we evaluate the driving forces for dislocation climb that could be at play and discuss the origins of slow degradation in QD lasers.

  PublisherOA PDFDOI

• Analysis of the optical feedback dynamics in InAs/GaAs quantum dot lasers directly grown on silicon

  Journal of the Optical Society of America B · 2018-10-11 · 69 citations

  articleOpen accessCorresponding

  This work reports on a systematic investigation of the influence of optical feedback in InAs/GaAs quantum dot lasers epitaxially grown on silicon. The boundaries associated to the onset of the critical feedback level corresponding to the first Hopf bifurcation are extracted at different bias conditions with respect to the onset of the first excited state transition. Overall, results show that quantum dot lasers directly grown onto silicon are much more resistant to optical feedback than quantum well lasers, mostly resulting from a small linewidth enhancement factor of high-quality quantum dot material. However, results also unveil that the onset of the critical feedback level strongly depends on the excited-to-ground-state ratio, hence a figure of merit showing that a small ratio of the excited-to-ground-state lasing thresholds is not beneficial for maintaining a high degree of stability. This work brings further insights in the understanding of quantum dot laser physics and is useful for designing feedback resistant lasers for isolator-free transmission in metro, access, and data center optical networks, as well as for integrated photonics.

  PublisherOA PDFDOI

• Photonic Integration With Epitaxial III–V on Silicon

  IEEE Journal of Selected Topics in Quantum Electronics · 2018-07-09 · 149 citations

  article1st authorCorresponding

  We present a brief overview of the various leading platforms for photonic integration. Subsequently, we consider the possibility of a photonic integrated circuit platform utilizing epitaxially grown III-V material on silicon-without the need for wafer bonding, or an externally coupled laser. Finally, a techno-economic analysis contrasting the aforementioned platforms will be presented.

  PublisherDOI

• Wide Band-Gap Semiconductor Based Power Electronics for Energy Efficiency

  2018-03-13 · 20 citations

  reportOpen accessSenior author

  Recent advances in wide band-gap (WBG) semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN) are enabling a new generation of power semiconductor devices that far exceed the performance of silicon-based devices. Past ARPA-E programs (ADEPT, Solar ADEPT, and SWITCHES) have enabled innovations throughout the power electronics value chain, especially in the area of WBG semiconductors. The two recently launched programs by ARPA-E (CIRCUITS and PNDIODES) continue to investigate the use of WBG semiconductors in power electronics. From materials and devices to modules and circuits to application-ready systems integration, ARPA-E projects have demonstrated the potential of WBG semiconductors to lower the cost of high-efficiency power electronics to enable broad adoption in energy applications.

  PublisherOA PDFDOI

• InAs Quantum Dot Micro-disk Lasers Grown on (001) Si Emitting at Communication Wavelengths

  2017-01-01

  article

  Continuous-wave optically-pumped micro-disk lasers epitaxially grown on silicon with single mode lasing at communication wavelengths from liquid helium to room temperature is reported. Growth of the InAs quantum dots (QDs) gain medium was carried out on high crystalline quality GaAs/InP-on-silicon templates. Special defect filtering techniques have been employed to minimize the impact of the highly lattice-mismatched heteroepitaxial growth on (001) silicon substrates. Compared with quantum wells, the multi-stack InAs QDs are less sensitive to residual defects originated from the hetero-interfaces. Using QDs in a micro-disk resonant cavity with minimized non-radiative surface recombination leads to low-threshold lasing in the micro-disks with a few microns in diameter.

• Electrically pumped continuous-wave 13  μm quantum-dot lasers epitaxially grown on on-axis (001)  GaP/Si

  Optics Letters · 2017-01-10 · 150 citations

  articleOpen access1st authorCorresponding

  We demonstrate the first electrically pumped continuous-wave (CW) III–V semiconductor lasers epitaxially grown on on-axis (001) silicon substrates without offcut or germanium layers, using InAs/GaAs quantum dots as the active region and an intermediate GaP buffer between the silicon and device layers. Broad-area lasers with uncoated facets achieve room-temperature lasing with threshold current densities around 860  A/cm2 and 110 mW of single-facet output power for the same device. Ridge lasers designed for low threshold operations show maximum lasing temperatures up to 90°C and thresholds down to 30 mA.

  PublisherOA PDFDOI

• Electrically pumped continuous wave quantum dot lasers epitaxially grown on patterned, on-axis (001) Si

  Optics Express · 2017-02-14 · 119 citations

  articleOpen access

  High performance III-V lasers at datacom and telecom wavelengths on on-axis (001) Si are needed for scalable datacenter interconnect technologies. We demonstrate electrically injected quantum dot lasers grown on on-axis (001) Si patterned with {111} v-grooves lying in the [110] direction. No additional Ge buffers or substrate miscut was used. The active region consists of five InAs/InGaAs dot-in-a-well layers. We achieve continuous wave lasing with thresholds as low as 36 mA and operation up to 80°C.

  PublisherDOI

• Quantum dot lasers grown on (001) Si substrate for integration with amorphous Si waveguides

  Optical Fiber Communication Conference · 2017-01-01 · 5 citations

  article

  Heteroepitaxially grown InAs quantum dot lasers were demonstrated on (001) Si under continuous-wave optical pumping with low thresholds (down to 35 µW). The feasibility of integrating active and passive devices through electrical injection was analyzed.

  PublisherDOI

Frequent coauthors

• John E. Bowers

  38 shared

• A. C. Gossard

  University of California, Santa Barbara

  25 shared

• Qiang Li

  Cardiff University

  21 shared

• Kei May Lau

  University of Hong Kong

  21 shared

• Yating Wan

  King Abdullah University of Science and Technology

  20 shared

• Justin Norman

  University of California, Santa Barbara

  12 shared

• Evelyn L. Hu

  Harvard University

  11 shared

• Daehwan Jung

  Korea University of Science and Technology

  8 shared

Labs

• Alan Liu's LabPI

  Not provided

Awards & honors

• Making Visible the Invisible (permanent installation, 2005)
• John Simon Guggenheim Fellowship in Visual Arts (2016)
• Creative Capital Foundation support
• Daniel Langlois Foundation for the Arts, Science and Technol…
• National Endowment for the Arts support