Our group works in interdisciplinary topics in electrical engineering, applied physics, material science, and surface chemistry. Our graduate training places an emphasis on balancing hands-on engineering practices with fundamental studies in applied science. Technical areas we have worked on in the past decade include optoelectronic devices, power electronics, epitaxial growth, low dimensional nanostructures (nanowires, quantum dots), nanoscale characterization, and photonic physics. Students graduated from our group have found employment in industry, government laboratories, and academia.
MOCVD of AlGaInN for Solid State Lighting
Epitaxy of AlGaInN heterostructures and quantum wells remains one of the most critical issues in the realization of energy-efficient LEDs in general lighting applications. We are interested in means to enhance internal quantum efficiency and light extraction efficiency, and in understanding the interplay between material property and device performance.
Fundamental Issues of Crystal Growth
Crystal growth is the foundation science underpinning modern optoelectronic and microelectronic industry. The flexibility in contemporary epitaxial tools renders atomic-level precision in creating artificial structures, which in turn calls for a detailed understanding of kinetic and thermodynamic principles. We are interested in constructing a coherent and semi-empirical model describing mesoscopic processes such as island formation, coalescence, and surface morphology.
Monolithic Polychromatic Light Emitting Diodes
Monolithic integration of optical emitters with variable emission wavelengths opens us exciting opportunities in display, lighting, and sensing applications. The bandgap of InGaN ternary family spans from UV (3.4 eV) to IR (0.7 eV); light emission across the entire visible spectrum can be achieved by tuning the In composition. Here we explore the use of GaN micro-mesas prepared by selective area epitaxy. The presence of non-planar, multi-facetted mesas will support both intra-facet and inter-facet variation in indium incorporation, resulting in broad-band whitelight emission.
Nanotextured Medium for Photonic Applications
The goal of this project is to create a new class of semiconductor light-emitting medium with an enhanced radiation efficiency. We plan to demonstrate controlled, nanoscale
sculpting of a light-emitting semiconductor, in this case InGaN quantum well structures, into a strongly scattering medium, so that nanophotonic phenomena including photon localization and proximity resonance can be studied systematically. We plan to exploit the non-conventional lasing process with scattering-based feedback mechanisms toward broad-spectrum, high-efficiency lighting applications.
Quantum Dots for Quantum Electrodynamics
Due to their high exciton binding energies and slow surface recombination velocity, GaN quantum dots are attractive in realizing quantum-optical devices, such as single photon emitters and superradiance diodes at room temperature. Conventional approaches to GaN QDs are normally implemented on basal planes, which typically suffers a very high internal field (>6 MV/cm). Based on the knowledge in non-polar GaN growth, we are pursuing the fabrication of GaN quantum dots with Stransky-Krastanov nucleation on non-polar wafers.