Our group focuses on the optical and electronic properties of epitaxially grown semiconductor heterostructures. We use molecular beam epitaxy to grow semiconductor crystalline layers with single atomic layer precision anywhere from a handful of atomic layers thick to many microns with purities better than one part in ten billion. Epitaxy also allows layering different lattice-matched or strained semiconductors.  Thick layered heterostructures with different bandgaps can be used to confine electrons, or light due to the differing indices of refraction.   Epitaxial growth allows realizing designer quantum structures, such as quantum wells, superlattices, quantum dots, and nanowires.  The remarkable control of material optical, electronic, and morphological characteristics has allowed the creation of important technologies, such as diode lasers, photodiode detectors, light emitting diodes, and photovoltaics spanning the electromagnetic spectrum, and high frequency transistors for fiber optic telecommunications, cell phones, solid state lighting, chemical sensing, solar cells, and a variety of other industrial and military technologies.  It has also stimulated much work on the fundamental physics of solids, been a playground for studying many basic quantum mechanical phenomena, and been the subject of several Nobel Prizes in Physics, including the fractional quantum Hall effect (1998), semiconductor heterostructures (2000), and solid state lighting (2014).  The 2018 Nobel Prize in Physics recognized the development of high energy, ultrafast pulses use chirped pulse amplification, a technology found in our tabletop ultrafast lasers, which we used to study semiconductor optical properties.

PDF iconThe Art and Science of Molecular Beam Epitaxy and the Nobel Prize for Blue LEDs.pd

Our current research focuses on:

  • Growth and properties of strained layer 6.1 Angstrom superlattices and alloys with short- to long-wave emission wavelengths, including vertical mobility, carrier recombination coefficients, micro- and atomic-scale defects, and phase stability.
  • High power, cascaded light-emitting diodes for optical chemical sensing of biomolecules in liquids, and thermal scene generation.
  • Growth, fabrication, and properties of semiconductor nanowire heterostructures.
  • Plasmonic structures for sub-wavelength optics for controlling and manipulating light
  • Purcell effect and photonic engineering for enhancing light-matter interaction in semiconductors

The facilities and techniques we use include:

  • Growth in the Molecular Beam Epitaxy Facility
  • Ultrafast optical spectroscopy, including time-resolved photoluminescence, and pump-probe spectroscopy
  • Semiconductor characterization techniques, such as light-current-voltage, C-V, and Hall measurements
  • Imaging techniques such as atomic force microscopy, scanning and transmission electron microscopy, and x-ray photoelectron spectroscopy at the Central Research Microscopy Facility.
  • Fabrication of micro- and nanostructures at the Microfabrication Facility.