B.S., 2005, University of Virginia
Ph.D., 2010, Massachusetts Institute of Technology
Postdoctoral Scholar, Stanford University
Quantum Dot Opto-electronics
When the dimensions of a material are limited to the nanoscale, quantum confinement can dramatically alter properties relative to the bulk material. For colloidal quantum dots (QD), controlling the particle size allows us to create bright, wavelength tuneable emitters and absorbers spanning the infrared, visible and ultraviolet regions. The use of QDs in novel opto-electronic devices and solar cells is pursued by developing an all-inorganic system consisting of QDs embedded in a semiconductor matrix. Research focuses on both understanding the electronic properties of QD based devices and applying QDs for novel optical applications in the visible and infrared spectrum.
For many earth abundant materials, such as lead sulfide, the band gap of the bulk material is too small to be useful in harvesting solar energy because most of the energy absorbed is lost to heat. These same materials, in QD from, can be matched perfectly to the solar spectrum. Alternately, the emission properties of QDs can be used for advanced detection and emission applications such as multispectral imagers and light emitting devices.
Fabrication of QD Enhanced Devices
A combination of solution-phase and gas-phase chemistry techniques are used to fabricate all-inorganic systems with high carrier mobility for opto-electronic applications. By encapsulating the QDs in an inorganic matrix, the QD surface can be efficiently passivated and a low tunneling barrier between QDs maintained. We pursue encapsulation by atomic layer deposition, which is a highly conformal, industrial technique for depositing thin films of a wide variety of semiconductors.
Infrared absorbing PbS QDs
Characterization of QD Devices
Every combination of QD and inorganic matrix presents a unique opto-electronic system. Defects at the QD surface or within the inorganic matrix can dramatically affect conduction, making understanding the electronic and structural properties essential for developing high efficiency devices. The mobility and carrier density are explored using techniques such as field effect mobility measurements and temperature dependent conductivity. The physical properties are characterized by techniques such as x-ray diffraction and x-ray photoelectron spectroscopy.
Field effect transistor geometry