Condensed Matter: Semiconductors: Optoelectronics
Cavity Ring-down Investigation of Distributed Bragg Reflectors (DBRs)
DBRs are semiconductor mirrors which are grown as an integral part of a device. They are used to create the optical cavity in vertical-cavity surface-emitting lasers (VCSELs). Cavity ring-down is an optical technique which is extremely sensitive to any sources of optical loss within the measurement cavity. The optical cavity was initially set up by Dan Utley '05 as part of his Senior I.S. project. During REU 2005, Danny Tremblay redesigned the cavity and achieved resonance. Ian Steward (REU 2007) successfully used the cavity to measure the reflectance of a DBR after modifying the cavity to allow measurement of the light from the front end of the cavity (instead of the back of the cavity) to minimize the effects of scattering from the back mirror. Henry Timmers (Senior IS '09) is working on another redesign to incorporate optical feedback and make the cavity more stable.
Scanning Probe Microscopy of self-assembled InAs and InGaAs quantum dots
Quantum dots are structures which are so small (generally < 40 nm) that the free electrons are confined in all three dimensions. The dots are a physical realization of the standard quantum "particle-in-a-box" problem and are sometimes called artificial atoms.
In this atomic force microscope image, the dots appear as bright points. These quantum dots are pyramidal islands of Indium Arsenide (InAs) approximately 5 nanometers tall. The dots are grown on a substrate of Gallium Arsenide (GaAs). The scalloped layers visible across the background are actually steps from one atomic layer to the next in the GaAs crystal. |
Fall 2008
We have successfully expanded the capabilities of the SPM by adding some electronics to the Scanning Tunnelling Microscope configuration so that we can do ballistic electron emission microscopy (BEEM). Austin Carter '05 and Kathy McCreary '06 both did excellent Senior I.S projects modifying the scope and characterizing the new measurements we're making. Danny Shai (REU Senior Researcher 2007) made dramatic improvements in the technique used to contact the surface with the BEEM probe, and Richard Sampson (REU 2008) incorporated better electronics and successfully observed BEEM from a Au:GaAs sample. The work continues, as we develop new samples and work to incorporate our new Conductive AFM module into the system.
REU Summer 2004
During the summer of 2004, Annie Erbsen used the atomic force microscope (AFM) to characterize the uniformity of the dot height and the surface density of the dots for two samples of InAs dots grown on GaAs. |
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Stephen Poprocki wrote an adaptive program to count the quantum dots and measure their height relative to the local dot background. |
