Dr. John Colton, Department of Physics & Astronomy

Proposed Research

The proposed project was to study spin properties of electrons in the semiconductor gallium arsenide (GaAs). Four specific experiments were discussed:

• Optically-detected magnetic resonance of single quantum dots
• Parallel picosecond single qubit operations
• Optically-detected magnetic resonance of spin-LEDs
• Universal scheme for optically-detected spin flip lifetime measurements

Summary of how funds were used/List of students

The funds paid for eight undergraduate students’ salaries to work on this project from Jan 2010 through Dec 2012. The following eight undergraduate students worked on the project during the times indicated, with the MEG grant paying the amount of salary also indicated:
Mitch Jones – Winter 2010, $801
Steve Brown – Winter 2010 – Summer 2010, $367
Dallas Smith – Winter 2010 – Winter 2011, $1242
Scott Thalman – Winter 2010 – Summer 2011, $4405
Ken Clark – Winter 2010 – Fall 2011, $8065
David Meyer – Winter 2011 – Fall 2011, $485
Daniel Craft – Winter 2011 – Fall 2011, $335
Jane Cutler – Winter 2011 – Fall 2011, $299

Total student wages: $16,000 (the numbers given above sum to $15999 due to rounding)

The funds also were used to pay part of the liquid helium/liquid nitrogen costs of the low temperature experiments, in the amount of $2,000/year.

Total cryogen supplies: $4,000

Total funds used: $20,000

Description of scholarly activities

To quickly address the four proposed experiments which were mentioned above:

• Optically-detected magnetic resonance of single quantum dots – We spent several months studying this and got interesting results which we presented at a conference. However, the experiments were inconsistent, given different results from day to day, and as a consequence we did not submit the results for publication.
• Parallel picosecond single qubit operations – This experiment relied on equipment being purchased from another grant, which was not awarded. Consequently nothing was done here.
• Optically-detected magnetic resonance of spin-LEDs – We did some preliminary experiments, but did not get measurable results. The idea is still a sound one, and we plan to return to this experiment in the coming year. Several of the students were involved in getting a large electromagnet functioning for these upcoming experiments.
• Universal scheme for optically-detected spin flip lifetime measurements – This was the most successful of the four proposed experiments, and was the subject of a recently published peer-reviewed journal article (full reference given later) as well as another journal article in preparation.

In addition to those four experiments, the main additional project that several of these students were involved with was measuring luminescence of quantum dots (including time-resolved luminescence).

More details of these scholarly activities can be given upon request.

List of students’ academic deliverables (undergraduate students funded by current and past MEG grants marked with *)

Peer-reviewed journal articles

• “Universal scheme for measuring the electron T1 in semiconductors and application to a

lightly-doped n-GaAs sample,” J. S. Colton, K. Clark*, D. Meyer*, T. Park, D. Smith*, and S. Thalman*, Solid State Comm., published online 3 Dec 2011; doesn’t seem to be in hardcopy yet.

Peer-reviewed journal articles in preparation

• “Light emission beyond 1.6 um from InGaAs quantum dots,” H. Yang, D.J. Kim, J.S. Colton, A.M. Jones*, S. Thalman*, D. Smith*, K. Clark*, and D. Meyer*, submission pending.
• “Spin lifetimes of electrons in a 14 nm quantum well,” J. S. Colton, J. Cutler*, D. Craft*, K. Clark*, D. Meyer*, and T. Park, submission pending.

Senior theses

• M. Jones*, “Photoluminescence of Indium Gallium Arsenide Quantum Dots and Dot Chains,” Apr 2010.
• S. Brown*, “An Object-Oriented Framework For Experimental Control in the Colton Spin Dynamics Laboratory,” Aug 2010.
• D. Smith*, “Optical Measurement of Electron Spin Lifetimes in Gallium Arsenide,” Apr 2011.
• S. Thalman*, “Photoluminescence Lifetimes of Quantum Dots,” Apr 2011.

Conference presentations (reverse chronological)

• “Photoluminescence spectroscopy and transmission electron microscopy imaging of InGaAs quantum dot chains,” T. Park, K. Clark*, D. Meyer*, A. Perry, S. Thalman*, J.S. Colton, H. Yang, Four Corners Section of American Physical Society Meeting, Tucson AZ, Oct 22, 2011.
• “Universal scheme for optically-detected T1 measurements and application to an n = 3E14 cm-3 GaAs sample,” J.S. Colton, T. Park, K. Clark*, D. Craft*, J. Cutler*, D. Meyer*, D. Smith*, and S. Thalman*, Abstract A15.4, American Physical Society March Meeting, Dallas TX (Mar 2011).
• “Using photoluminescence spectroscopy and transmission electron microscopy for observing GaAs quantum dots,” T. Park, K. Clark*, D. Smith*, S. Thalman*, J.S. Colton, H. Yang, Brigham Young University Spring Research Conference, Provo UT, Mar 19, 2011.
• “Photoluminescent properties of InGaAs quantum dot structures,” K. Clark*, J.S. Colton, M. Guerron*, D. Smith*, S. Thalman*, and H. Yang, Brigham Young University Spring Research Conference, Provo UT, Mar 19, 2011.
• “Photoluminescence Lifetimes of InGaAs Quantum Dots,” Scott Thalman* and J.S. Colton, Brigham Young University Spring Research Conference, Provo UT, Mar 19, 2011.
• “Photoluminescent properties of InGaAs quantum dot structures,” K. Clark*, J.S. Colton, M. Guerron, D. Smith*, S. Thalman*, and H. Yang, Abstract L2.3, Four Corners Section of American Physical Society Meeting, Ogden UT, Oct 16, 2010.
• “Photoluminescent lifetime measurements of indium gallium arsenide quantum dot structures using time-correlated single photon counting,” S. Thalman*, J.S. Colton, and H. Yang, Abstract L2.3, Four Corners Section of American Physical Society Meeting, Ogden, UT, Oct 16, 2010.
• “Photoluminescence of indium gallium arsenide quantum dots and dot-chains,” A.M Jones*, J.S. Colton, S. Thalman*, D. Smith*, S. Brown*, Brigham Young University Spring Research Conference, Provo UT, Mar 20, 2010.
• “Time-correlated Single Photon Counting,” S. Thalman*, J.S. Colton, A.M Jones*, S. Brown*, D. Smith*, Brigham Young University Spring Research Conference, Provo UT, Mar 20, 2010.
• “Taming the magnet,” D. Smith*, J.S. Colton, S. Brown*, Brigham Young University Spring Research Conference, Provo UT, Mar 20, 2010.
• “Optically-detected electron spin resonance of self-assembled InAs quantum dots,” J..S. Colton, A.M. Jones*, S. Brown*, D. Smith*, S. Thalman*, and K. Clark*, Abstract B35.2, American Physical Society March Meeting, Portland, OR (Mar 2010).

Evaluation of the mentoring experience

The mentoring experience has been extremely successful! The undergraduate students have learned what must occur to do “real research” and they have made meaningful contributions to it. As always, some experiments were successful and some were not. Many of the students have expressed gratitude to me for including them in this research and being their mentor. I have written numerous letters of recommendation for the students funded by this MEG grant as listed above. Of the ones who have graduated, Mitch Jones is now in a physics graduate program at U. Washington, Dallas Smith is in an optics graduate program at U. Rochester, Scott Thalman is waiting to hear back from several M.D.-Ph.D. programs he applied to, and sadly Steve Brown passed away from cancer after having begun graduate studies in physics at U. Maryland.