Back to Table of Contents

43430-GB10
T2 Spin Lifetime Measurements in GaAs, A1GaAs, and InGaAs Layers and Quantum Wells via Optically Detected Electron Spin Echo

John S. Colton, University of Wisconsin (La Crosse)

The major goal of this research has been to study electron spin lifetimes in GaAs and related semiconductors, via optical and microwave resonance techniques. Various aspects of the research project are discussed below.

1. Construction of a 10 GHz microwave resonant cavity for use in optically-detected magnetic resonance experiments. A microwave resonant cavity is typically used to amplify the microwave field in magnetic resonance experiments. Our requirements were atypical however, and necessitated a lot of individual design and testing. Our final cavity design had several novel features:

• a high-dielectric material to enable ~10 GHz operation despite having an outer diameter smaller than 25 mm (in order to fit in our magnet bore)

• a variable frequency from approx. 8 to 12 GHz

• optical access of the sample

• an incorporated pseudo-Helmholtz coil to perform simultaneous nuclear resonance

Simulations were carried out via the CST Microwave Studio software package. Experimental testing of the cavity was performed through ODMR of a reference zinc-doped InP sample. Testing of the accompanying Helmholtz coil was performed via optically-detected nuclear magnetic resonance of a GaAs sample.

2. ODMR at ~1T, detected via Kerr rotation. The detection technique of Kerr rotation—the rotation of linear polarization in the reflected beam, which is proportional to the magnetization of the sample—was employed to observe magnetic resonance of a very lightly-doped GaAs sample. The simultaneous control of the nuclear spins enabled many details involving the nuclear-electron interaction to be studied.

3. Ordering of additional equipment—Many pieces of experimental equipment needed for the planned Kerr rotation spin resonance experiments were researched and ordered. These include the following:

• Toptica tunable diode laser

• New Focus balanced diode detector

• SRS lockin amplifier

• Tektronix rf frequency function generator

• Amplifier Research rf amplifier

• PIN diode microwave switch from American Microwave Corporation

• Various other miscellaneous optical, microwave, and hardware components

4. Dissemination of results

a. Results discussed in last year's Annual Report were submitted and accepted for publication: “Anomalous magnetic field dependence of the T1 spin lifetime in a lightly-doped GaAs sample,” J.S. Colton, et al., Phys. Rev. B 75, 205201 (2007).

b. Some results of the microwave cavity design and testing were presented at an APS March Meeting talk: “Development of an 8-12 GHz variable frequency microwave resonant cavity for optically-detected magnetic resonance (ODMR) of GaAs-related semiconductors,” J.S. Colton, et al., Abstract V12.00010, APS March Meeting, Denver CO (Mar 2007). Much more detailed results are currently being written up for submission to Review of Scientific Instruments.

c. The general topic of studying electronic spin in semiconductors (including many of my own results) was presented as an invited colloquium talk for Brigham Young University: “Quantum computing and electron spins in semiconductors,” J.S. Colton, BYU Physics Department Colloquium, Provo UT, Feb 7, 2007

d. Some specific spin lifetime findings in GaAs were presented as an invited seminar talk at University of Wisconsin, Madison: “Spin lifetime measurements in n-GaAs,” J.S. Colton, et al., talk to the Condensed Matter Physics group at U.W. Madison's Physics Department, Madison, WI, Oct 13, 2006.

e. The results of the ODMR via Kerr rotation experiments are being prepared for publication.

5. Training of undergraduates. I have included undergraduate research students in nearly all aspects of this work. Specifically, during the time period from 9/1/06 – 8/31/07, seven undergraduate students worked with me on these projects. For research work that took place during the school year, the students typically received course credit; for research work outside the normal semesters (i.e. Jan 2007 and summer 2007), I have been able to pay the students a stipend using (primarily) this research grant.

Susie Allemann – Summer 2007. She helped in all of the experiments conducted during that time.

Andrew Gierke – Summer 2007. In addition to generally with the experiments during that time (including data collection), he more specifically helped design a circuit whereby we could resonate the nuclei simultaneously with the electrons.

Joseph Lanksa – Fall 2006 semester, and during Jan 2007 term. He spent much of his time learning the LabView computer program, used to control equipment.

Lindsay Oestreich – Fall 2006 semester. She mainly helped design the supporting structure for the resonant microwave cavity.

Paul Schroeder – Mr. Schroeder worked with me during Fall 2006 semester and Jan 2007 term. He helped with my research website, with ordering equipment, and with the actual data collection during experiments.

Andrew Stokes – Fall 2006 semester. His main task was to test out some new microwave equipment.

Lee Wienkes – Fall 2006 semester, January 2007 term, Spring 2007 semester, and Summer 2007. He has assisted heavily in all aspects of the experimental research, including design, construction, and testing of the microwave cavity; writing programs to control the equipment; and assisting with the actual data collection during experiments.

Back to top