Browsing by Author "McGill, S. A."

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    Photoluminescence quantum efficiency of Er optical centers in GaN epilayers
    Ho, V. X.; Dao, T. V.; Jiang, H. X.; Lin, J. Y.; Zavada, J. M.; McGill, S. A.; Vinh, N. Q. (Springer Nature, 2017-01-05)
    We report the quantum efficiency of photoluminescence processes of Er optical centers as well as the thermal quenching mechanism in GaN epilayers prepared by metal-organic chemical vapor deposition. High resolution infrared spectroscopy and temperature dependence measurements of photoluminescence intensity from Er ions in GaN under resonant excitation excitations were performed. Data provide a picture of the thermal quenching processes and activation energy levels. By comparing the photoluminescence from Er ions in the epilayer with a reference sample of Er-doped SiO2, we find that the fraction of Er ions that emits photon at 1.54 mu m upon a resonant optical excitation is approximately 68%. This result presents a significant step in the realization of GaN: Er epilayers as an optical gain medium at 1.54 mu m.
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    Time-resolved differential transmission in MOVPE-grown ferromagnetic InMnAs
    Bhowmick, M.; Merritt, T. R.; Khodaparast, Giti A.; Wessels, B. W.; McGill, S. A.; Saha, D.; Pan, X.; Sanders, G. D.; Stanton, C. J. (American Physical Society, 2012-03-27)
    We measured time-resolved differential transmission in InMnAs for different pump/probe schemes as a function of temperature, laser fluence, and external magnetic field. We observed tunability of the carrier relaxation time. In addition, we found that the sign of the differential transmission changed as a function of probe wavelength. The electronic structure for InMnAs was calculated for B = 0, using an eight-band k.p model, which includes conduction and valence band mixing as well as coupling of electrons and holes to the magnetic Mn impurities. This allows us to explain some of the carrier dynamics and the sign changes in the differential transmission.