Dresden 2006 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 33: GaN: Preparation and characterization
HL 33.7: Vortrag
Mittwoch, 29. März 2006, 16:00–16:15, BEY 154
Nitrogen-15 and Gallium-71 nuclear magnetic relaxation measurements in GaN — •Anthony Kent, Robin Morris, Helen Geen, C Thomas Foxon, and Sergei Novikov — School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
We have grown by RF plasma-assisted molecular beam epitaxy (PA-MBE) zinc-blende crystal structure GaN using an isotopically pure nitrogen-15 source. We have measured the nuclear spin-lattice (T1) and spin-spin (T2) relaxation times using pulsed NMR at 20 MHz. For Gallium-71 we found T1 was of order seconds at low temperature, and 1/T1 proportional to T1/2 where T is the temperature. This is characteristic of semiconductors in which the spin-lattice relaxation is mediated by mobile electrons and allows us to estimate the free carrier concentration. The spin lattice relaxation time was found to be much longer for nitrogen-15, of order minutes, and the temperature dependence more characteristic of an insulator. This suggests that the free electron-nuclear coupling is weaker for nitrogen-15 compared with Gallium-71. We also show that illumination of the sample by band-gap UV light with circular polarization resulted in hyperpolarization of the Nitrogen-15 and an increase in the NMR signal amplitude.