Local bonding geometry of oxygen implanted in GaN: a depth-dependent study.
The bonding environment of oxygen implanted in GaN is studied using near edge X-ray absorption fine structure spectroscopy at the O-K-edge. The 70 keV oxygen ions form a 200 nm-thick subsurface layer that is highly defective or amorphous depending on the implantation fluence which ranges from 1 x 10(15) cm-2 to 1 x 10(17) cm(-2). The information depth of the fluorescence photons varies from 50 to 63 nm, depending on the angle of incidence. The spectra are simulated using the FEFF8 code and assuming various models, e.g., O interstitial, O substitutional in N sites, Ga and N vacancies, and various polymorphs of Ga2O3. The lattice disorder is modelled by displacing atoms from their equilibrium positions by adding to their Cartesian coordinates random numbers that belong to normal distributions. The simulation results reveal that at the low fluence limit, the O atoms occupy interstitial sites preferentially in the empty channels aligned to the c-axis and in the atomic planes containing the Ga atoms. When the fluence is equal to 1 x 10(16) cm(-2) the O atoms substitute N while at 1 x 10(17) cm(-2) they form mixed GaO(x)N(y) phases with the N/O ratio decreasing with increasing depth, i.e., as we approach the peak of the implanted O profile.
School of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece.
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Katsikini
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Boscherini
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Paloura