In this letter, we report the results of ion implantation of GaN using 28Si and 24Mg species. Structural and electrical characterizations of the GaN thin films after thermal annealing show that native defects in the GaN films dominate over implant doping effects. The formation energies of the annealing induced defects are estimated to range from 1.4 to 3.6 eV. A 40 keV 1014 cm−2 Mg implant results in the decrease of the free-carrier concentration by three orders of magnitude compared to unimplanted GaN up to an annealing temperature of 690 °C. Furthermore, we have observed the correlation between these annealing-induced defects to both improved optical and electrical properties.

The structural and electrical properties of metalorganic chemical vapor deposition-grown Pb(Zr0.35Ti0.65)O3 thin films ranging in thickness from 700 to 4000 Å have been investigated. Cross-sectional scanning electron microscopy showed that these films are columnar, with grains extending through the thickness of the film. High-resolution x-ray diffraction showed that while the thickest films are tetragonal, with reflections corresponding to a-type and c-type domains, films thinner than 1500 Å are not. Electron backscatter diffraction and hysteresis loop measurements showed that the thinnest films are ferroelectric and have a rhombohedral crystal structure.

Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O3/Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic O18 was incorporated as a tracer into bare Pb(Zr,Ti)O3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of O18 tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of O18 tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films.

In the process of fatiguing Ir/Pb(Zr0.35Ti0.65)O3/Pt capacitors we have observed the splitting and separation of both the positive and negative switching currents into two distinct peaks. By measuring the current response to a post-fatigue, triangular, voltage waveform, we have observed a shift of the majority of the switching current to higher voltages and, eventually, beyond the voltage testing range. At high fatigue cycle numbers, this current peak shift is large enough to reveal a smaller switching current peak whose position remains invariant. Subsequent higher amplitude switching pulses access the high coercive voltage switching peaks, returning the remanent polarization values, though not the overall switching profile, to unfatigued levels. Pulse polarization measurements reveal that the switchable polarization that appears lost at lower testing voltages is highly recoverable when higher voltages are applied. Thus, the fatigue cycling appears to primarily increase the polarization switching resistance while inducing very little irrecoverable switching loss. Finally, we measured increased resistance to switching with fatigue cycling even when the majority of the capacitor volume was no longer switching during the fatigue pulses, suggesting that only voltage cycling, and not the concomitant polarization switching, are necessary to induce fatigue.

The microstructure and characteristic defects of heteroepitaxial GaN films grown on sapphire using molecular beam epitaxy (MBE) and metal-organic-chemical-vapor-deposition (MOCVD) methods and of homoepitaxial GaN grown on bulk substrates are described based on transmission electron microscopy (TEM), x-ray diffraction, and cathodoluminescence (CL) studies. The difference in arrangement of dislocations along grain boundaries and die influence of buffer layers on the quality of epitaxial films is described. The structural quality of GaN epilayers is compared to diat of bulk GaN crystals grown from dilute solution of atomic nitrogen in liquid gallium. The full width at half maximum (FWHM) of the x-ray rocking curves for these crystals was in the range of 20–30 arc sec, whereas for the heteroepitaxially grown GaN the FWHM was in the range of 5–20 arc min. Homoepitaxial MBE grown films had FWHMs of about 40 arc sec. The best film quality was obtained for homoepitaxial films grown using MOCVD; these samples were almost free from extended defects. For the bulk GaN crystals a substantial difference in crystal perfection was observed for the opposite sides of the plates shaped normal to the c direction. On one side the surface was almost atomically flat, and the underlying material was free of any extended structural defects, while the other side was rough, with a high density of planar defects. This difference was related to the polarity of the crystal. A large difference in crystal stoichiometry was also observed within different sublayers of the crystals. Based on convergent beam electron diffraction and cathodoluminescence, it is proposed that GaN antisite defects are related to the yellow luminescence observed in these crystals.