Mg and Si dopant incorporation and segregation in GaN

Abstract

The surface segregation of Mg and Si dopant species and their atomic incorporation sites in GaN films grown by metal-organic vapour phase epitaxy (MOVPE) on sapphire (0001) substrates have been analysed by X-ray photoemission spectro-microscopy and X-ray standing waves (XSW). As revealed by spectro-microscopy, both Mg and Si tend to segregate to the surface. In case of Mg, an enhanced surface dopant concentration is found even after sputter-removal of several tens of nanometres, which confirms a segregation mechanism proposed earlier [S. Figge et al., Appl. Phys. Lett. 81, 4748 (2002)]. Si doping has been found to result in the formation of facetted grooves in the GaN films. The surface silicon concentration at the facets is determined to be about 2.5 times higher as compared to the planar (0001) surface by micro-spectroscopy. XSW results show that with increasing Mg dopant concentration, non-substitutional lattice sites are progressively occupied. The results can quantitatively be explained by Mg atoms incorporated in an anti-bixbyite-like structure and is related to inversion domain boundaries. For Si doping, no evidence is found for the occupation of non-substitutional sites. However, a decrease in crystal quality is observed with increasing Si concentration.X-ray photoemission micrograph of a Si doped GaN film showing a facetted groove at the lower left corner of the image. The local spectra (see inset) reveal Si enrichment at the facets.

Negative‐U Properties of the Deep Level E3 in ZnO

“…The implantation of zinc ions does not change the E3 concentration in HT bulk ZnO. [49] The same result was reported for ZnO thin films: the implantation of zinc [38] or nickel ions [46] had no impact on the E3 defect density. Gu et al reported an increase of the E3 concentration in MG bulk ZnO samples after nitrogen ion implantation.…”

“…We have characterized the properties of the deep level defect E3 in several earlier investigations. [16,19,28,33,36,38,42,46,48,53,56,63,82] In these experiments bulk samples obtained from Tokyo Denpa as well as heteroepitaxial thin films grown by pulsed laser deposition were used. Overall, about a hundred samples containing the E3 center were and are available.…”

“…At RT, Li Zn cannot be detected by EPR. This implies that E3 is not connected to Li Zn since it also was observed in thin film samples that are not Li contaminated (e.g., in thin films grown by pulsed laser deposition [16,19,28,36,38,42,46,48,53,56,63,82] ). The EPR signal of the shallow donor is only observable after optical excitation (except for the 980 nm laser) and for T 80 K. The line width shows a strong temperature dependence (it is 0.9 G at 80 K and 4.3 G at 30 K).…”

“…During warm-up, the ions transfer back to the trivalent state X 3þ with thermal activation energies of 240 meV for Fe 2þ and 280 meV for Ni 2þ . [27] Schmidt et al [46] showed later that a nickel related state in ZnO had a higher thermal activation energy than E3. Vines and co-workers studied the behavior of E3 in hydrothermal bulk material upon thermal annealing and compared it to the amount of impurities within the samples after each annealing step.…”

Nickel Oxide–Based Heterostructures with Large Band Offsets

“…Because the loss mechanism is not present for the Schottky reference structure, the defect in question must be specifically related to the usage of NiO. Ni as an impurity in ZnO has been investigated, e.g., by Schmidt et al [35] where the authors show Ni incorporation to lead to the formation of an electronically defect having two detectable charge transistion within the ZnO band gap. The deeper of these two can be (de-)populated by UV photons.…”