Isochronal and isothermal diffusion experiments of gallium (Ga) in zinc oxide (ZnO) have been performed in the temperature range of 900-1050 C. The samples used consisted of a sputterdeposited and highly Ga-doped ZnO film at the surface of a single-crystal bulk material. We use a novel reaction diffusion (RD) approach to demonstrate that the diffusion behavior of Ga in ZnO is consistent with zinc vacancy (V Zn) mediation via the formation and dissociation of Ga Zn V Zn complexes. In the RD modeling, experimental diffusion data are fitted utilizing recent density-functional-theory estimates of the V Zn formation energy and the binding energy of Ga Zn V Zn. From the RD modeling, a migration energy of 2.3 eV is deduced for Ga Zn V Zn , and a total/effective activation energy of 3.0 eV is obtained for the Ga diffusion. Furthermore, and for comparison, employing the so-called Fair model, a total/effective activation energy of 2.7 eV is obtained for the Ga diffusion, reasonably close to the total value extracted from the RD-modeling.

Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200–700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed.

The implantation of aluminum into 4H-SiC is studied using secondary ion mass spectrometry. In particular, two-dimensional concentration profiles are obtained, which allow the investigation of lateral straggling and its dependence on the crystallographic orientation. A high dose, medium energy aluminum implantation is studied in great detail. It shows an asymmetric distribution due to the 4°-off axis growth of the epitaxial layer. The lateral straggling is found to be in the range of several micrometers for a concentration of 1×1015 cm−3, which is contrary to the expectation given by most simulation studies. Implantations performed at different orientations support the idea that lateral straggling highly depends on the particular channeling opening.

The influence of Fermi level position and annealing ambient on the zinc vacancy V Zn generation and Al diffusion is studied in monocrystalline zinc oxide (ZnO). From secondary-ion mass spectrometry and positron annihilation spectroscopy results, a quadratic dependence between the concentrations of V Zn and Al is established, demonstrating the Fermi level dependence of the formation of the electrically compensating −2 charge state of V Zn in conductive n-type ZnO crystals. In contrast, thermal treatment in the zinc-rich ambient is shown to efficiently reduce the V Zn concentration and related complexes. Using a reaction-diffusion model, the diffusion characteristics of Al at different donor background concentrations are fully accounted for by mobile (Al Zn V Zn) − pairs. These pairs form via the migration and reaction of isolated V 2− Zn with the essentially immobile Al + Zn. We obtain a migration barrier for the (Al Zn V Zn) − pair of 2.4 ± 0.2 eV, in good agreement with theoretical predictions. In addition to strongly alter the shape of the Al diffusion profiles, increasing the donor background concentration also results in an enhanced effective Al diffusivity, attributed to a reduction in the V 2− Zn formation energy as the Fermi level position increases.

The annealing behavior of the normalOH−LiZn center in ZnO, which leads to a local vibrational mode at 3577thinmathspacecm−1, has been studied. Infrared absorption measurements confirm the previous findings that the center dissociates already at temperatures higher than about 500∘C and an apparent stability up to 1250∘C is due to efficient retrapping of H by LiZn. Secondary ion mass spectrometry data indicate that Fe impurities prevent a reformation of normalOH−LiZn after dissociation. The formation of Fe −Li complexes is proposed as a prevailing mechanism for this behavior.