Vacancy clustering and acceptor activation in nitrogen-implanted ZnO

The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted n-type hydrothermally grown bulk ZnO has been investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature 220 keV N implantation using doses in the low 10 exp 15 cm exp −2 range induces small and big vacancy clusters containing at least 2 and 3–4 Zn vacancies, respectively. The small clusters are present already in as-implanted samples and remain stable up to 1000°C with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at 600°C is associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at 800°C results in a dramatic decrease in the free electron concentration correlated with activation of 10 exp 16–10 exp 17cm exp −3 acceptors likely to be N and/or Li related. The samples remain n type, however, and further annealing at 1000°C results in passivation of the acceptor states while the big clusters dissociate.Peer reviewe

Photoluminescence imaging under applied bias for characterization of Si surface passivation layers

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Iron related donor-like defect in zinc oxide

Hydrothermally grown ZnO samples, annealed in Zn-rich and O-rich ambients, have been investigated by deep level transient spectroscopy. A clear correlation has been found between the annealing treatment and the formation/suppression of two defect levels at ∼0.19 (E2) and ∼0.54 (E4) eV below the conduction band edge (Ec). Moreover, a close proportionality over more than three orders of magnitude has been established between the concentration of E2 and that of Fe, as determined by secondary ion mass spectrometry. Based on the above observations and previous reports in the literature, Fe on Zn-site is a likely candidate for E2. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing

Formation kinetics of trivacancy-oxygen pairs in silicon

The formation of donor and acceptor states of the trivacancy-oxygen (V 3O) complex in p- and n-type silicon, respectively, has been studied in detail by means of deep level transient spectroscopy. The samples were irradiated with 1.8 MeV protons, and it was found that acceptor and donor states of V 3 disappear at annealing temperatures below 200 °C, with a transition from the metastable (110) planar configuration to the stable fourfold coordinated configuration. Annealing above 200 °C unveils the formation of two levels with energy positions at Ec  − 0.34 eV and Ec  − 0.46 eV in n-type samples and two levels at Ev  + 0.24 eV and Ev  + 0.11 eV in p-type samples. (Ec and Ev denote the conduction and valence band edge, respectively.) The amplitudes of these levels show an almost one-to-one correlation with those of the V 3-related levels occurring after irradiation. In accordance with recent reports in the literature, the emerging levels are ascribed to the V 3O complex; single and double negative charge states in n-type samples and single and double positive charge states in p-type samples. By undertaking isothermal formation of the V 3O complex in p-type samples which exhibits first-order kinetics, the diffusivity of V 3 in the neutral charge state is determined to be (8.5 ± 3.5) × 10−2 exp [−(1.50 ± 0.04) eV/kT] cm2/s

Defect stabilization and reverse annealing in ZnO implanted with nitrogen at room and cryogenic temperature

Despite the fact that nitrogen is a potential acceptor dopant and one of the most studied elements in ZnO, lacking understanding of associated defects and their thermal evolution limits realization of reliable p-type doping of ZnO. Here, we use ion implantation to introduce N at room temperature (RT) and 15 K in ZnO samples with/without a pre-existing buried disorder layer formed by Ag ion bombardment aligned along the [0001] direction. The buried layer contains a high concentration of extended defects, which act as traps for migrating point defects. Channeling analysis shows that reverse annealing occurs in all the N implanted samples during post-implant heat treatment above 600 °C with strong non-linear additive damage accumulation in the co-implanted samples. The reverse annealing effect is less stable in the RT co-implanted sample and the data suggest that a high local concentration of intrinsic point defects, like Zn interstitials, promotes the stability of the N-defect clusters responsible for the reverse annealing. This suggestion is also corroborated by enhanced and defect-mediated Ag outdiffusion at 1100 °C in the RT co-implanted samples

Transformation of divacancies to divacancy-oxygen pairs in p-type Czochralski-silicon; mechanism of divacancy diffusion

In this work, a comprehensive study on the transition of divacancy (V2) to divacancy-oxygen (V2O) pairs in p-type silicon has been performed with deep level transient spectroscopy (DLTS). Czochralski grown, boron doped p-type, silicon samples, with a doping concentration of 2 × 1015 cm−3 and oxygen content of 7.0 ± 1.5 × 1017 cm−3, have been irradiated with 1.8 MeV protons. Isothermal annealing at temperatures in the range of 200 °C–300 °C shows a close to one-to-one correlation between the loss in the donor state of V2 and the formation of the donor state of V2O, located at 0.23 eV above the valence band edge. A concurrent transition takes place between the single acceptor states of V2 and V2O, as unveiled by injection of electrons through optical excitation during the trap filling sequence of the DLTS measurements. Applying the theory for diffusion limited reactions, the diffusivity of V2 in the studied p-type samples is determined to be (1.5 ± 0.7) × 10−3exp[−(1.31 ± 0.03) eV/kT] cm2/s, and this represents the neutral charge state of V2. Further, the data seem to favor a two-stage diffusion mechanism involving partial dissociation of V2, although a one-stage process cannot be fully excluded

Silver migration and trapping in ion implanted ZnO single crystals

Potentially, group-Ib elements (Cu, Ag, and Au) incorporated on Zn sites can be used for p-type doping of ZnO, and in the present paper, we use ion implantation to introduce Ag atoms in wurtzite ZnO single crystals. Monitoring the Li behavior, being a residual impurity in the crystals, as a tracer, we demonstrate that Zn interstitials assist the Ag diffusion and lead to Ag pile-up behind the implanted region after annealing above 800 °C. At even higher temperatures, a pronounced Ag loss from the sample surface occurs and concurrently the Ag atoms exhibit a trap-limited diffusion into the crystal bulk with an activation energy of ∼2.6 eV. The dominant traps are most likely Zn vacancies and substitutional Li atoms, yielding substitutional Ag atoms. In addition, formation of an anomalous multipeak Ag distribution in the implanted near-surface region after annealing can be attributed to local implantation-induced stoichiometry disturbances leading to trapping of the Ag atoms by O and Zn vacancies in the vicinity of the surface and in the end-of-range region, respectively. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing