Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: A case study of InN

Abstract

We present a comprehensive study of vacancy and vacancy-impurity complexes in InN combining positron annihilation spectroscopy and ab initio calculations. Positron densities and annihilation characteristics of common vacancy-type defects are calculated using density functional theory, and the feasibility of their experimental detection and distinction with positron annihilation methods is discussed. The computational results are compared to positron lifetime and conventional as well as coincidence Doppler broadening measurements of several representative InN samples. The particular dominant vacancy-type positron traps are identified and their characteristic positron lifetimes, Doppler ratio curves, and line-shape parameters determined. We find that indium vacancies (V In ) and their complexes with nitrogen vacancies (V N ) or impurities act as efficient positron traps, inducing distinct changes in the annihilation parameters compared to the InN lattice. Neutral or positively charged V N and pure V N complexes, on the other hand, do not trap positrons. The predominantly introduced positron trap in irradiated InN is identified as the isolated V In , while in as-grown InN layers V In do not occur isolated but complexed with one or more V N . The number of V N per V In in these complexes is found to increase from the near-surface region toward the layer-substrate interface.

Increased p-type conductivity in GaNxSb1−x, experimental and theoretical aspects

“…The conventional interpretation of the S parameter as an indicator of open-volume is thus not necessarily correct for strongly cation-anion-mismatched compounds such as GaNSb studied here, an observation already made in the case of InN. 47 Results obtained with the atomic superposition (ATSUP) method 53 for the calculated structures give information on the contributions of different electronic shells and their relative intensities in the Doppler broadening spectrum. The systematic trend in the ratio curves for the Ga vacancynitrogen complexes compared to the Ga vacancy visible in Fig.…”

“…4 produces ratio curves with the typical fingerprint of group III vacancies in III-V compounds. [45][46][47][48][49] For comparison, in Fig. 5, the coincidence Doppler broadening results for the GaN x Sb 1Àx layers on GaAs along with the p-type bulk GaSb substrate have been scaled to sample 6.…”

Nitrogen and vacancy clusters in ZnO

“…A possible reason is the balance between the amounts of Zn and O vacancies forming the clusters in question. A relatively simple idea, based on the positron data trends in another strongly cation-anion mismatched semiconductor InN, 24 would be that the less stable clusters have more O vacancies. However, this interpretation is subject to more detailed studies (both experimental and computational) on the nature of multivacancy complexes in ZnO.…”

Defect evolution and impurity migration in Na-implanted ZnO

“…34 In its turn, experimental data above the V Zn line combined with high S parameter values indicate large (compared with V Zn ) open-volume defects, i.e., vacancy clusters where both Zn and O atoms are missing, as clusters of only cation vacancies in compound semiconductors do not produce a deviation from the single vacancy line or its extension. 35 The defects in the as-implanted samples (e.g., A 1) are clearly larger in size than a single V Zn , and after annealing (A 2), they evolve into even bigger vacancy clusters with a size of probably at least 3-5 V Zn 's (and a corresponding amount of V O 's). 36 The results from sample A 3 appear to be closer to the V Zn line than the rest of the data, indicating a smaller contribution from Li Zn , correlating with the Li redistribution in Fig.…”