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Shallow donor

About: Shallow donor is a research topic. Over the lifetime, 1855 publications have been published within this topic receiving 46232 citations.


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Journal ArticleDOI
TL;DR: A first-principles investigation, based on density functional theory, produces strong evidence that hydrogen acts as a source of conductivity: it can incorporate in high concentrations and behaves as a shallow donor.
Abstract: Zinc oxide, a wide-band-gap semiconductor with many technological applications, typically exhibits n-type conductivity. The cause of this conductivity has been widely debated. A first-principles investigation, based on density functional theory, produces strong evidence that hydrogen acts as a source of conductivity: it can incorporate in high concentrations and behaves as a shallow donor. This behavior is unexpected and very different from hydrogen's role in other semiconductors, in which it acts only as a compensating center and always counteracts the prevailing conductivity. These insights have important consequences for control and utilization of hydrogen in oxides in general.

2,970 citations

Journal ArticleDOI
TL;DR: Vlasenko and Watkins as mentioned in this paper showed that the oxygen vacancy VO is not a shallow donor, but has a deep e(2+∕0) level at ∼10eV below the conduction band.
Abstract: The electronic properties of ZnO have traditionally been explained by invoking intrinsic defects In particular, the frequently observed unintentional n-type conductivity has often been attributed to oxygen vacancies We report first-principles calculations showing that the oxygen vacancy VO is not a shallow donor, but has a deep e(2+∕0) level at ∼10eV below the conduction band The negative-U behavior that causes the 1+charge state to be unstable is associated with large local lattice relaxations We present a detailed configuration coordinate diagram, which allows us to provide a detailed interpretation of recently reported ODEPR (optically detected electron paramagnetic resonance) measurements [L S Vlasenko and G D Watkins, Phys Rev B 71, 125210 (2005)]

1,941 citations

Journal ArticleDOI
TL;DR: In this article, the metastable phase anatase has been shown to have a wider optical absorption gap than rutile thin films, which is consistent with the high mobility, bandlike conduction observed in anatase crystals.
Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

1,560 citations

Journal ArticleDOI
TL;DR: In this paper, the optical properties of excitonic recombinations in bulk, n-type ZnO are investigated by photoluminescence (PL) and spatially resolved cathodoluminecence (CL) measurements.
Abstract: The optical properties of excitonic recombinations in bulk, n-type ZnO are investigated by photoluminescence (PL) and spatially resolved cathodoluminescence (CL) measurements. At liquid helium temperature in undoped crystals the neutral donor bound excitons dominate in the PL spectrum. Two electron satellite transitions (TES) of the donor bound excitons allow to determine the donor binding energies ranging from 46 to 73 meV. These results are in line with the temperature dependent Hall effect measurements. In the as-grown crystals a shallow donor with an activation energy of 30 meV controls the conductivity. Annealing annihilates this shallow donor which has a bound exciton recombination at 3.3628 eV. Correlated by magnetic resonance experiments we attribute this particular donor to hydrogen. The Al, Ga and In donor bound exciton recombinations are identified based on doping and diffusion experiments and using secondary ion mass spectroscopy. We give a special focus on the recombination around 3.333 eV, i.e. about 50 meV below the free exciton transition. From temperature dependent measurements one obtains a small thermal activation energy for the quenching of the luminescence of 10 ± 2 meV despite the large localization energy of 50 meV. Spatially resolved CL measurements show that the 3.333 eV lines are particularly strong at crystal irregularities and occur only at certain spots hence are not homogeneously distributed within the crystal contrary to the bound exciton recombinations. We attribute them to excitons bound to structural defects (Y-line defect) very common in II–VI semiconductors. For the bound exciton lines which seem to be correlated with Li and Na doping we offer a different interpretation. Li and Na do not introduce any shallow acceptor level in ZnO which otherwise should show up in donor–acceptor pair recombinations. Nitrogen creates a shallow acceptor level in ZnO. Donor–acceptor pair recombination with the 165 meV deep N-acceptor is found in nitrogen doped and implanted ZnO samples, respectively. In the best undoped samples excited rotational states of the donor bound excitons can be seen in low temperature PL measurements. At higher temperatures we also see the appearance of the excitons bound to the B-valence band, which are approximately 4.7 meV higher in energy. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

1,550 citations

Journal ArticleDOI
TL;DR: In this paper, the role of oxygen vacancies and various impurities in the electrical and optical properties of the transparent conducting oxide β-Ga2O3 was investigated using hybrid functionals.
Abstract: Using hybrid functionals we have investigated the role of oxygen vacancies and various impurities in the electrical and optical properties of the transparent conducting oxide β-Ga2O3. We find that oxygen vacancies are deep donors, and thus cannot explain the unintentional n-type conductivity. Instead, we attribute the conductivity to common background impurities such as silicon and hydrogen. Monatomic hydrogen has low formation energies and acts as a shallow donor in both interstitial and substitutional configurations. We also explore other dopants, where substitutional forms of Si, Ge, Sn, F, and Cl are shown to behave as shallow donors.

713 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202310
202221
202136
202050
201940
201842