Abstract
Dopant diffusion of indium (In) in single crystal zinc oxide is studied by secondary ion mass spectrometry and is interpreted using a reaction–diffusion model that invokes predictions from density functional theory (DFT). An apparent activation energy of 2.2 eV is obtained for the diffusion of In, when the local Fermi-level position is about 0.2 eV below the conduction band edge. The diffusion of In is found to be significantly faster that that reported for the other group III donors, aluminum and gallium, with several orders of magnitude higher effective diffusivities, that can be assigned to a lower migration barrier for the diffusion of In. Furthermore, our results reveal self-consistency in previous DFT results of defect formation- and migration energies. From this, the diffusion of In is suggested to occur through mobile charged zinc vacancies that form intermediate mobile ()− pairs. The pairs in turn dissociate rather readily at the studied temperatures (850 °C–1150 °C), which results in distinct and abrupt diffusion fronts for the In depth distribution profiles.
Highlights
Doping of zinc oxide (ZnO) with donor atoms, such as the group III elements aluminum (Al) and gallium (Ga) is common practice in realizing transparent conductive oxides (TCO) [1,2,3,4]
A migration of In from the In-doped ZnO film into the ZnO bulk is observable above 800 °C, while heat treatments conducted at lower temperatures (600 °C–800 °C) revealed no change in the In distribution
The box shape of the In diffusion profiles are of similar character as that previously reported for Al [11] and Ga [17] in ZnO
Summary
Doping of zinc oxide (ZnO) with donor atoms, such as the group III elements aluminum (Al) and gallium (Ga) is common practice in realizing transparent conductive oxides (TCO) [1,2,3,4]. ZnO is more abundant, and with reported resistivity as low as 8–9 × 10−5 Ω cm for Al- and Ga -doped ZnO [5, 6], i.e. comparable to that of ITO (7.2 × 10−5 Ω cm [4, 7]), makes ZnO desirable for use as a transparent electrode. In addition to Al and Ga, In has been demonstrated to produce highly conductive ZnO layers, where a resistivity of about 8–9 × 10−4 Ω cm was reported for In-doped thin films prepared by spray pyrolysis [9]. RF magnetron sputtering [1]. This should be compared with a resistivity of 1.9 × 10−4 Ω cm and 5.1 × 10−4 Ω cm for
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