Dopant Distribution in Atomic Layer Deposited ZnO:Al Films Visualized by Transmission Electron Microscopy and Atom Probe Tomography

Abstract

The maximum conductivity achievable in Al-doped ZnO thin films prepared by atomic layer deposition (ALD) is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the three-dimensional distribution of Al atoms in the ZnO host material matrix has been examined on the atomic scale using a combination of high-resolution transmission electron microscopy (TEM) and atom probe tomography (APT). Although the Al distribution in ZnO films prepared by so-called “ALD supercycles” is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers is observed with a full-width–half-maximum of ∼2 nm. In addition, an enrichment of the Al at grain boundaries is observed. The low doping efficiency for local Al densities > ∼1 nm–3 can be ascribed to the Al solubility limit in ZnO and to the suppression of the ionization of Al dopants from adjacent Al donors.

Atomic-layer-deposited Al-doped zinc oxide as a passivating conductive contacting layer for n+-doped surfaces in silicon solar cells

“…a lower cycle ratio n) results in a higher carrier density N e . At the same time, the carrier mobility μ e decreases with increasing doping level, which is attributed to a combination of enhanced ionized impurity scattering from active dopants [84], scattering from inactive dopants and possibly increased grain boundary scattering due to a reduction of grain size [75,85]. Upon annealing the uncapped ZnO:Al samples, a strong reduction in both carrier density and mobility is observed.…”

“…Because of this, it is hypothesized that for the ZnO:Al samples, the reduction of Hall mobility occurring at high annealing temperatures can be due to segregation of Al into e.g. Al 2 O 3 clusters at the grain boundaries [85].…”

Investigation of an atomic‐layer‐deposited Al2O3 diffusion barrier between Pt and Si for the use in atomic scale atom probe tomography studies on a combinatorial processing platform

“…10 Therefore, a conformal and stable coating which protects the Si tip from unwanted reactions with the thin film material of interest needs to be developed. Here, we investigate a 20-nm-thick Al 2 O 3 thin film deposited by plasma enhanced atomic layer deposition (PE-ALD) [11][12][13] as a protection layer. Deposition of an Al 2 O 3 layer on a needle-shaped specimen was reported in Kuduz et al 14 Different from the present work, Al 2 O 3 was chosen to serve as an electrical insulator in tunneling magneto-resistance layers in Kuduz et al 14 Moreover, the Al 2 O 3 layer in Kuduz et al 14 was produced by sputter deposition on a single tip, while we applied ALD to achieve conformal and dense Al 2 O 3 layers simultaneously on a tip array of 36 identical tips.…”

X-ray Diffraction, XPS, and Raman Spectroscopy of Coated ZnO:Al (1—7 at%) Nanoparticles

“…Techniques addressed to study doped ZnO effects on the properties of AZO films including electrospray method [9], pulsed laser deposition (PLD) [10], RF magnetron sputtering technique [11], atomic layer deposition [12], chemical bath deposition (CBD) [13], sol-gel process [14,15], etc. have been used to deposit AZO nanoparticles.…”