Spectroscopic Ellipsometry Study on Tuning the Electrical and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition

Abstract

This work reports the ellipsometry analysis of atomic layer deposition (ALD) films of ZnO doped with Zr to determine parameters like free carrier concentration and mobility. Thin films of zinc oxide (ZnO) and Zr-doped ZnO of thickness ∼100 nm were prepared by atomic layer deposition on sapphire, SiO 2 /Si(100), and Si(100) substrates. Variable-angle spectroscopic ellipsometry was used to study their optical properties in the 0.5− 3.5 eV spectral range. The optical constants were accurately obtained using a model that combines Drude and Tauc−Lorentz oscillators with Bruggeman effective medium approximations, allowing the inclusion of a roughness layer in the optical model. The effect of Zr doping (ca. 1.9−4.4 atom %) was then investigated in both as-prepared samples and samples annealed in the temperature range of 100−300 °C. All of the films exhibited good optical transparency (ca. 70−90% in the visible region). For doping levels below 2.7 atom %, the real part of the dielectric permittivity reveals a semiconductor-to-metal transition in the nearinfrared (NIR) region, as the permittivity goes from positive to negative. Besides, the plasma energy increases with increasing Zr concentration, and both resistivity and carrier concentration exhibit slightly parabolic behaviors, with a minimum of ∼1.5 × 10 −3 Ω cm and a maximum of 2.4 × 10 20 cm −3 , respectively, at the same critical Zr concentration (2.7 atom %). In contrast, the carrier mobility decreases rapidly from 76.0 to 19.2 cm 2 /(V s) with increasing Zr content, while conductivities and carrier mobilities worsen when the annealing temperature increases, probably due to the segregation of ZnO crystals. Finally, the optical band gap is very stable, revealing its interesting independence of substrate composition and annealing temperature, as it collapses to a single master curve when band gap energy is plotted versus free carrier concentration, following the Burstein−Moss effect. Overall, the Zr-doped ZnO films studied here would be a highly desirable system for developing thermally stable transparent conductive oxides (TCOs).

Photonic Characterisation of Indium Tin Oxide as a Function of Deposition Conditions

“…Also, ITO carrier concentrations are typically observed in the range of 10 –10 cm [ 41 , 46 ], similarly to the findings presented herein. We note that varied angle spectroscopic ellipsometry (VASE) is an alternative and very robust, low-noise measurement technique, that has frequently been used for the determination of the properties of TCOs [ 47 , 48 , 49 , 50 ]. VASE, however, also requires a model with assumptions on material parameters, hence, many of the insights we provide here also apply there.…”

Additive Manufacturing of Zn‐Doped ZrO2Architectures

“…The O II and O III peaks can be associated with C═O in hydrocarbon adsorbates or oxygen in Zn(OH) 2 . [76][77][78] In the case of ZrO 2 :Zn5 annealed at 840 °C, the Zr 3d peaks are found at 182.0 eV (Zr I ), 183.9 eV (Zr II ), 184.0 eV (Zr III ), and 186. For the m-ZrO 2, the shift of Zr 3d peaks to lower binding energies compared with t-ZrO 2 .…”

Structural, Optical, and Electrical Properties of Hafnium–Aluminum–Zinc-Oxide Films Grown by Atomic Layer Deposition for TCO Applications

“…In recent decades, there has been increasing interest in transparent conductive oxide (TCO) films such as In 2 O 3 , SnO 2 , ZnO, and their alloys variations, primarily due to their potential applications in electronic and optoelectronic devices including solar cells, LEDs, flat panel displays, thin film transistors, and variety of sensors. − TCOs are characterized by having simultaneously exceptional electrical conductivity and high transmission in the visible range. These properties of the TCO films can be widely tuned by changing various factors such as their growth parameters, composition, doping amount, and post-deposition treatment. − Among many TCO materials, doped ZnO is one of the foremost candidates for next-generation electronic devices, due to its high earth abundance, nontoxicity, biocompatibility, and affordability, contrary to current industry standard indium tin oxide (ITO). − …”

“…These properties of the TCO films can be widely tuned by changing various factors such as their growth parameters, composition, doping amount, and post-deposition treatment. 9 − 15 Among many TCO materials, doped ZnO is one of the foremost candidates for next-generation electronic devices, due to its high earth abundance, nontoxicity, biocompatibility, and affordability, contrary to current industry standard indium tin oxide (ITO). 16 − 18 …”