The Optical Absorption and Photoluminescence Characteristics of Evaporated and IAD HfO2 Thin Films

Abstract

HfO2 thin films are extensively applied in optical coatings and microelectronic devices. However, film defects, which are vital to the performance of the thin films, are still under intense investigation. In this work, the absorption, photoluminescence, and crystallization characteristics of HfO2 films prepared by electron-beam evaporation and ion-assisted deposition are investigated in detail. Experimental results showed that high-temperature thermal annealing in air resulted in a reduced absorption coefficient, an increased bandgap width, and an increased degree of crystallization. After thermal annealing, an absorption shoulder near 5.8 eV was caused by excitons in the films, which were independent of oxygen vacancy defects and crystallization. Under 6.4 eV (193 nm) laser excitation, the photoluminescence spectrum showed five emission peaks for HfO2 films both with and without thermal annealing. The emission peak near 4.4 eV was generated by the self-trapped exciton, and the peak near 4.0 eV was related to the OH group in the film. The oxygen vacancy defect-induced absorption of HfO2 films in a broad spectral range significantly increased when HfO2 film was re-annealed in Ar gas after first being annealed in air, while the photoluminescence spectrum showed no significant change, indicating that the emission peaks at 2.3, 2.8, and 3.4 eV were not related to oxygen vacancy defects.

Radiation Response of HfOx-Based Resistive Random Access Memory (RRAM) Devices

“…PL spectroscopy was used to analyze the vacancy defects in these films. These oxygen vacancies are very critical for the filament formation processes that govern the RS phenomenon. − The PL data of the pristine sample shown in Figure (a) indicates the presence of oxygen vacancies in the pristine films. Similarly, the PL spectra and the de-convoluted peaks for the SHI-irradiated samples, with different fluence values, are as shown in Figure (a–e).…”

“…Therefore, Ag ions will come to rest only in the substrate. Electronic energy deposition can result in deep defects, trap centers, and other kinds of defects. ,− , These RRAM devices were subjected to different irradiation fluence values (5E10, 1E11, 5E11, 1E12, and 5E12 ions/cm 2 ) to study the effects on their switching performance.…”

Systematic Evolution of Optical Bandgap and Local Chemical State in Transparent MgO and HfO2 Resistive Switching Materials

“…Among the oxides mentioned before, HfO 2 has been extensively studied and found to have a high dielectric constant (≈25), good chemical and thermal stability, excellent transmittance, wide bandgap (≈5.6 eV), and high refractive index, [ 7 ] making it a competitive contender for both resistive switching oxide and optical materials. [ 8 ] In addition, HfO 2 is convenient for various optoelectronic applications like heat mirrors, energy‐efficient windows, and nanophotonic devices.…”

“…To grow the oxide thin film, various techniques were adopted, such as physical vapor deposition, [ 2 ] chemical vapor deposition, [ 13 ] atomic layer deposition, [ 14 ] and ion beam deposition. [ 7 ] In addition, there are other advanced fabrication techniques, such as metal–organic chemical vapor deposition (MOCVD) and MOCVD via vapor–liquid–solid process, which are adapted to synthesize the thin films in reported literature. [ 15,16 ] Likewise, different characterization techniques like X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and ultraviolet‐visible (UV–vis) spectroscopy were performed to investigate the structural, local chemical state information, bandgap, and transparency of the thin films, respectively.…”

Tailoring the Anodic Hafnium Oxide Morphology Using Different Organic Solvent Electrolytes

“…Hafnium oxide (HfO 2 ) with its high thermal, chemical and mechanical stability, as well as its high refractive index and dielectric constant is remarkably appealing for new nanostructure architectures like nanoporous or nanotube (NT) arrays and a large range of applications [5][6][7][8][9][10][11][12]. Having into account the emerging application of anodic TiO 2 nanotubes in DSCs, the question arises about the applicability of self-ordered arrays of anodic HfO 2 for the same purpose.…”