Post-deposition Rapid Thermal Annealing Research Articles

Influence of Terbium Doping and Annealing on the Structural and Optical Characteristics of Sputtered Zinc Oxide Thin Films

This paper studied the structural and luminescent characteristics of undoped and doped-with-Tb3+-ions ZnO films of 200 nm and 600 nm thicknesses, grown via RF magnetron sputtering on (100) silicon substrate in Ar and Ar-O2 plasma. X-ray diffraction (XRD) patterns revealed a strong preferred orientation of ZnO and ZnO:Tb crystals of the wurtzite structure along the c-axis, perpendicular to the substrate. In the as-deposited ZnO:Tb films, the additional crystal phases, namely, Tb2O3, TbO2, and an amorphous phase, were revealed. The as-deposited undoped films were under tensile strain, that increased in the doped films. This proved the incorporation of the Tb3+ ions into the ZnO grains, and agreed with the Raman spectra investigation. The XRD data and atomic force microscopy study showed that Tb doping impeded the growth of grains and columns, respectively. The photoluminescence (PL) spectra of the doped films contained the UV band ascribed to exciton PL, a broad intrinsic defect-related band, and the narrow bands caused by the intra-shell transitions of the Tb3+ ions. Terbium doping suppressed ZnO emissions. The post-deposition rapid thermal annealing at up to 800 °C of both the undoped and doped films promoted tensile strain relaxation, grain growth, improvement in the ZnO crystal structure, and an increase in the exciton PL. The intensity of the Tb3+ PL changed non-monotonically, and was the highest for the film annealed at 600 °C. The conventional thermal annealing promoted the non-monotonic changes in the strains and grain sizes in such a way that, after annealing at 900 °C, their values became the same as in the as-deposited ZnO:Tb film. This structural change was accompanied by a decrease in the exciton and Tb3+ PL intensity. The formation of the Zn2SiO4 phase was observed via XRD, and confirmed via scanning electron microscopy. It was attributed to the interdiffusion through the film/substrate interface. The deposition in the Ar-O2 atmosphere is found to be more preferable for the formation of Tb3+ emission centers in the ZnO matrix.

Effect of Rapid Thermal Annealing on Material, Electrical, and Sensing Characteristics of Ag-Doped CaTiO3-CuO Thin Film Carbon-Dioxide Gas Sensors

The effect of rapid thermal annealing (RTA) on CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensing characteristics of RF-sputtered and Ag-doped CaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -CuO thin films has been studied in this work. The surface morphology, grain size, surface chemical states, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–V</i> characteristics, and sensing ability of the films, have been evaluated for postdeposition RTA at different temperatures (400 °C–600 °C) and time (0–60 s). As the annealing temperature was raised, crystallinity improved and the grain size increased. Indeed, XRD revealed that RTA resulted in strong crystallographic orientation in the films. XPS analysis revealed no changes in the oxidation states and chemical composition of the material. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–V</i> measurements show that the resistance of the film decreases as RTA temperature increases. On the other hand, the sensing characteristics reveal an optimum grain size for the best sensitivity. The films annealed at 500 °C for 60 s, leading to a grain size of about 10 nm, display the highest sensor response of 54%, when exposed to 1000 ppm of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Achieving a high energy storage density in Ag(Nb,Ta)O 3 antiferroelectric films via nanograin engineering

Due to its lead-free composition and a unique double polarization hysteresis loop with a large maximum polarization (<i>P</i>_max) and a small remnant polarization (<i>P</i>_r), AgNbO₃-based antiferroelectrics (AFEs) have attracted extensive research interest for electric energy storage applications. However, a low dielectric breakdown field (<i>E</i>_b) limits an energy density and its further development. In this work, a highly efficient method was proposed to fabricate high-energy-density Ag(Nb,Ta)O₃ capacitor films on Si substrates, using a two-step process combining radio frequency (RF)-magnetron sputtering at 450 ℃ and post-deposition rapid thermal annealing (RTA). The RTA process at 700 ℃ led to sufficient crystallization of nanograins in the film, hindering their lateral growth by employing short annealing time of 5 min. The obtained Ag(Nb,Ta)O₃ films showed an average grain size (<i>D</i>) of ~14 nm (obtained by Debye–Scherrer formula) and a slender room temperature (RT) polarization–electric field (<i>P–E</i>) loop (<i>P</i>_r ≈ 3.8 μC·cm⁻² and <i>P</i>_max ≈ 38 μC·cm⁻² under an electric field of ~3.3 MV·cm⁻¹), the <i>P–E</i> loop corresponding to a high recoverable energy density (<i>W</i>_rec) of ~46.4 J·cm⁻³ and an energy efficiency (<i>η</i>) of ~80.3%. Additionally, by analyzing temperature-dependent dielectric property of the film, a significant downshift of the diffused phase transition temperature (<i>T</i>_M2–M3) was revealed, which indicated the existence of a stable relaxor-like AFE phase near the RT. The downshift of the <i>T</i>_M2–M3 could be attributed to a nanograin size and residual tensile strain of the film, and it led to excellent temperature stability (20–240 ℃) of the energy storage performance of the film. Our results indicate that the Ag(Nb,Ta)O₃ film is a promising candidate for electrical energy storage applications.

Effects of rapid thermal annealing temperature on NO2 gas sensing properties of p-type mixed phase tin oxide thin films

Effects of the rapid thermal annealing (RTA) temperature on the NO2 gas sensing properties of p-type SnOX thin films were investigated. The SnOX thin films were deposited using radio-frequency magnetron sputtering and subjected to RTA at 200 °C, 250 °C, and 300 °C. The deposited SnOX thin films contained both p-type SnO and n-type SnO2 components, but the SnO was the dominant phase. The amount of SnO2 components increased with increasing RTA temperature, but the highest amount of oxygen vacancy (OVac) states was observed in the SnOX thin film annealed at 250 °C. The surface roughness of the SnOX thin film decreased as the RTA temperature increased. The SnOX thin film subjected to RTA at 250 °C exhibited a significantly higher maximum sensing response to NO2 (4.25–10 ppm NO2 at 60 °C) than those of the films treated at 200 °C (1.13) or 300 °C (0.92). The higher response was attributed to the larger amount of SnO2 and OVac in the thin film and large number of defects and cracks on the film surface. The experimental results demonstrated that the post-deposition RTA temperature considerably affects the NO2 sensing properties of the p-type SnOX-based gas sensors.

Influence of rapid thermal annealing time on physical properties of Mg and F co-doped ZnO thin films deposited by radio frequency magnetron sputtering

• Mg-F co-doped ZnO (MFZO) thin films are deposited by magnetron sputtering. • Conductivity of MFZO films increases by 37% after the rapid thermal annealing. • The average visible transmittances of the annealed MFZO films exceed 93%. • The annealed MFZO film achieves a high figure of merit (FOM) of 1.18 × 10-2 Ω-1. • The high-FOM MFZO thin films could be used as transparent conducting films. Transparent conducting oxides are commonly used in flat-panel displays, solar cells, light emitting diodes, and other optoelectronic devices. In this study, transparent conducting Mg and F co-doped ZnO (MFZO) thin films were prepared by using radio frequency magnetron sputtering and a post-deposition rapid thermal annealing (RTA) was carried out at 400°C in vacuum. To study the influence of RTA on structural, electrical, and optical properties of the MFZO thin films, the RTA processing time is varied (0–120 s). X-ray diffraction analysis showed that the co-doping of 3.0 at% Mg and 6.0 at% F did not change the (0 0 2) oriented hexagonal wurtzite structure of the MFZO films, while the RTA process effectively improved its crystal quality. The intensity and full width at half maximum of the (0 0 2) peaks revealed that the MFZO films had the optimum crystallinity at the RTA time of 15–60 s and the largest grain size at the RTA time of 30 s. Under this optimal RTA condition, the electrical conductivity increased by 37%, reaching the optimum Hall mobility of 12.5 cm 2 /Vs, carrier concentration of 3.94 × 10 20 cm −3 , and resistivity of 1.27 × 10 −3 Ω cm. The average total transmittance in the visible region (380 – 780 nm) increased to more than 93% at the RTA duration of 15–60 s, and then decreased for a longer RTA time. The optical band gap, determined from the absorption edge of transmittance using Tauc plot, increased from 3.745 to 3.798 eV after RTA for 30 s. The figure of merit (FOM) of the MFZO film increased by 52% to 1.18 × 10 −2 Ω −1 . Thanks to the use of appropriate dopants and RTA process, this high FOM is much superior to previous research results on MFZO thin films with FOMs ranging from 10 −6 to 10 −3 Ω −1 . This work provides a fast and low-temperature approach to realize high-FOM MFZO thin films to fulfill the requirements of a transparent electrode in optoelectronic devices.

Progress in Sputter Growth of β‐Ga2O3 by Applying Pulsed‐Mode Operation

β‐Ga2O3 thin films are deposited by pulsed radio‐frequency (RF) magnetron sputtering on c‐sapphire substrates, using a stoichiometric Ga2O3 target and a constant gas flux of an argon–oxygen mixture. Pulsed sputtering offers a way to overcome the restrictions of conventional sputtering. The parameters RF power and pulse duty cycle (PDC) are varied systematically to optimize the synthesis of Ga2O3 thin films. Subsequently, the resulting as‐deposited (AD) Ga2O3 layers are analyzed in terms of structural and optical properties and the results are compared with those on the samples treated by postdeposition rapid thermal annealing. Based on this analysis, the process parameters are evaluated in terms of β‐Ga2O3 formation. Postdeposition temperature treatments are found to yield a better crystal quality. However, a strong interdiffusion with the Al2O3 substrate is observed. The optical bandgap of the sputtered thin films is found to be quite independent of the RF sputtering power but to depend strongly on the PDC used, whereas the layer thickness rather strongly increases with both of those growth parameters. These evolutions are assigned to changes in the energy and ionic species of the plasma. Traces of GaOx‐related phases in addition to β‐Ga2O3 are found in the interphase between the growing thin films and the underlying substrate.

Effect of rapid thermal annealing on structural and optical properties of ZnS thin films fabricated by RF magnetron sputtering technique

The ZnS thin films have been deposited by radio frequency magnetron sputtering at room temperature. Post-deposition rapid thermal annealing treatment was done for the films deposited at different powers ranging from 70 to 100 W. One peak is observed for as-deposited and annealed thin films at around 28.48° corresponding to the (111) reflection plane indicating a zincblende structure. The overall intensity of the peaks and the FWHM values of as-deposited films increased after annealing corresponding to the increase in crystallinity. The optical energy bandgap is found in the range of 3.24–3.32 eV. With increasing annealing temperature, the decrease in the Urbach energy values indicating a decrease in localized states which is in good agreement with the XRD results where the crystallinity increased. The surface morphology of the films seems to be composed of Nano-granules with a compact arrangement. Apparently, the grain size increases in the deposited films as annealing temperature increases. The compositional ratio attained close to the stoichiometric ratio of 1:1 after annealing. From the Hall effect measurement, the carrier concentration and mobility are found to increase after annealing. The high carrier concentration and mobility also comply with structural and optical analysis. Best results are found for the film annealed at 400 °C deposited at 90 W.

Thin-film light-addressable potentiometric sensor with SnOx as a photosensitive semiconductor

In this study, a tin-based oxide (SnOx) semiconductor layer on a commercial indium tin oxide (ITO)/glass substrate was investigated for the first time for use as the active layer of a light-addressable potentiometric sensor (LAPS). The photoabsorption of SnOx layers sputtered using varying Ar/O2 gas flow ratios was characterized by means of the ultraviolet–visible spectroscopy (UV–Vis); the photo/electric response of a LAPS directly covered with an NbOx sensing membrane was evaluated under modulated ultraviolet illumination. In situ substrate heating at 250 °C during sputtering and post-deposition rapid thermal annealing (RTA) with temperatures of 400 and 450 °C in a N2 environment were applied to study sample behavior. Based on X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results, the fabricated SnO2 layer can be transformed into a polycrystalline SnO2 phase in the bulk with a surface SnO layer by thermal budget. A high photocurrent and an acceptable pH sensitivity of 1.29 μA and 57.6 mV/pH, respectively, are obtained under UV light-emitting diode (LED) illumination for a LAPS built using a SnOx layer sputtered with a flow ratio of Ar/O2 = 46/4 with substrate heating at 250 °C. The stability and lifetime performance of the SnOx LAPS needs to be improved by further process optimization, especially in terms of developing a crack-free SnOx process and increasing sensing membrane coverage. The experimental results show the potential of SnOx for use as the active layer in a LAPS.

Negatively charged silicon nitride films for improved p-type silicon surface passivation by low-temperature rapid thermal annealing

The effect of post-deposition rapid thermal annealing (RTA) on p-type Czochralski silicon surface passivation by plasma-enhanced chemical vapor deposited nitrogen-rich silicon nitride (SiNx) films has been investigated. The effective carrier lifetime is significantly improved after annealing at low temperature (400 °C–450 °C) for 15–30 s. This improvement is associated with a decrease of N–H and Si–H bond densities in SiNx films and, a resultant decreased density of states at the SiNx/Si interface. More importantly, the polarity of fixed charges is converted from positive to negative in the annealed SiNx films. It is demonstrated that a release of hydrogen atoms to the SiNx/Si interface combined with a tuning of charges during low-temperature RTA, is very beneficial for p-type silicon surface passivation.

Characterization of Cuprous Oxide Thin Films for Application in Solar Cells

Cuprous oxide (Cu2O) has a high optical absorption coefficient and favourable electrical properties, which make Cu2O thin films attractive for photovoltaic applications. Using reactive radio-frequency magnetron sputtering, high quality Cu2O thin films with good carrier transport properties were prepared. This paper presents the characteristics of Cu2O thin films that were sputter deposited on quartz substrates and subjected to post-deposition rapid thermal annealing. The thickness of the thin films and the optical constants were determined by ellipsometry spectroscopy (SE). The optical transmittance increased in lower wavelength region after annealing at 900 ̊C in rapid thermal annealing (RTA). The structural and morphological properties of the Cu2O thin films were investigated by electronic scanning microscopy (SEM) and atomic force microscopy (AFM), whereas elemental analysis was performed by X-ray fluorescence spectroscopy (XRF). The carrier mobility, carrier density and film resistivity were changed after post-deposition rapid thermal annealing from respectively ~14 cm2/Vs, ~2.3 x 1015 cm-3 and ~193 Ωcm for the as-deposited Cu2O film to ~49 cm2/Vs, ~5.0 x 1014 cm-3 and ~218 Ωcm for the annealed Cu2O film. The investigation suggests that the sputter-deposited Cu2O thin films have good potential for application as absorber layers in solar cells.

Boosting highly transparent and conducting indium zinc oxide thin films through solution combustion synthesis: influence of rapid thermal annealing

IZO thin films with In:Zn ratio of 7:3 and 3:7 were prepared by solution combustion synthesis of metal oxide nitrates and influence of post-deposition rapid thermal annealing (RTA) was studied. Individual 0.5 M indium and zinc oxide precursor solutions were mixed in 7:3 and 3:7 compositions. XRD analysis showed IZO 7:3 composition has only cubic bixbyite In2O3 structure while IZO 3:7 composition showed both hexagonal wurtzite ZnO and cubic bixbyite In2O3 phases. SEM and AFM analysis showed low roughness for IZO 7:3, rms < 2 nm whereas for IZO 3:7 composition surface roughness was >22 nm due to phase segregation. UV/ViS/NIR analysis showed transparency range desirable of transparent conductors for both compositions. Post-deposition RTA treatment resulted in high conductivity single phase IZO 7:3 films. Segregation of phases enhanced carrier scattering resulting in decreased mobility for IZO 3:7 films. Best performing IZO films demonstrated low resistivity 7.66 × 10−3 Ohm cm and high carrier concentration 5.09 × 1019/cm3 after 10 min RTA at 600 °C. These results demonstrate combustion synthesis and RTA are successful for development of films with enhanced conductivity and transparency through low cost vacuum-free synthesis reducing indium content for applications in photovoltaic devices, flat panel displays and transparent electronics.

Effect of post deposition annealing and post metallization annealing on electrical and structural characteristics of Pd/Al2O3/6H-SiC MIS capacitors

PurposeAl2O3 used as gate dielectric enables exploitation of higher electric field capacity of SiC, improving capacitive coupling and memory retention in flash memories. Passivation of traps at interface and in bulk which causes serious threat is necessary for better performance. The purpose of this paper is to investigate the effect of post-deposition rapid thermal annealing (PDA) and post-metallization annealing (PMA) on the structural and electrical characteristics of Pd/Al2O3/6H-SiC capacitors.Design/methodology/approachAl2O3 film is deposited by ALD; PDA is performed by rapid thermal annealing (RTA) in N2 at 900°C for 1 min and PMA in forming gas for 10 and 40 min. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements data are studied in addition to capacitance-voltage (C-V) and current-voltage (I-V) characteristics for the fabricated Pd/Al2O3/SiC capacitors. Conduction mechanism contributing to the gate leakage current is extracted for the entire range of gate electric field.FindingsRTA forms aluminum silicide at the interface causing an increase in the density of the interface states and gate leakage current for devices with an annealed film, when compared with an as-deposited film. One order improvement in leakage current has been observed for the devices with RTA, after subjecting to PMA for 40 min, compared with those devices for which PMA was carried out for 10 min. Whereas, no improvement in leakage current has been observed for the devices on as-deposited film, even after subjecting to PMA for 40 min. Conduction mechanisms contributing to gate leakage current are extracted for the investigated Al2O3/SiC capacitors and are found to be trapfilled limit process at low-field regions; trapassisted tunneling in the mid-field regions and Fowler–Nordheim (FN) tunneling are dominating in high-field regions.Originality/valueThe effect of PDA and PMA on the structural and electrical characteristics of Pd/Al2O3/SiC capacitors suitable for flash memory applications is investigated in this paper.

Improving carrier transport in Cu2O thin films by rapid thermal annealing

Cuprous oxide (Cu2O) is a promising material for large scale photovoltaic applications. The efficiencies of thin film structures are, however, currently lower than those for structures based on Cu2O sheets, possibly due to their poorer transport properties. This study shows that post-deposition rapid thermal annealing (RTA) of Cu2O films is an effective approach for improving carrier transport in films prepared by reactive magnetron sputtering. The as-deposited Cu2O films were poly-crystalline, p-type, with weak near band edge (NBE) emission in photoluminescence spectra, a grain size of ~100 nm and a hole mobility of 2–18 cm2 V−1 s−1. Subsequent RTA (3 min) at a pressure of 50 Pa and temperatures of 600–1000 °C enhanced the NBE by 2–3 orders of magnitude, evidencing improved crystalline quality and reduction of non-radiative carrier recombination. Both grain size and hole mobility were increased considerably upon RTA, reaching values above 1 µm and up to 58 cm2 V−1 s−1, respectively, for films annealed at 900–1000 °C. These films also exhibited a resistivity of ~50–200 Ω cm, a hole concentration of ~1015 cm−3 at room temperature, and a transmittance above 80%.

Frequency dispersion and dielectric relaxation in postdeposition annealed high-κ erbium oxide metal–oxide–semiconductor capacitors

The origin of frequency dispersion in postdeposition rapid thermal and furnace annealing treated Pt/Er2O3/Si/Pt, metal–insulator–semiconductor–metal (MISM) structure is systematically investigated. The cause of frequency dispersion in Pt/Er2O3/Si/Pt, MISM structure is attributed to the dielectric relaxation in high-κ Er2O3, after suppressing the extrinsic effects such as parasitic, lossy interfacial layer, surface roughness, polysilicon depletion, quantum confinement, and oxide tunneling. Further, the Havrilian–Negami law is used to model the frequency dispersion in postdeposition rapid thermal and furnace annealing treated Pt/Er2O3/Si/Pt, MISM structure up to 250 kHz. It is suggested that to obtain an accurate capacitance value, the dissipation factor must be minimum for the MISM structure with nanometer scale oxides/insulators. Additionally, a methodology is proposed for simple and efficient correction of measured capacitance from capacitance–voltage and capacitance–frequency characteristics. Moreover, the flatband voltage shift/hysteresis, frequency dependent border traps are estimated ∼0.45 V, ∼3.35 × 1012 traps/cm2 and ∼0.18 V, ∼1.84 × 1012 traps/cm2 for postdeposition rapid thermal and furnace annealing treated Pt/Er2O3/Si/Pt, MISM structures, respectively. Therefore, postdeposition furnace annealing treatment is superior to achieve high-quality high-κ Er2O3 (κ ∼16), with low frequency dispersion of ∼9% up to 250 kHz and minimal hysteresis (∼0.18 V) for next-generation complementary metal–oxide–semiconductor technology.

Rapid Thermal Annealing for Solution Synthesis of Transparent Conducting Aluminum Zinc Oxide Thin Films

Transparent conducting oxide films with optimized dopant molar ratio have been prepared with limited pre- and postdeposition annealing duration of 10 min. Multiple aluminum zinc oxide (AZO) layers were spin-coated on ordinary glass substrates. The predeposition consolidation temperature and dopant molar ratio were optimized for electrical conductivity and optical transparency. Next, a group of films were deposited on Corning glass substrates from precursor solutions with the optimized dopant ratio, followed by postdeposition rapid thermal annealing (RTA) at different temperatures and in controlled environments. The lowest resistivity of 10.1 × 10−3 Ω cm was obtained for films receiving RTA at 600°C for 10 min each in vacuum then in N2-5%H2 environment, while resistivity of 20.3 × 10−3 Ω cm was obtained for films subjected to RTA directly in N2-5%H2. Optical measurements revealed average total transmittance of about 85% in the visible region. A direct allowed transition bandgap was determined based on the absorption edge with a value slightly above 3.0 eV, within the typical range for semiconductors. RTA resulted in desorption of oxygen with enhanced carrier concentration and crystallinity, which increased the carrier mobility with decreased bulk resistivity while maintaining the required optical transparency.

Influence of homo-buffer layers and post-deposition rapid thermal annealing upon atomic layer deposition grown ZnO at 100 °C with three-pulsed precursors per growth cycle

ZnO main epilayers are deposited with three-pulsed precursors in every growth cycle at 100°C on various thicknesses of 300°C-grown homo-buffer layers by atomic layer deposition (ALD) on sapphire substrate. Samples are treated without and with post-deposition rapid thermal annealing (RTA). Two different annealing temperatures 300 and 1000°C are utilized in the ambience of oxygen for 5 min. Extremely low background electron concentration 8.4×1014cm−3, high electron mobility 62.1cm2/V s, and pronounced enhancement of near bandgap edge photoluminescence (PL) are achieved for ZnO main epilayer with sufficient thickness of buffer layer (200 ALD cycles) and post-deposition RTA at 1000°C. Effective block and remove of thermally unstable mobile defects and other crystal lattice imperfections are the agents of quality promotion of ZnO thin film.

Superconducting Characteristics of NbN Films Deposited by Atomic Layer Deposition

A fabrication process for NbN films with a high transition temperature $(T_{C})$ of about 17 K was developed to realize NbN/AlN/NbN superconducting-tunnel-junction array particle detectors with a high operation temperature of >1 K and a high sensitivity by using atomic layer deposition (ALD). The source (precursor) of the NbN films was ( tert -butylimido)bis(diethylamino)niobium [C16H39N4Nb]. NbN films were deposited on M-plane sapphire wafers. A 50-nm-thick NbN film was deposited with a substrate temperature of about 570 K and exhibited a $(T_{C})$ of 12.35 K. To improve the superconducting properties of the NbN formed by ALD, a postdeposition rapid thermal annealing process was performed. The dependence of $(T_{C})$ , the surface morphology, and the crystallinity of the film on thermal annealing temperatures was evaluated.

Single-crystal hexagonal perovskite YAlO3 epitaxially on GaAs(111)A and (001) using atomic layer deposition

Hexagonal perovskite YAlO3 films were epitaxially grown on both GaAs(001) and GaAs(111)A substrates by utilizing sub-nano-laminated ALD-Y2O3/Al2O3 multilayers with a post-deposition rapid thermal annealing (RTA) to 900°C in He ambience. The c-axis of the YAlO3 films was aligned along the surface normal of GaAs(001) and GaAs(111)A substrates. Excellent crystallinity was evidenced by the pronounced thickness fringes and the narrow peak width of YAlO3(0004) θ-rocking scan ~0.026°, which is close to that of GaAs substrate peak ~0.01°, suggesting a high quality epitaxy despite a large lattice mismatch >6% between the substrates and the films. YAlO3 was found to be single domain as grown on GaAs(111)A but has two rotational domains on GaAs(001). The interfaces between YAlO3 and both GaAs(111)A and GaAs(001) remained atomically abrupt after 900°C RTA.

Physical and electrical properties of flash memory devices with nickel oxide(NiO2) charge trapping layer

In this study, we proposed a metal-oxide high-k-oxide-silicon (MOHOS) memory device using a nickel oxide film as the charge trapping layer, and studied the effect of post-deposition rapid thermal annealing (RTA) on the physical and electrical properties. The physical properties were investigated via multiple material analysis techniques such as X-ray diffraction and atomic force microscopy. The optimal annealing temperature for depositing the charge trapping layer was determined through a thorough investigation of the memory window, program/erase (P/E) cycle, crystalline structure, and material composition. Compared to the as-deposited NiO2 film, a MOHOS-type memory device annealed at 900 °C in a nitrogen atmosphere exhibited improved memory characteristics, in terms of a larger window in the capacitance-voltage hysteresis, better data retention (lower charge loss of 11%), faster program and erase cycles, and endurance characteristics (104 P/E cycles) without any significant drift in the flat band voltage. Therefore, the MOHOS memory device with a NiO2 trapping layer is a very promising candidate for future memory device applications.

Lead-free piezoelectrics: V3+ to V5+ ion conversion promoting the performances of V-doped Zinc Oxide

Vanadium doped ZnO (VZO) thin films were grown by RF magnetron sputtering, starting from a ZnO:V ceramic target. The crystal structure, chemical composition, electric and piezoelectric properties of the films were investigated either on the as-grown thin films or after a post-deposition rapid thermal annealing (RTA) treatment performed at 600 °C for different lengths of time (1 and 5 min) in an oxygen atmosphere. Substitutional doping of Zn2+ with V3+ and V5+ ions strongly deteriorated the hexagonal wurtzite ZnO structure of the as-grown thin films due to lattice distortion. The resulting slight amorphization led to a poor piezoelectric response and higher resistivity. After the RTA treatment, strong c-axis oriented VZO thin films were obtained, together with a partial conversion of the starting V3+ ions into V5+. The improvement of the crystal structure and the stronger polarity of both V3+ – O and V5+ – O chemical bonds, together with the corresponding easier rotation under the application of an external electric field, positively affected the piezoelectric response and increased conductivity. This was confirmed by closed-loop butterfly piezoelectric curves, by a maximum d33 piezoelectric coefficient of 85 pm·V−1, and also by ferroelectric switching domains with a well-defined polarization hysteresis curve, featuring a residual polarization of 12.5 μC∙cm−2.