High-temperature Annealing In Oxygen Research Articles

Synthesis and Characterization of β-Ga2O3/por-GaAs/mono-GaAs Heterostructures for Enhanced Portable Solar Cells

This study comprehensively details the successful synthesis of a β-Ga2O3/por-GaAs/mono-GaAs heterostructure designed for portable solar cells. Employing a combination of electrochemical etching and high-temperature oxygen annealing, we engineered a heterostructure that exhibits both crystalline and amorphous phases. XRD, SEM, and Raman spectroscopy analyses confirmed the formation of crystalline β-Ga2O3 and GaAs, with the porosity in the GaAs layer enhancing light absorption and charge collection. The potential of the heterostructure to improve photovoltaic performance is attributed to the inherent stability of Ga2O3 and the increased surface area provided by the porous GaAs.

High temperature treatment of epitaxial nickel ferrite thin films: The way to bulk-like magnetic properties

An appropriate choice of growth conditions has made feasible fabrication of thin epitaxial NiFe2O4 / SrTiO3 films with parameters close to those of bulk nickel ferrite. Spin waves with a damping parameter as low as 10-2 and a very narrow ferromagnetic resonance line were observed in the samples subjected to post-growth high temperature annealing in oxygen. The analysis of electron and X-ray diffraction has shown substantial improvement of the crystalline quality of the annealed films. X-ray absorption spectroscopy and X-ray magnetic circular dichroism data simulation have revealed that the films exhibit a completely inverted spinel structure characterized by the maximal possible net magnetic moment.

Optical Anisotropy of SrTiO3(110) for Different Surface Terminations

In this work we investigate the SrTiO3(110) surface by reflectance anisotropy spectroscopy (RAS) at varying preparation steps including ex situ wet etching, high temperature oxygen annealing, as well as in situ vacuum annealing. Different surface terminations show distinctly different RAS spectra which are correlated to an altered surface stoichiometry measured by X‐ray photoelectron spectroscopy (XPS) and an altered valence band structure measured by UV‐photoelectron spectroscopy (UPS) in cases of conductive samples. We link the changes in the observed RAS spectra to various surface reconstructions, with particular focus of the signature of (3 × 1) and (1 × 4) reconstructed surfaces, and a metallic surface state observed in vacuum annealed SrTiO3.

Nanosecond X-ray detector based on high resistivity ZnO single crystal semiconductor

The pulse radiation detectors are sorely needed in the fields of nuclear reaction monitoring, material analysis, astronomy study, spacecraft navigation, and space communication. In this work, we demonstrate a nanosecond X-ray detector based on ZnO single crystal semiconductor, which emerges as a promising compound-semiconductor radiation detection material for its high radiation tolerance and advanced large-size bulk crystal growth technique. The resistivity of the ZnO single crystal is as high as 1013 Ω cm due to the compensation of the donor defects (VO) and acceptor defects (VZn and Oi) after high temperature annealing in oxygen. The photoconductive X-ray detector was fabricated using the high resistivity ZnO single crystal. The rise time and fall time of the detector to a 10 ps pulse electron beam are 0.8 ns and 3.3 ns, respectively, indicating great potential for ultrafast X-ray detection applications.

A diamond (1 0 0) surface with perfect phase purity

Diamond surfaces with (100) orientation and perfect phase purity regarding the coexistence of sp3 and sp2 bonding as well as near surface nitrogen implanted layers are repeatedly produced from one sample by a cycle of nitrogen implantation, etching in oxygen and wet chemical etching. Comprehensive surface studies carried out by X-ray photoelectron spectroscopy (XPS) involving a deconvolution of the C 1s peak into contributions of C sp3, C sp2 and C sp3(N) reveal the surface and near-surface phase and stoichiometry. It is demonstrated that efficient etching of nitrogen implanted diamond occurs by high temperature annealing in oxygen and a wet chemical treatment.

Reversible metal-insulator transition of Ar-irradiatedLaAlO3/SrTiO3interfaces

The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAlO3 (LAO) and SrTiO3, can be made completely insulating by low-energy, 150-eV, Ar+ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation.

Effective reduction of trap density at the Y2O3/Ge interface by rigorous high-temperature oxygen annealing

The impact of thermal post deposition annealing in oxygen at different temperatures on the Ge/Y2O3 interface is investigated using metal oxide semiconductor capacitors, where the yttrium oxide was grown by atomic layer deposition from tris(methylcyclopentadienyl)yttrium and H2O precursors on n-type (100)-Ge substrates. By performing in-situ X-ray photoelectron spectroscopy, the growth of GeO during the first cycles of ALD was proven and interface trap densities just below 1 × 1011 eV−1 cm−2 were achieved by oxygen annealing at high temperatures (550 °C–600 °C). The good interface quality is most likely driven by the growth of interfacial GeO2 and thermally stabilizing yttrium germanate.

Evolution of Vacancy-Type Defects, Phase Transition, and Intrinsic Ferromagnetism during Annealing of Nanocrystalline TiO2 Studied by Positron Annihilation Spectroscopy

The evolution of vacancy-type crystalline defects across the transition from anatase to rutile structure of titanium dioxide (TiO2) nanoparticles during high-temperature annealing in oxygen and argon is studied by using positron lifetime and coincidence Doppler broadening spectroscopic measurements. The TiO2 nanoparticles were synthesized through a simple sol–gel chemical route. The changes in the crystalline phase and lattice parameters of the nanoparticles upon thermal treatment were investigated by X-ray diffraction and high-resolution transmission electron microscopy, and the results were correlated with those of photoluminescence spectroscopy and positron annihilation measurements. The structural defects, mostly 3D vacancy clusters, in the nanoparticles were found to decrease in concentration during the annealing in O2 rather than in Ar at elevated temperatures. In the case of annealing in Ar, the vacancy-type defects persisted even at the highest annealing temperature of 900 °C used in the experimen...

Ir/n-ZnO Schottky Barrier Ultraviolet Photodiodes

ZnO Schottky barrier photodiodes (PDs) with Iridium (Ir) contact electrodes were fabricated in this study. We could reduce the reverse leakage current and improve the performance of ZnO ultraviolet (UV) PDs by using 500 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealing. This could be attributed to the formation of IrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> after thermal annealing. With -1 V applied bias, it was found that the reverse current for nonannealed and 500 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealed PDs were 4.46 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 9</sup> and 8.87 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> A, respectively. It was also found that we could enhance UV-to-visible rejection ratio, reduce noise level, and enhance the detectivity by high-temperature oxygen annealing.

Mechanism of Date Retention Improvement by High Temperature Annealing of Al2O3 Blocking Layer in Flash Memory Device

The mechanism underlying improved data retention via high-temperature oxygen annealing of the Al2O3 blocking layer in a charge-trap type flash memory device is investigated in comparison with the case of high-temperature nitrogen annealing. The results show that significant improvement of the retention property can be achieved by oxygen annealing at 1100 °C, compared to nitrogen annealing. Experimental evidence indicated that the underlying mechanism does not arise from suppression of the trap-assisted tunneling current through the blocking oxide; instead it is caused by a reduction of the thermionic emission component of the charge loss factor. This is possibly due to changes of the conduction band offset of the crystallized Al2O3.

Performance Improvement of HfAlOxN n-Channel Metal–Oxide–Semiconductor Field-Effect Transistors by Controlling the Bonding Configuration of Nitrogen Atoms Coordinated to Hf Atoms

A high-temperature oxygen annealing (HiTOA) process has been developed to recover the degradation of the electrical characteristics due to the nitrogen incorporation into the HfAlOx film. The HiTOA process was carried out after the introduction of the nitrogen atoms. This process affected the bonding configuration of the nitrogen atom coordinated to the hafnium atom, and reconverted the nitrogen atom into an oxygen one. Therefore, this substitution markedly recovered the gate leakage current through the HfAlOxN film with a slight increase in the equivalent oxide thickness. Additionally, it significantly improved the effective mobility of n+ polycrystalline silicon (poly-Si) gate n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs).

The effect of oxygen annealing on ZnO : Cu and ZnO : (Cu,Al) diluted magnetic semiconductors

Here we report a systematic study of magnetic, electronic and microstructural properties of Cu-doped and Cu and Al codoped ZnO thin films, grown epitaxially on a (0 0 0 1) sapphire substrate by the pulsed laser deposition technique. The films were annealed in oxygen at high temperature (600 °C) and their properties were compared with the as deposited films in order to study the role of defects like oxygen vacancies on the ferromagnetic properties. The doping of ZnO : Cu specimens with Al increased the carrier concentration by three orders of magnitude (from 1017 to 1020 cm−3) without altering the ferromagnetic ordering. On the other hand, a reduction in oxygen vacancies concentration brought about by high temperature annealing in oxygen had a large detrimental effect on ferromagnetism. These results tend to eliminate a free carrier mediated mechanism and point towards a defect mediated mechanism, such as a bound-magnetic-polaron mediated exchange, as being responsible for stabilizing long-range ferromagnetic ordering in these systems.

Schottky behavior at Ag/Nb-1.0 wt%-doped SrTiO 3 interface

In this work, Schottky junctions of Ag/Nb-1.0 wt%-doped SrTiO 3 (NSTO) have been fabricated by magnetic controlled sputtering technique and annealing process after sputtering. The junction between these two materials exhibits good Schottky rectifying behavior after high-temperature annealing, and the capacitance–voltage characteristics show linear C −2– V relationships in the reverse condition. The barrier heights were determined to be 2.75 eV or so by current–voltage and capacitance–voltage methods, respectively. I– V characteristics revealed that high-temperature annealing in oxygen at 700 °C alters this thin surface barrier, reduces the leakage current remarkably.

Poole-Frenkel conduction in Al/ZrO2 /SiO 2 /Si structures

Leakage currents through Al/ZrO2/SiO2/n-Si metal-insulator-semiconductor (MIS) capacitors were studied. Thin SiO2 films were chemically grown on monocrystalline phosphorous doped silicon wafers. Zirconia films with thicknesses of 15 and 50 nm were deposited by radio frequency (rf) magnetron sputtering and, then, annealed in oxygen ambient at 850 ○C, for 1 h. The dielectric constant of the sputtered and annealed ZrO2 layer was of about 17.8. The equivalent oxide thickness (EOT) of the stack 15 nm and 50 nm-ZrO2/SiO2 structure was estimated to be 3.2 nm and 10.7 nm, respectively. The temperature dependence of the leakage currents was explained by Poole-Frenkel (PF) conduction mechanism. Shallow trap levels in the studied structure of about 0.2 eV and 0.46 eV were calculated. The existence of A and D-defects, due to the sputtering and high temperature annealing in oxygen, was suggested.

Co-doped ZnO dilute magnetic semiconductor

This paper reports on recent findings in the Co-doped ZnO system where as-deposited samples with n-type semiconductor properties display magnetic ordering above room temperature. Detailed atomic scale structural characterization has eliminated clustering and second-phase formation as the source of the magnetic behavior. Upon high-temperature annealing in oxygen, the samples become insulating and the magnetization drops. This suggests that the observed magnetic behavior of the oxide is directly related to the presence of intrinsic defects, notably oxygen vacancies and Zn interstitials. These defects are believed to mediate exchange coupling of the Co spins through electron doping of the matrix, and perhaps also the formation of bound magnetic polarons.

Current transport and high-field reliability of aluminum/hafnium oxide/silicon structure

The current transport mechanisms and the charge trapping characteristics of HfO 2 gate dielectrics prepared by different annealing conditions were studied. We found that the large leakage currents are mostly associated with the high trap density in the dielectric films. Taking into account the ionic nature of the metal oxide, the phonon-assisted trap ionization model should be used to explain this behavior. For samples with high temperature annealing in oxygen, large barriers of over 2 eV were found from the Fowler–Nordheim plots. These values were attributed to the existence of an interface silicon oxide layer. The effective interface barrier is also governed by the bulk properties of HfO 2 film, which modifies the field strength in the interface oxide layer according to the Gauss law. The reliability of the gate dielectric can be improved by the formation of interface SiO 2 layer but stoichiometric improvement in the HfO 2 layer has an adverse effect on the stressing induced charge trapping due to the interface barrier lowering effect.

Advantages of HfAlON gate dielectric film for advanced low power CMOS application

There are a number of challenges against an actual employment of high-k films in the production, but ultra-thin SiON films cannot survive for low power application anymore. On the other hand, any new materials introduced into ULSI fabrication processes are required to be used for a couple of device generations, so the material selection should be carefully made. We have investigated HfAlON film as a high-k material in perspective of the equivalent oxide thickness (EOT)=1nm, and has newly developed a layer-by-layer deposition and annealing (LL-D&A) method for the film growth technique and a high temperature oxygen annealing (HiTOA) for the post-deposition annealing process, in order to overcome intrinsic challenges of deposited films. This paper describes recent progress of HfAlON gate stack technology, and discusses advantages of those approaches for advanced low power CMOS from scalability viewpoints of material and film growth technique as well as from experimental results of gate leakage current reduction, mobility improvement and threshold voltage control.

Annealing effects on the microstructure and properties of Y(Ni,Mn)O 3 thin films

Epitaxially c-axis oriented thin films of YNi x Mn 1− x O 3 (YNMO), x = 0.33 and 0.5, were grown on (1 0 0) SrTiO 3 substrates by pulsed laser-ablated deposition technique. High temperature oxygen annealing shows a large improvement in the ferromagnetic transition temperature T c for the film with x(Ni) = 0.33 while only a slight increase in T c occurs for the x(Ni) = 0.5 film. We suggest that such increase in T c is largely associated with microstructural changes induced by the thermal annealing. In order to optimize the magnetic properties of the YNMO films, it is necessary to control the initial growth conditions so as to have a microstructure of well-connected grains of uniform size.

Ultra violet photoluminescenc of ZnO films on different substrates

Polycrystalline ZnO films with a good preferred orientation were deposited on sapphire, Si and quartz substrates by rf magnetron sputtering. A 356 nm Ultraviolet (UV) photoluminescence (PL) peak and a 446 nm blue peak were observed at room temperature when excited with 270 nm light. After high-temperature annealing in oxygen, the crystallinity of the films was improved. The intensity of the UV emission increased by 7 and 14 times, respectively, for the films on sapphire and quartz substrates respectively. We conclude that the UV emission originates from the inter-band transition of electrons and the blue emission is due to the transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.

The origin of radiation instability in yttrium-ion-doped lead tungstate crystals

Abstract Some Y3+-doped PbWO4 (PWO:Y3+) crystals grown by the modified Bridgman method showed exceptional behaviours, namely the increase in the light yield after low-dose-rate irradiation and also the improvement in the optical transmission at around 430 nm. In this paper, we studied the influences of high-temperature annealing in an oxygen-rich atmosphere on the stability of scintillation properties and radiation hardness of PWO: Y3+. The results show that annealing in oxygen enhances the absorption band at around 430 nm and makes optical transmission unstable at this wavelength after irradiation. After high-temperature annealing, the radiation-induced absorption coefficient is also negative around 430 nm. The 430 nm absorption band introduced by high-temperature annealing in oxygen has the same characteristics as the pre-existing bands in as-grown PWO: Y3+ crystals. So it decreases the stability of scintillation properties and radiation hardness of PWO: Y3+ crystals. The radiation instability relates t...