Thermal Annealing In N2 Ambient Research Articles

Photoemission Study on Si and Ge Segregation on Al/Si0.8Ge0.2 Structures

We have demonstrated the formation of an ultrathin Si and Ge layer on an Al/Si0.8Ge0.2(111) structure caused by controlling the annealing condition. From the XPS characteristics, the annealing temperature, rather than the time, was found to be important in controlling the Si and Ge segregation. Also, by thermal annealing in N2 ambient, the segregated Ge on the Al/Si0.8Ge0.2 structure was found to be stable and resistant to oxidation due to the surface Al oxide layer and the segregated Si. We also found that Ge atoms were highly selectively segregated from the Al/Si0.8Ge0.2(111) structure below 500ºC. It was also found that Ge atoms could be selectively segregated from the Al/Si0.8Ge0.2(111) structure by rapid thermal annealing. The results will lead to the development of two-dimensional Ge crystals that are highly compatible with Si ultra-large-scale integration processing.

Effect of Chemical Treatment and Thermal Annealing in N2 Atmosphere on Copper Foil Surface for Graphene Growth by Direct-Liquid-Injection Chemical Vapor Deposition Process

Copper foils are widely used as a substrate for graphene grown by chemical vapor deposition method. The qualities of Cu foils can significantly affect the characters of resulting graphene films. Here, we systematically investigated the effects of chemical treatments and thermal annealing at high temperatures (890-950 °C) in N2 atmosphere. We then compared the graphene quality grown by direct liquid injection chemical vapor deposition (DLI-CVD) method with cyclohexane (C6H12) precursor on un-treated and treated Cu foil. We found that the chemical treatment conditions can improve surface morphology of the Cu foil. In addition, the annealing process at 920 °C for 10 min in N2 atmosphere can increase the grain size and lead to a favorable crystal orientation of (111) plane. Raman and microscopy analyses of the graphene film, show higher yields of monolayer graphene, while, at other annealing conditions and un-treated Cu foil, multilayer graphene is observed.

Characteristics of quantum-dot light-emitting diodes fabricated using a sputtered zinc tin oxide electron-transporting layer

Quantum-dot light-emitting diodes (QD-LEDs) with a sputtered zinc tin oxide (ZTO) electron-transporting layer (ETL) were studied. A ZTO after-deposition treatment process consisting of oxygen plasma treatment and thermal annealing was studied to improve the performance of the sputtered metal oxide ETL. The optical and electrical properties of the ZTO ETL could be controlled by adjusting the thermal annealing temperature. The best performing QD-LED was obtained by applying the oxygen plasma treatment and 250 °C thermal annealing in N2 atmosphere in sequence. The relation between the ZTO ETL properties and the device performance was explained by considering the roles of the band gap defect states. In this work, we provide a way to control the ZTO ETL properties and to improve the QD-LED device performance by applying an after-deposition treatment to the ZTO ETL.

Thermal stability of germanium-tin (GeSn) fins

We investigate the thermal stability of germanium-tin (Ge1−xSnx) fins under rapid thermal annealing in N2 ambient. The Ge1−xSnx fins were formed on a GeSn-on-insulator substrate and were found to be less thermally stable than blanket Ge1−xSnx films. The morphology change and material quality of the annealed Ge1−xSnx fin are investigated using scanning electron microscopy, Raman spectroscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. Obvious degradation of crystalline quality of the Ge0.96Sn0.04 fin was observed, and a thin Ge layer was formed on the SiO2 surface near the Ge0.96Sn0.04 fin region after 500 °C anneal. A model was proposed to explain the morphology change of the Ge0.96Sn0.04 fin.

Thin films of AgIn5(S/Se)8 prepared in a two stage process

AgIn5 (S/Se) 8 thin films were prepared by sequential chemical deposition of In2S3–Ag2Se stack films and post-deposition thermal annealing in N2 atmosphere. The formations of AgIn5S8−xSex alloy was achievable through the post-deposition treatment at 350 and 400 °C. X-ray diffraction and energy dispersive X-ray analyses were performed on the samples. The direct optical band gap value E g for the films was found to be as the order of 1.75 eV at room temperature. The photo-response measurements exhibited that AgIn5(S/Se)8 thin films are photoconductive and p-type electrical conductivity of 6.6 × 10−6 (Ω cm)−1 and thermoelectric power of +18 µV/K.

GeO2 decorated reduced graphene oxide as anode material of sodium ion battery

GeO2-reduced graphene oxide (RGO) composites were prepared by a simple freeze-drying method. After thermal annealing in N2 atmosphere at 450°C for 2hours, the composites were examined as anode materials of sodium ion batteries for the first time. Their morphology, structure and electrochemical performance were characterized by field-emission scanning electron microscopy, X-ray diffraction, N2 adsorption-desorption isotherm, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. A maximum specific capacity of 330mAhg−1 can be achieved after 50 galvanostatic charge-discharge cycles at a current density of 100mAg−1 by tuning the RGO content in the composites. Even after 650 cycles at a high current density of 1Ag−1, the specific capacity can still maintain at 153.7mAhg−1, demonstrating the excellent Na ion storage properties of the GeO2-RGO composites.

Highly reflective Ti/Ag/Pt contacts to p-GaN for high-efficiency GaN-based light-emitting diodes

The authors report highly efficient GaN-based light-emitting diodes (LEDs) fabricated with Ti/Ag/Pt reflective p-type contact. Compared with the reference Ni/Ag/Pt contact, Ti/Ag/Pt contact annealed at optimized thermal annealing condition produced low specific contact resistances of 5.7 × 10−4 Ω cm2, and good optical reflectivity of 88.4% at 450 nm. This is due to the generated interfacial Ti–O layer upon thermal annealing in N2 ambient, which suppress the excessive inter-diffusion between Ag and GaN layers. Consequently, the LEDs fabricated with Ti/Ag/Pt contacts showed 32.6% brighter light output power and nearly the same forward voltages as compared to the reference LEDs fabricated with Ni/Ag/Pt contacts.

Influence of p-GaN annealing on the optical and electrical properties of InGaN/GaN MQW LEDs

Optical and electrical properties of InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) annealed in pure O2 ambient (500°C) and pure N2 ambient (800°C) were systematically investigated. The temperature-dependent photoluminescence measurements showed that high-temperature thermal annealing in N2 ambient can induce indium clusters in InGaN MQWs. Although the deep traps induced by indium clusters can act as localized centers for carriers, there are many more dislocations out of the trap centers due to high-temperature annealing. As a result, the radiative efficiency of the sample annealed in N2 ambient was lower than that annealed in O2 ambient at room temperature. Electrical measurements demonstrated that the LEDs annealed in O2 ambient were featured by a lower forward voltage and there was an increase of ~41% in wall-plug efficiency at 20mA in comparison with the LEDs annealed in N2 ambient. It is thus concluded that activation of the Mg-doped p-GaN layer should be carried out at a low-temperature O2 ambient so as to obtain LEDs with better performance.

Control of Eu Luminescence Centers by Codoping of Mg and Si into Eu-Doped GaN

The effects of Mg and Si codoping on Eu luminescence properties have been investigated in Eu-doped GaN (GaN:Eu). The Mg codoping into GaN:Eu produced novel luminescence centers consisting of Eu and Mg, and increased photoluminescence (PL) intensity in Eu,Mg-codoped GaN (GaN:Eu,Mg). However, this increased PL intensity was quenched by thermal annealing in N2 ambient, which is due to activation of Mg acceptors. In GaN:Eu,Mg codoped additionally with Si (GaN:Eu,Mg,Si), on the other hand, the Eu–Mg centers disappeared, while an additional luminescence center appeared. Furthermore, the additional luminescence center showed no quenching under N2 annealing because Si donors compensated for the Mg acceptors in GaN. Thermal quenching of the luminescence center was also approximately half of that in GaN:Eu. These results indicate that the codoping with additional impurities in GaN:Eu is a powerful technique to control Eu luminescence centers for realization of improved device performance in red light-emitting diodes using GaN:Eu.

Comprehensive study of the surface morphology evolution induced by thermal annealing in single-crystalline ZnO Films and ZnO bulks

We report on the evolution of the surface morphology induced by thermal annealing in N2 ambient over a wide temperature range of 500–1200 °C in single-crystalline ZnO films and ZnO bulks. The surface morphology is seriously changed by the annealing temperature, and the evolution can be categorized into three regions: island growth, island agglomeration, and pit formation. Island growth at low temperatures below 700 °C, is ascribed to the atomic migration to reduce surface energy, which causes surface roughening. Island agglomeration at intermediate temperatures of 700–900 °C is ascribed to the migration and the evaporation of surface atoms, which causes surface flattening. Pit formation at high temperatures above 900 °C is ascribed to the atomic evaporation by high vapor pressure, which causes surface destruction. On the other hand, the bulk lattice is continuously improved with increasing annealing temperature in the temperature regions before the surface-destruction region, which is attributed to the reduction in the numbers of point and line defects caused by recrystallization. As a result, the best surface morphology and the best bulk lattice are obtained at an annealing temperature of 900 °C. The common surface-morphology evolution of ZnO films and ZnO bulks with increasing annealing temperature can be summarized using the three steps of surface roughening by island growth, surface flattening by island agglomeration, and surface destruction by pit formation.

Eu^3+ reduction and efficient light emission in Eu_2O_3 films deposited on Si substrates

A stable Eu3+ → Eu2+ reduction is accomplished by thermal annealing in N2 ambient of Eu2O3 films deposited by magnetron sputtering on Si substrates. Transmission electron microscopy and x-ray diffraction measurements demonstrate the occurrence of a complex reactivity at the Eu2O3/Si interface, leading to the formation of Eu2+ silicates, characterized by a very strong (the measured external quantum efficiency is about 10%) and broad room temperature photoluminescence (PL) peak centered at 590 nm. This signal is much more efficient than the Eu3+ emission, mainly consisting of a sharp PL peak at 622 nm, observed in O2-annealed films, where the presence of a SiO2 layer at the Eu2O3/Si interface prevents Eu2+ formation.

Comparison of as-grown and annealed GaN/InGaN : Mg samples

Mg-doped InGaN was grown on unintentionally doped GaN layer, and Mg and defect behaviours in both GaN and InGaN : Mg were investigated through photoluminescence measurement at 7 K. Mg acceptor was found in unintentionally doped GaN after thermal annealing in N2 ambient, and Mg activation energy was estimated to be 200 meV and 110 meV for GaN and InGaN, respectively. Particularly, the ultraviolet band (3.0–3.2 eV) in the GaN layer was infrequently observed in the unannealed sample but quenched in the annealed sample; this band may be associated with oxygen-substituted nitrogen defects. Moreover, the measurement errors of photoluminescence and x-ray diffraction originated from strain were taken into account.

Threading dislocations annihilation in regrown GaN film on nanoporous GaN template

AbstractRegrowth of GaN buffer layer on nanoporous GaN at different chamber temperature of 750 °C, 850 °C and 1000 °C are used to study the mechanism behind threading dislocations reduction in the GaN film subsequently overgrown. The growth of a 100 nm GaN buffer layer at 850 °C causes dislocations to bend into the underlying GaN and annihilated at the interface of GaN buffer/nanoporous GaN. Thermal treatment of nanoporous GaN in MOCVD growth chamber at 850 °C in NH3 and N2 ambient leads to the pinning of the threading dislocations at its surface edge steps by impurity –vacancy complexes of SiNx. The SiNx are formed by the impinging adatoms of NH3 which interact with Si dangling bonds at the subgrain boundaries of the nanoporous Si‐doped GaN. When the nanoporous GaN sample undergoes rapid thermal annealing in N2 ambient, no effective filling of these voids are observed and dislocations density is not substantial reduced. Regrowth of GaN at 850 °C re‐structured the nanoporous GaN, forming a SiNx complex at the voids or pores which pinned dislocation propagation. This explained the mechanism behind dislocation annihilation in regrown GaN on nanoporous GaN template with the use of additional interfacial GaN buffer layer. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gd2O3 High-K gate dielectrics deposited by magnetron sputtering

Gd2O3 thin films as high-K gate dielectrics were deposited on Si substrates by magnetron sputtering at 550 °C and 13 Pa. X-ray diffraction and cross sectional high-resolution transmission electron microscopy studies revealed that the Gd2O3 film was crystalline and it was consisted of a mixture of cubic and monoclinic phases. And the film show preferential orientation growth: (111)cubic//(001)Si and (401)monoclinic//(001)Si. The Gd2O3 thin film presented acceptable electrical properties such as low leakage current density of 3.6×10-5 A/cm2 at +1 V with capacitance equivalent SiO2 thickness of 2.54 nm. Rapid thermal annealing in N2 atmosphere can passivate a large amount of oxygen vacancy and improve the electrical properties.

Ge nanocrystals in lanthanide-based Lu2O3 high-k dielectric for nonvolatile memory applications

Ge nanocrystals embedded in lanthanide-based high-k dielectric (amorphous Lu2O3 in this work) were formed using pulsed laser deposition followed by rapid thermal annealing in N2 ambient. The formation and evolution of the Ge nanocrystals have been studied using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) in conjunction with depth profiling, and secondary ion mass spectroscopy (SIMS) analysis. Plan-view TEM images indicated that the formation of nanocrystals was first initiated during the deposition process. The annealing treatment significantly enhanced the nucleation of Ge nanocrystals, resulting in a high areal density of 7×1011cm−2 Ge nanocrystals with a mean size of about 6nm in diameter in the amorphous Lu2O3 matrix. XPS depth profile analysis revealed that Ge nanocrystals were predominantly formed from the precipitation of Ge nuclei from the oxide phase. A low annealing temperature of 400°C was sufficient to dissociate the GeO2 and GeOx leading to the formation of Ge nanocrystals. An accumulation of Ge species close to the upper Ge∕Lu2O3 interface was observed from XPS and SIMS depth profile analysis. Different charge storage behaviors observed from the memory capacitor devices before and after annealing could be correlated to the changes in structure and composition of the film. The memory capacitor device fabricated from the annealed sample showed efficient charge storage effect under a low operation voltage without significant initial charge decay.

Formation of Ge Nanocrystals in Lu2O3 High-k Dielectric and its Application in Non-Volatile Memory Device

AbstractA simple technique for the formation of Ge nanocrystals embedded in amorphous Lu2O3 high-k dielectric was demonstrated by pulsed laser ablation followed by rapid thermal annealing in N2 ambient. The structure and composition of the Ge nanocrystals in the oxide matrix have been studied by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. A significant change in the structure and chemical composition of the film was obtained upon annealing. Cross-sectional and plan-view TEM images confirmed the formation of small Ge nanocrystals in amorphous Lu2O3 matrix with a mean size of about 6nm in diameter and a high areal density of 7 × 1011cm−2. The nanocrystals are well-isolated by the amorphous Lu2O3 in between, with almost spherical shape which are favorable for non-volatile memory (NVM) application due to an effective charge confinement. XPS measurements on the as-deposited sample indicate the existence of Ge in its oxidized state, consisting of GeO2 and Ge suboxides. A spontaneous reduction of GeO2 and GeOx was obtained after the annealing treatment, which provides Ge nuclei for nanocrystal formation. It is found that a low annealing temperature of 400oC is sufficient to dissociate the GeO2 and GeOx leading to the formation of Ge nanocrystals. The application of the nanocrystals in NVM devices was demonstrated by C-V characterization of the memory capacitor devices fabricated with Al2O3 control oxide layer. C-V results show a significant effect of the structure and composition of the film on the electrical performance of the device. The annealed device exhibits good memory behavior with a large memory window of 1.2V achieved with a low operation voltage.

Study of hydrogen stability in low-k dielectric films by ion beam techniques

With shrinking device geometries into the 65nm technology node, a transition to low-k dielectrics becomes increasingly attractive. Negative bias temperature instability, which is associated with hydrogen migration at elevated temperatures, becomes the main degradation mechanism of concern for conductivity breakdown in semiconductor devices. The possibility of hydrogen release during each of the fabrication process is, therefore, of great interest to the understanding of device reliability. In the current study, various low-k dielectric films were subjected to thermal annealing in N2 ambient at temperatures that are generally used for device fabrication. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) were used to investigate composition change and hydrogen redistribution of the dielectric films. The results indicate that organosilicate glass, silicon nitride and silicon oxynitride films were stable at temperatures up to 500°C. In phosphorus doped silicon glass and plasma-enhanced tetraethylorthosilicate films, significant hydrogen release from the surface region was evident after heat treatment in N2 purged environment at 300°C for 30min, further hydrogen release is observed as temperature increases.

Effect of rapid thermal annealing on the structure and magnetic properties of chemical vapor deposition cobalt layers

This paper presents the results obtained on cobalt layers after rapid thermal annealing in N2 ambient at temperatures between 525 and 800°C. The cobalt layers were deposited by chemical vapor deposition from Co(CO)3NO on to oxidized-Si substrates at 450°C. As the anneal temperature increases from 525to800°C the percentage layer resistivity decrease goes from 35% to 55%. The lowest resistivity achieved was ∼11μΩcm for 300-nm-thick layers and ∼14μΩcm for 180-nm layer annealed in the range of 650–800°C. XRD analysis shows that a mixture of fcc and hcp cobalt grains is present in the as-deposited material. As the annealing temperature increases the fcc Co peaks increase due to crystallization of the material. This was confirmed by surface and microstructure analysis using SEM and AFM. The grain size had significantly increased to 200–300nm ranges for both 180- and 300-nm layers. From the hysteresis loops it was found that the coercivity values are significantly reduced to 25Oe from 350 and 140Oe due to high-temperature annealing to give soft magnetic property.

Organic-Inorganic Hybrid Encapsulation for P3HT Field-Effect Transistors

AbstractWe investigated the effect of encapsulation on poly(3-hexylthiophe) (P3HT) bottom-gate field-effect transistors (BG-FETs) with a high on/off current ratio achieved by thermal annealing in N2 atmosphere. The intensity of the oxygen-related absorption peak in the Fourier-transform infrared (FT-IR) spectra of the P3HT films showed a correlation to the on/off current ratio of the FETs. In order to eliminate this oxygen-doping effect, we evaluated three types of encapsulation film: polymer insulator, SiNx, and polymer-SiNx hybrid insulator. We found that the polymer-SiNx hybrid insulator film can suppress both damage caused by the formation of the encapsulation layer and the doping caused by exposure to air. To investigate the effect of encapsulation, we calculated the time dependence of the unintentional dopant density of the P3HT film.

Study of TiW/Au Thin Films Metallization Stack for High Temperature and Harsh Environment Devices on 6H Silicon Carbide

Study of TiW/Au Thin Films Metallization Stack for High Temperature and Harsh Environment Devices on 6H Silicon Carbide