Effects of gallium surfactant on AlN thin films by microwave plasma chemical vapor deposition

In this work, AlN films were grown using gallium (Ga) as surfactant on 4° off-axis 4H-SiC substrates via microwave plasma chemical vapor deposition (MPCVD). We have found that AlN growth rate can be greatly improved due to the catalytic effect of trimethyl-gallium (TMGa), but AlN crystal structure and composition are not affected. When the proportion of TMGa in gas phase was low, crystal quality of AlN can be improved and three-dimensional growth mode of AlN was enhanced with the increase of Ga source. When the proportion of TMGa in gas phase was high, two-dimensional growth mode of AlN was presented, with the increase of Ga source results in the deterioration of AlN crystal quality. Finally, employing a two-step growth approach, involving the initial growth of Ga-free AlN nucleation layer followed by Ga-assisted AlN growth, high quality of AlN film with flat surface was obtained and the full width at half maximum (FWHM) values of 415 nm AlN (002) and (102) planes were 465 and 597 arcsec.

Structural and magnetic properties of micropolycrystalline cobalt thin films fabricated by direct current magnetron sputtering

Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As the sputtering power increases from 15 to 60 W,the Co thin films transition from an amorphous to a polycrystalline state,accompanied by an increase in the intercrystal pore width.Simultaneously,the resistivity decreases from 276 to 99μΩ·cm,coercivity increases from 162 to 293 Oe,and in-plane magnetic aniso-tropy disappears.As the sputtering pressure decreases from 1.6 to 0.2 Pa,grain size significantly increases,resistivity significantly de-creases,and the coercivity significantly increases(from 67 to 280 Oe),which can be attributed to the increase in defect width.Corres-pondingly,a quantitative model for the coercivity of Co thin films was formulated.The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy,which is primarily attributable to increased microstress.

Ultrafast carrier dynamics in GeSn thin film based on time-resolved terahertz spectroscopy

We measure the time-resolved terahertz spectroscopy of GeSn thin film and studied the ultrafast dynamics of its photo-generated carriers.The experimental results show that there are photo-generated carriers in GeSn under femtosecond laser excitation at 2500 nm,and its pump-induced photoconductivity can be explained by the Drude–Smith model.The carrier recombination process is mainly dominated by defect-assisted Auger processes and defect capture.The firstand second-order recombination rates are obtained by the rate equation fitting,which are(2.6±1.1)×10^(-2)ps^(-1)and(6.6±1.8)×10^(-19)cm^(3)·ps^(-1),respectively.Meanwhile,we also obtain the diffusion length of photo-generated carriers in GeSn,which is about 0.4μm,and it changes with the pump delay time.These results are important for the GeSn-based infrared optoelectronic devices,and demonstrate that Ge Sn materials can be applied to high-speed optoelectronic detectors and other applications.

Annealing Temperature-Dependent Luminescence Color Coordination in Eu-Doped AlN Thin Films

AlN was used as a host material and doped with Eu grown on Si substrate by pulsed laser deposition (PLD) with low substrate temperature. The X-ray diffraction (XRD) data revealed the orientation and the composition of the thin film. The surface morphology was studied by scanning electron microscope (SEM). While raising the annealing temperatures from 300˚C to 900˚C, the emission was observed from AlN: Eu under excitation of 260 nm excitation. The photoluminescence (PL) was integrated over the visible light wavelength shifted from the blue to the red zone in the CIE 1931 chromaticity coordinates. The luminescence color coordination of AlN: Eu depending on the annealing temperatures guides the further study of Eu-doped nitrides manufacturing on white light emitting diode (LED) and full color LED devices.

Tuning of Optical Properties via Annealing of Bismuth Ferrite (BiFeO3) Thin Films

In this study we are reporting annealing induced optical properties of bismuth ferrite (BiFeO3) thin films deposited on glass substrate via spin coating at 5000 rpm. The structural, optical and surface morphology of BiFeO3 (BFO) thin films have been studied via X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Optical absorption (UV-Vis) and Photoluminescence (PL) spectroscopy. XRD spectra confirm annealing induced phase formation of BiFeO3 possessing a rhombohedral R3c structure. The films are dense and without cracks, although the presence of porosity in BFO/glass was observed. Moreover, optical absorption spectra indicate annealing induced effect on the energy band structure in comparison to pristine BiFeO3. It is observed that annealing effect shows an intense shift in the UV-Vis spectra as diffuse absorption together with the variation in the optical band gap. The evaluated optical band gap values are approximately equal to the bulk band gap value of BiFeO3.

Atomic layer deposition for nanoscale oxide semiconductor thin film transistors:review and outlook

Since the first report of amorphous In–Ga–Zn–O based thin film transistors,interest in oxide semiconductors has grown.They offer high mobility,low off-current,low process temperature,and wide flexibility for compositions and processes.Unfortunately,depositing oxide semiconductors using conventional processes like physical vapor deposition leads to problematic issues,especially for high-resolution displays and highly integrated memory devices.Conventional approaches have limited process flexibility and poor conformality on structured surfaces.Atomic layer deposition(ALD)is an advanced technique which can provide conformal,thickness-controlled,and high-quality thin film deposition.Accordingly,studies on ALD based oxide semiconductors have dramatically increased recently.Even so,the relationships between the film properties of ALD-oxide semiconductors and the main variables associated with deposition are still poorly understood,as are many issues related to applications.In this review,to introduce ALD-oxide semiconductors,we provide:(a)a brief summary of the history and importance of ALD-based oxide semiconductors in industry,(b)a discussion of the benefits of ALD for oxide semiconductor deposition(in-situ composition control in vertical distribution/vertical structure engineering/chemical reaction and film properties/insulator and interface engineering),and(c)an explanation of the challenging issues of scaling oxide semiconductors and ALD for industrial applications.This review provides valuable perspectives for researchers who have interest in semiconductor materials and electronic device applications,and the reasons ALD is important to applications of oxide semiconductors.

Homojunction structure amorphous oxide thin film transistors with ultra-high mobility

Amorphous oxide semiconductors(AOS)have unique advantages in transparent and flexible thin film transistors(TFTs)applications,compared to low-temperature polycrystalline-Si(LTPS).However,intrinsic AOS TFTs are difficult to obtain field-effect mobility(μFE)higher than LTPS(100 cm^(2)/(V·s)).Here,we design ZnAlSnO(ZATO)homojunction structure TFTs to obtainμFE=113.8 cm^(2)/(V·s).The device demonstrates optimized comprehensive electrical properties with an off-current of about1.5×10^(-11)A,a threshold voltage of–1.71 V,and a subthreshold swing of 0.372 V/dec.There are two kinds of gradient coupled in the homojunction active layer,which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility.Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

Corrosion characteristics of single-phase Mg-3Zn alloy thin film for biodegradable electronics

Biodegradable metals as electrodes, interconnectors, and device conductors are essential components in the emergence of transient electronics, either for passive implants or active electronic devices, especially in the fields of biomedical electronics. Magnesium and its alloys are strong candidates for biodegradable and implantable conducting materials because of their high conductivity and biocompatibility, in addition to their well-understood dissolution behavior. One critical drawback of Mg and its alloys is their considerably high dissolution rates originating from their low anodic potential, which disturbs the compatibility to biomedical applications. Herein, we introduce a single-phase thin film of a Mg-Zn binary alloy formed by sputtering, which enhances the corrosion resistance of the device electrode, and verify its applicability in biodegradable electronics. The formation of a homogeneous solid solution of single-phase Mg-3Zn was confirmed through X-ray diffraction and transmission electron microscopy. In addition, the dissolution behavior and chemistry was also investigated in various biological fluids by considering the effect of different ion species. Micro-tensile tests showed that the Mg-3Zn alloy electrode exhibited an enhanced yield strain and elongation in relation to a pure Mg electrode. Cell viability test revealed the high biocompatibility rate of the Mg-3Zn binary alloy thin film. Finally, the fabrication of a wireless heater demonstrated the integrability of biodegradable electrodes and highlighted the ability to prolong the lifecycle of thermotherapy-relevant electronics by enhancing the dissolution resistance of the Mg alloy.

The effects of radio frequency atmospheric pressure plasma and thermal treatment on the hydrogenation of TiO_(2) thin film

The effects of radio frequency(RF)atmospheric pressure(AP)He/H_(2)plasma and thermal treatment on the hydrogenation of TiO_(2)thin films were investigated and compared in this work.The color of the original TiO_(2)film changes from white to black after being hydrogenated in He/H_(2)plasma at160 W(gas temperature~381℃)within 5 min,while the color of the thermally treated TiO_(2)film did not change significantly even in pure H_(2)or He/H_(2)atmosphere with higher temperature(470℃)and longer time(30 min).This indicated that a more effective hydrogenation reaction happened through RF AP He/H_(2)plasma treatment than through pure H_(2)or He/H_(2)thermal treatment.The color change of TiO_(2)film was measured based on the Commission Internationale d’Eclairage L*a*b*color space system.Hydrogenated TiO_(2)film displayed improved visible light absorption with increased plasma power.The morphology of the cauliflower-like nanoparticles of the TiO_(2)film surface remained unchanged after plasma processing.X-ray photoelectron spectroscopy results showed that the contents of Ti3+species and Ti-OH bonds in the plasma-hydrogenated black TiO_(2)increased compared with those in the thermally treated TiO_(2).X-ray diffraction(XRD)patterns and Raman spectra indicated that plasma would destroy the crystal structure of the TiO_(2)surface layer,while thermal annealing would increase the overall crystallinity.The different trends of XRD and Raman spectra results suggested that plasma modification on the TiO_(2)surface layer is more drastic than on its inner layer,which was also consistent with transmission electron microscopy results.Optical emission spectra results suggest that numerous active species were generated during RF AP He/H_(2)plasma processing,while there were no peaks detected from thermal processing.A possible mechanism for the TiO_(2)hydrogenation process by plasma has been proposed.Numerous active species were generated in the bulk plasma region,accelerated in the sheath region,and bumped toward the TiO_(2)film,which will react with the TiO_(2)surface to form OVs and disordered layers.This leads to the tailoring of the band gap of black TiO_(2)and causes its light absorption to extend into the visible region.

XPS Study of Electroless Deposited Sb2Se3 Thin Films for Solar Cell Absorber Material

As a thin film solar cell absorber material, antimony selenide (Sb2Se3) has become a potential candidate recently because of its unique optical and electrical properties and easy fabrication method. X-ray photoelectron spectroscopy (XPS) was used to determine the stoichiometry and composition of electroless Sb2Se3 thin films using depth profile studies. The surface layers were analyzed nearly stoichiometric. But the abundant amount of antimony makes the inner layer electrically more conductive.

Depth Profile Study of Electroless Deposited Sb2S3 Thin Films Using XPS for Photovoltaic Applications

Sb2S3 has gained tremendous research recently for thin film solar cell absorber material because of their easy synthesis, unique electrical and optical properties. The stoichiometry and composition of electroless Sb2S3 thin films were analyzed using XPS depth profile studies. The surface layers were found nearly stoichiometric. On the other hand, the inner layer was rich in antimony composition making it more conductive electrically.

High Energy X-Ray Dosimetry Using(ZnO)_(0.2)(TeO_(2))_(0.8)Thin Film-based Real-time X-Ray Sensor

This study reports the dosimetric response of a(ZnO)_(0.2)(TeO_(2))_(0.8)thin film sensor irradiated with high-energy X-ray radiation at various doses.The spray pyrolysis method was used for the film deposition on soda-lime glass substrate using zinc acetate dehydrate and tellurium dioxide powder as the starting precursors.The structural and morphological properties of the film were determined.The I-V characteristics measurements were performed during irradiation with a 6 MV X-ray beam from a Linac.The results revealed that the XRD pattern of the AS-deposited thin film is non-crystalline(amorphous)in nature.The FESEM image shows the non-uniform shape of nanoparticles agglomerated separately,and the EDX spectrum shows the presence of Te,Zn,and O in the film.The I-V characteristics measurements indicate that the current density increases linearly with X-ray doses(0-250 cGy)for all applied voltages(1-6 V).The sensitivity of the thin film sensor has been found to be in the range of 0.37-0.94 mA/cm^(2)/Gy.The current-voltage measurement test for fading normalised in percentage to day 0 was found in the order of day 0>day 15>day 30>day 1>day 2.These results are expected to be beneficial for fabricating cheap and practical X-ray sensors.

Investigation of Sprayed Lu2O3 Thin Films Using XPS

Spray pyrolysis method was used to deposit Lutetium Oxide (Lu2O3) thin films using lutetium (III) chloride as source material and water as oxidizer. Annealing was carried out in argon atmosphere at 450°C for 60 minutes of the films. To investigate the composition and stoichiometry of sprayed as-deposited and annealed Lu2O3 thin films, depth profile studies using X-ray photoelectron spectroscopy (XPS) was done. Nearly stoichiometric was observed for both annealed and as-deposited films in inner and surface layers.

XPS Depth Profile Study of Sprayed Ga2O3 Thin Films

Ga2O3 thin films were fabricated by spray pyrolysis method using gallium acetylacetonate as source material and water as oxidizer. The films were annealed at 450°C for 60 minutes in argon atmosphere. X-ray photoelectron spectroscopy (XPS) depth profile studies were carried out to analyze the stoichiometry and composition of sprayed as-deposited and annealed Ga2O3 thin films. Surface layers and the inner layers of as-deposited and annealed films were found nearly stoichiometric.

Effect of concentration of cadmium sulfate solution on structural,optical and electric properties of Cd_(1-x)Zn_(x)S thin films

Cd_(1-x)Zn_(x)S thin films were deposited by chemical bath deposition(CBD)on the glass substrate to study the influence of cadmium sulfate concentration on the structural characteristics of the thin film.The SEM results show that the thin film surfaces under the cadmium sulfate concentration of 0.005 M exhibit better compactness and uniformity.The distribution diagrams of thin film elements illustrate the film growth rate changes on the trend of the increase,decrease,and increase with the increase of cadmium sulfate concentration.XRD studies exhibit the crystal structure of the film is the hexagonal phase,and there are obvious diffraction peaks and better crystallinity when the concentration is 0.005 M.Spectrophotometer test results demonstrate that the relationship between zinc content x and optical band gap value E_(g) can be expressed by the equation E_(g)(x)=0.59x^(2)+0.69x+2.43.Increasing the zinc content can increase the optical band gap,and the absorbance of the thin film can be improved by decreasing the cadmium sulfate concentration,however,all of them have good transmittance.At a concentration of 0.005 M,the thin film has good absorbance in the 300-800 nm range,80%transmittance,and band gap value of 3.24 eV,which is suitable for use as a buffer layer for solar cells.

Effect of initial precursor concentration on TiO_2 thin film nanostructures prepared by PCVD system

TiO2 thin film was prepared on Si substrate by plasma chemical vapor deposition （PCVD） system and the morphologies of ZiO2 thin film were controlled by adjusting the initial precursor concentration. As the initial titanium tetra-isopropoxide （TTIP） concentration increases in PCVD reactor, the shapes of TiO2 particles generated in PCVD reactor change from the spherical small-sized particles around 20 nm and spherical large-sized particles around 60 nm to aggregate particles around 100 nm. The TiO2 particles with different shapes deposit on the substrate and become the main building blocks of resulting TiO2 thin film. We observed the TiO2 thin film with smooth morphology at low initial TTIP concentration, granular morphology at medium initial TTIP concentration, and columnar morphology at high initial TTIP concentration. It is proposed that we can prepare the TiO2 thin film with controlled morphologies in one-step process just by adjusting the initial precursor concentration in PCVD .

Growth of HT-LiCoO2 thin films on Pt-metalized silicon substrates

Layered LiCoO2 （HT-LiCoO2） films were grown on Pt-metalized silicon （PMS） substrates and polished bulk nickel （PBN） substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [001] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [001] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45μA·h·cm^-2·μm^-1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.

Study on Physical Process of Surface Oxidation of Rare Earth-Transition Metal Amorphous Magneto-Optical Thin Films

By using surface effects(Auger electron spectroscopy,X-ray photoelectron spectroscopy,polar Kerr effect)and volume effects(magnetization,torque curve)the physical process of surface oxidation of rare earth-transition metal amorphous magneto-optical thin films was studied in this paper.The rare earth elements oxidize preferentially and rich at the film surface,and the transition metals deplete in oxidation layer.Fe_2O_3 in the surface oxidation layer contributes to the planar magnetization,and thereby the anomalous peak appears near 180° on the torque curves and the amplitude of the peaks is related to the depth of surface oxidation layers.The iron bonds to oxygen easier than the cobolt.RE-Co magneto-optieal thin films have good properties of resistance to oxidation and humidity.

Fabrication of Poly-Si Thin Film on Glass Substrate by Aluminum-induced Crystallization

Amorphous silicon （ a-Si ） thin films were deposited on glass substrate by PECVD, and polycrystalline silicon （ poly- Si ） thin films were prepared by aluminum- induced crystallization （ AlC ）. The effects of annealing temperature on the microstructure and morphology were investigated. The AlC poly-Si thin films were characterized by XRD, Raman and SEM. It is found that a-Si thin film has a amorphous structure after annealing at 400℃ for 20 min, a-Si films begin to crystallize after annealing at 450 ℃ for 20 min, and the crystallinity of a-Si thin films is enhanced obviously with the increment of annealing termperature.

Effect of La Doping on Microstructure and Ferroelectric Prop-erties of Bi_4Ti_3O_(12) Thin Films Prepared by Sol-gel Method

The Bi4Ti3Oi2 and Bi3.25La0.75Ti3O12 thin films were prepared on the Pt/Ti/SiO2/Si substrate using the sol-gel method. The effect of La doping on the microstructure and ferroelectric properties of Bi4Ti3O12 films were investigated. Both the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films exhibited typical bismuth layered perovskite structure. The 2Pr （remanent polarization） value of Bi3.25La0.75Ti3O12 thin films is 18.6 μC/cm^2, which is much larger than that of Bi4Ti3O12 thin films. And the Bi3.2eLa0.75Ti3O12 films show fatigue-free behavior, while the Bi4Ti3O12 thin films exhibit the fatigue problem. The mechanism of improvement of La doping was discussed.