Optimization of pulsed laser deposited ZnO thin-film growth parameters for thin-film transistors (TFT) application

In this work we present the optimization of zinc oxide (ZnO) film properties for a thin-film transistor (TFT) application. Thin films, 50±10 nm, of ZnO were deposited by Pulsed Laser Deposition (PLD) under a variety of growth conditions. The oxygen pressure, laser fluence, substrate temperature and annealing conditions were varied as a part of this study. Mobility and carrier concentration were the focus of the optimization. While room-temperature ZnO growths followed by air and oxygen annealing showed improvement in the (002) phase formation with a carrier concentration in the order of 10¹⁷–10¹⁸/cm³ with low mobility in the range of 0.01–0.1 cm²/V?s, a Hall mobility of 8 cm²/V?s and a carrier concentration of 5×10¹⁴/cm³ have been achieved on a relatively low temperature growth (250 °C) of ZnO. The low carrier concentration indicates that the number of defects have been reduced by a magnitude of nearly a 1000 as compared to the room-temperature annealed growths. Also, it was very clearly seen that for the (002) oriented films of ZnO a high mobility film is achieved.     

Effect of annealing on contact performance and electrical properties of p-type high purity germanium single crystal

Van de Pauw Hall measurement is an effective method to characterize the properties of semiconductors, such as bulk concentration, mobility, and resistivity, all of which are used to describe the purity level in the semiconductors. However, the performance of the ohmic contacts has a direct impact on the reliability and accuracy of the results obtained from the Van de Pauw Hall measurement. In the present work, the influences of different annealing techniques on the performance of the InSn ohmic contacts have been investigated using a High Purity Germanium (HPGe) crystal sample. The results show that the preferred annealing condition is at 400 °C for 1 hour, which has provided a significant improvement of the InSn contact quality and microscopic homogenization of the impurities in the HPGe crystal. The carrier concentration, charge mobility, and resistivity of the sample annealed at 400 °C for 1 hour are 5.772×10¹⁰/cm³, 1.883×10⁴× cm²/Vs, and 5.795×10³×Ω?cm at 77 K, respectively.     

Activation of Al2O3 passivation layers on silicon by microwave annealing

Thin aluminum oxide layers deposited on silicon by thermal atomic layer deposition can be used to reduce the electronic recombination losses by passivating the silicon surfaces. To activate the full passivation ability of such layers, a post-deposition annealing step at moderate temperatures (≈400 ^°C, duration≈30 min) is required. Such an annealing step is commonly done in an oven in air, nitrogen, or forming gas atmosphere. In this work, we investigate the ability to reduce the duration of the annealing step by heating the silicon wafer with a microwave source. The annealing time is significantly reduced to durations below 1 min while achieving effective minority carrier lifetimes similar or higher to that of conventionally oven-annealed samples.     

Fabrication of nanopatterned sapphire substrates by annealing of patterned Al thin films by Laser Interference Lithography

Nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Square-patterned Al thin films with the diagonal length of 600 nm, period of 1 um and height of ～200 nm were obtained by the Laser Interference Lithography and Reactive Ion Etching. Patterned Al thin films were subsequently subjected to dual stage annealing due to the melting temperature of Al thin films (660 ^°C). The first comprised a low temperature oxidation anneal. The hillocks formation on Al thin films was minimized with an oxidation annealing at 450 ^°C for 24 h. The little change in the morphology of patterned Al thin films was observed at 450 ^°C for 24 h. This was followed by a high temperature annealing to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results show the patterns were retained on sapphire substrates after high temperature annealing at less than 1200 ^°C. The XRD and Raman results reveal that the orientation of island patterns by dual stage annealing of patterned Al thin films for 24 h at 450 ^°C, and 1 h at 1000 ^°C, was the same as that of the sapphire (0001) substrates.     

Impurity redistribution during laser irradiation in ion implanted silicon

(100) Silicon wafers implanted with 2 × 10^{15 31}P+/cm² at 100 keV have been annealed using a scanning beam of incoherent light. The main results obtained after annealing are: (a) the carrier concentration profile shows a complete dopant activation without diffusion of the implanted ions; (b) the values of carrier mobility are similar to those obtained by furnace annealing; (c) an improvement of minority carrier diffusion length is often observed; (d) a very good damage recovery is obtained. Transmission Electron Microscopy observations show that the residual damage is confined within a region at 0.2 μm depth and consists of dislocation loops of about 50 Å diameter. It is concluded that this technique can be used to obtain very good annealing of implanted layers.     

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×10¹⁵ cm⁻² can be obtained for a gallium implantation of 10¹⁶ cm⁻² by laser annealing with an energy density of more than 1.0 J cm⁻². Although the peak carrier concentration was found to be 8.0×10²⁰ cm⁻³, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm⁻². The annealing took place in the solid phase in this energy density range.     

Thermoluminescent dosimetric characteristics of annealed quartz

In the given present study, the effect of pre-irradiation heat treatment at 500 and 600 ^°C on the glow peaks of synthetic quartz was examined as a function of annealing time to obtain an optimum annealing procedure. It was observed that the annealing time is not a strongly sensitive parameter to change the intensities of glow peaks. On the other hand, the intensities of glow peaks between room temperature (RT) and 200 ^°C were continuously increased during successive readings after heat treatments. Moreover, the intensities of glow peaks above 250 ^°C have good stabilities. The obtained repeatability of a glow peak at ～320 ^°C over 10 cycles is within 5% after the application of annealing at 600 ^°C for 1 h. The general thermoluminescent dosimetric characteristics of synthetic quartz, such as the dose–response, signal fading as a function of storage time, and reusability were also tested using the annealing condition at 600 ^°C for 1 h. It was observed that dose-response behaviours of all glow peaks are similar to each other. They first follow linear part and then saturated at different dose levels. Peak 1 completely disappeared after 1 month storage in the dark room at RT. On the other hand, the intensity of peaks 2+3 was approximately reduced to 15% of its original value whereas the other peaks (P4–P5) were not sufficiently affected during this period.     

Fabrication and capacitive characteristics of conjugated polymer composite p-polyaniline/n-WO3 heterojunction

A nanocrystalline and porous p-polyaniline/n-WO₃ dissimilar heterojunction at ambient temperature is reported. The high-quality and well-reproducible conjugated polymer composite films have been fabricated by oxidative polymerization of anilinium ion on predeposited WO₃ thin film by chemical bath deposition followed by thermal annealing at 573 K for 1 h. Atomic force microscopy (AFM) analyses reveal a homogenous but irregular cluster of faceted spherically shaped grains with pores. The scanning electron microscopy confirms the porous network of grains, which is in good agreement with the AFM result. The optical absorption analysis of polyaniline/WO₃ hybrid films showed that direct optical transition exist in the photon energy range 3.50–4.00 eV with bandgap of 3.70 eV. The refractive index developed peak at 445 nm in the dispersion region while the high-frequency dielectric constant, ? _∞, and the carrier concentration to effective mass ratio, N/m^*, was found to be 1.58 and 1.10 × 10³⁹ cm^?3, respectively. The temperature dependence of electrical resistivity of the deposited films follows the semiconductor behavior while the C–V characteristics (Mott–Schottky plots) show that the flat band potential was ?791 and 830 meV/SCE for WO₃ and polyaniline.     

CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Evolution,migration and clustering of helium-vacancy complexes in RAFM steel- depth resolved positron annihilation Doppler broadening study

Indian Reduced Activation Ferritic Martensitic steel is implanted with 130 keV helium ions to a fluence of 5 × 10¹⁴ and 1 × 10¹⁶ ions/cm² and investigated using positron annihilation spectroscopy. The samples were characterised by defect sensitive S and W-parameters using depth resolved slow positron beam. A dose dependency is observed in the nucleation and growth of helium bubbles with annealing temperature. An experimental evidence for the migration of smaller helium-vacancy complexes is observed via the variation in thickness/width of irradiated layer with temperature. The S–W plot clearly shows the regions corresponding to defect annealing, bubble nucleation and growth.     

Effect of annealing time on the structural and ferromagnetic properties of the GaMnN thin films

GaMnN thin films were deposited on a sapphire (0001) substrate by using laser assisted molecular beam epitaxy. Subsequently, the samples were annealed in the ammonia ambience at 1000 °C for different time lengths. The crystalline quality was improved gradually, and the room temperature ferromagnetism of our samples becomes stronger with the increase of the annealing time within 25 min. The X-ray photoelectron spectra analysis confirmed that the Mn³⁺ concentration in the GaMnN films increased after annealing. The stronger ferromagnetism was observed in the sample with the higher Mn³⁺ concentration. However, too long annealing time, such as 35 min, will lead to the degradation of the crystalline quality and the decrease of Mn³⁺ concentration, which results in the weakened ferromagnetism. The optimal annealing time is 25 min at 1000 °C in our experiments. Finally, the origin of the room temperature ferromagnetism in our samples was discussed preliminarily.     

Channeling study of boron implanted silicon: Liquid nitrogen temperature implantation

Silicon samples have been boron implanted at 150 keV at liquid nitrogen temperature to a dose of 3.6 × 10¹⁵/cm². This dose rendered the implanted layer amorphous as viewed by helium ion backscattering. Four kinds of room temperature measurements were made on the same set of samples as a function of the isochronal annealing temperature. The measurements made were the determination of the substitutional boron content by the channeling technique using the B¹¹(p, α) nuclear reaction, observation of the disorder by helium ion backscattering, determination of the carrier concentration by van der Pauw Hall measurements, and the sheet resistivity by four point probe measurements. These measurements are compared with results from samples implanted at room temperature. The carrier concentration correlates well with the substitutional boron content for both room temperature and liquid nitrogen temperature implantations. Following annealing temperatures in the 600 to 800°C range, a much larger percentage of the boron lies on substitutional lattice sites, and therefore the carrier concentration is larger, if the implantation is done at liquid nitrogen temperature rather than at room temperature. Following liquid nitrogen temperature implantation, reverse annealing is observed from 600 to 800°C in the substitutional boron content, carrier concentration and sheet resistivity. The boron is more than 90 per cent substitutional after annealing to 1100°C for both the room temperature and liquid nitrogen temperature implantations. The low temperature implantation produced a buried amorphous layer, and this layer was observed to regrow from both the surface and substrate sides at approximately equal rates.     

Gettering of implanted Au in MeV?C implanted Si

The gettering behavior of 1 MeV?C implantation induced defects for Au (1.5 MeV, 2.2×10¹⁵ cm^-2), implanted into FZ Si(111), has been investigated using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. The gettering efficiency of the C implanted layer has been studied as a function of C dose, annealing temperature and time. For a C dose of 2×10¹⁶ cm^-2, a 2 h anneal at 950 °C has been found to result in a gettering efficiency going beyond ?90%. Thermal stability of the gettered Au in the C implanted layer has subsequently been investigated over a temperature range of 950–1150 °C using isochronal annealing. The gettered amount has been found to be stable up to 1050 °C beyond which there is a release. We have observed nanovoids in the C implanted layer surrounded by ?-SiC precipitates along with patches of a-SiC. Up to about 1050 °C, these nanovoids act as efficient gettering centers beyond which they seem to release the trapped Au. Four distinct regimes in annealing temperature with different mechanisms for Au gettering have been observed.     

Oxidation of bismuth nanodroplets deposit on GaAs substrate

Bismuth nanodroplets on GaAs substrate were obtained by metalorganic vapor phase epitaxy (MOVPE). New products have been synthesized when Bi nanodroplets are heated under oxygen atmosphere. The oxidation process of Bi nanodroplets consists of a heating from the room temperature to different oxidation temperatures (350, 500, 600 ^°C) with a temperature rate of 14 ^°C/min. The annealing duration was fixed to 30 min. The presence of oxygen in the products was confirmed by energy dispersive X-ray (EDX) measurements using a scanning electron microscope (SEM). SEM images show that Bi microcomposites density decrease and their size increases with increasing annealing temperature. After X-ray diffraction analysis of the products no obvious peaks could be observed. The reflectance spectra of the products were studied in spectral domains ranged from 200 nm to 1100 nm. By fitting the reflectivity signal, we extracted the thickness of the products and their refractive index variation versus wavelength. The results show that the thickness of the samples increases with increasing annealing temperature. The photoluminescence (PL) spectra under excitation at 325 nm shows a broad emission centered at around 1.92 eV.     

Effect of Al doping on structural,optical and electrical properties of SnO2 thin films synthesized by pulsed laser deposition

Aluminium-doped (Al = 0–5?wt.%) SnO₂ thin films with low-electrical resistivity and high optical transparency have been successfully synthesized by pulsed laser deposition technique at 500 °C. Structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated. X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content. The root mean square (R_q) surface roughness parameter, determined by atomic force microscopy decreases upon annealing of the as-deposited film. While resistivity of the film is the lowest (9.49 × 10^?4 Ω-cm) at a critical doping level of 1?wt.% Al, optical transparency is the highest (nearly 90%) in the as-deposited condition. Temperature dependence of the electrical resistivity suggests that the Mott’s variable range hopping process is the dominant carrier transport mechanism in the lower temperature range (40–135 K) for all the films whereas, thermally activated band conduction mechanism seems to account for conduction in the higher temperature region (200–300 K).     

Controlling magnetic properties of iron oxide nanoparticles using post-synthesis thermal treatment

Changes in morphological and magnetic properties of Fe₃O₄ nanoparticles before and after annealing are investigated in the present work. The nanoparticles are synthesized in a standard capacitively coupled plasma enhanced chemical vapour deposition system with two electrodes using ferrocene as the source compound. Post annealing, due to the sintering process, the particles fuse along with recrystallization. This results in increased size of the nanoparticles and the interparticle interaction, which play a major role in deciding the magnetic properties. X-ray diffraction patterns of the samples before and after annealing indicate a phase change from Fe₃O₄ to Fe₂O₃. Annealing at 200 ^°C causes the apparent saturation magnetization to increase from 6 emu?g^?1 to 15 emu?g^?1. When annealed at 500 ^°C, the magnetic properties of the nanoparticles resemble those of the bulk material. The evidence for the transition from a superparamagnetic state to a collective state is also observed when annealed at 500 ^°C. Variation of the magnetic relaxation data with annealing also reflects the change in the magnetic state brought about by the annealing. The correlation between annealing temperature and the magnetic properties can be used to obtain nanocrystallites of iron oxide with different sizes and magnetic properties.     

Effect of oxygen partial pressure and annealing on nanocrystalline p-type ZnO:Sb thin films

We have investigated the effect of oxygen partial pressure and annealing on nanocrystalline p-type Sb-doped ZnO thin films, grown by pulsed laser deposition, with hole concentration of 6.5 × 10¹⁸/cm³ and mobility of 53 cm²/V-s. Uses of higher working pressure or annealing are found to reduce carrier concentration. A strong correlation is observed between carrier concentration and the violet (3.02 eV) emission related to free Zn-vacancy; stronger the violet emission, smaller the carrier concentration. In contrast to earlier suggestion of using higher oxygen pressure for obtaining p-type conductivity, the present results show a deterioration of the quality of film.     

The transport properties of Dirac fermions in chemical vapour-deposited single-layer graphene

Abstract

The electronic transport properties of Dirac fermions in chemical vapour-deposited single-layer epitaxial graphene on anSiO₂/Si substrate have been investigated using the Shubnikov–de Haas (SdH) oscillations technique. The magnetoresistance measurements were performed in the temperature range between 1.8 and 43 K and at magnetic fields up to 11 T. The 2D carrier density and the Fermi energy have been determined from the period of the SdH oscillations. In addition, the in-plane effective mass as well as the quantum lifetime of 2D carriers have been calculated from the temperature and magnetic field dependences of the SdH oscillation amplitude. The sheet carrier density (1.42 × 10¹³ cm^?2 at 1.8 K), obtained from the low-field Hall Effect measurements, is larger than that of 2D carrier density (8.13 × 10¹² cm^?2). On the other hand, the magnetoresistance includes strong magnetic field dependent positive, non-oscillatory background magnetoresistance. The strong magnetic field dependence of the magnetoresistance and the differences between sheet carrier and 2D carrier density can be attributed to the 3D carriers between the graphene sheet and the SiO₂/Si substrate.     

Photoluminescence from Zinc Oxide Quantum Dots Embedded in Silicon Dioxide Matrices

ABSTRACT

ZnO quantum dots (QDs) embedded in SiO₂ matrix are fabricated by ion implantation and annealing treatment methods. When the Zn-doping dose is (2, 3, 5, and 7) × 10¹⁶ cm^?2, the size of quantum dots is in the range of ～4–10 nm in diameter according to the XRD and HR-TEM results. Ultraviolet and green light emissions from the specimen are obtained at room temperature. With the increase of the Zn-doping dose, the PL peak in the ultraviolet region red shifts from 3.32 to 3.10 eV. This PL peak is related to the size of ZnO QDs, which is ascribed to the free exciton recombination in QDs. The green light emissions centered at 2.43 and 2.25 eV are independent of the Zn-doping dose and annealing temperature, which are attributed to the deep-level defect and the small peroxy radical (SPR) defect, respectively.     

Influence of the annealing technique on the properties of Li ion-conductive Li1.3Al0.3Ti1.7(PO4)3 films

Li_1.3Al_0.3Ti_1.7(PO₄)₃ films were comparatively prepared by rapid thermal annealing (RTA) and conventional furnace annealing(CFA). The phase identification and surface morphology of the prepared films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical window, ionic conductivity, activation energy, and electronic conductivity were conducted by cyclic voltammetry, electrochemical impedance spectroscopy, and four-probe technique. The results show that the films prepared by RTA and CFA are homogenous and crack-free. The film prepared by RTA shows smaller grains and is denser than the one prepared by CFA. The electrochemical windows of the two films are beyond 2.4 V. The ionic conductivities of the films prepared by RTA and CFA are 2.7?×?10^?6 S cm^?1 and 1.4?×?10^?6 S cm^?1, respectively. The activation energy of the film prepared by RTA is 0.431 eV, which is slightly smaller than the one prepared by CFA. The electronic conductivity of the two films is about 10^?10 S cm^?1.