Plasma-assisted Pulsed Laser Deposition Research Articles

Plasma assisted pulsed laser deposition of WO3 films for thermochromism

Tungsten trioxide (WO3) is one of the extensively investigated transition metal oxides. Its excellent chromogenic properties make WO3 promising for a variety of scientific and technological applications. We report a new method for reactively depositing WO3 films by plasma assisted pulsed laser deposition that combines electron cyclotron resonance microwave discharge and pulsed laser ablation. The plasma formed during film deposition was spectroscopically characterized by optical emission measurement, revealing that the plasma contains high density of reactive gaseous oxygen and tungsten species which are essential for efficiently synthesizing WOx precursors and depositing WO3 films. The structure of the deposited films and the effect of post-deposition thermal annealing on the film structure were characterized by X-ray diffraction and Raman spectroscopy. The as-deposited WO3 film appears amorphous in nature. Annealing resulted in the growth of crystalline grains and the improvement in the crystallinity of monoclinic WO3. Optical properties of the prepared WO3 films were studied by measuring ultraviolet–visible–near infrared transmission spectra. With the increase of annealing temperature, the WO3 films show a continuous change in color, decline in transmittance, red shift in absorption edge, and narrowing in band gap, clearly manifesting the thermochromic features of the deposited WO3 films.

Effect of Oxygen Plasma on β-Ga2O3 Deep Ultraviolet Photodetectors Fabricated by Plasma-Assisted Pulsed Laser Deposition

We fabricated metal–semiconductor–metal-structured β-Ga2O3 photodetectors using a plasma-assisted pulsed laser deposition system with various oxygen plasma radio frequency (RF) powers ranging from 0 to 100 W. All optoelectronic properties of the material were enhanced as the RF power increased. β-Ga2O3 photodetector with RF power of 100 W showed the best optoelectronic characteristics, such as photoresponsivity of 0.39 A/W, external quantum efficiency of 192.61%, and detectivity of 9.09 × 1013 cm Hz1/2/W. In addition, photo-switching analysis revealed the fastest photoresponse speeds (1.46 and 0.21 s) for on/off switching. These results originate from the decrease in the oxygen vacancy defect concentration in the β-Ga2O3 films by the oxygen RF power. Our results suggest that β-Ga2O3 photodetectors fabricated with oxygen plasma can optimize and improve the photodetection performance and can be applied for future deep ultraviolet detectors.

Spatially resolved Raman piezospectroscopy for nondestructive evaluation of residual stress in β-Ga2O3 films

In this paper, the piezospectroscopic effect for β-Ga2O3, i.e. the spectral band shift in response to strain/stress, has been calibrated by the indentation method using spatially resolved Raman spectroscopy for quantitative stress evaluation of Ga2O3 devices, taking advantage of the crack-tip tensile stress field and the spatial probe deconvolution. A series of Vickers indentation prints were introduced on (010) and () Ga2O3 single crystals, and the relationships between observed band shifts and residual stresses were clarified to determine the phonon deformation potentials of the Raman bands. Accordingly, a quantitative analysis of the residual stress field in a Ga2O3 thin film grown on (0001) sapphire by plasma-assisted pulsed laser deposition, which revealed the presence of a gradient of incompletely released stress in the depth direction of the film, is shown as an example.

Dry Synthesis of Binder-Free Ruthenium Nitride-Coated Carbon Nanotubes as a Flexible Supercapacitor Electrode.

Ruthenium nitride was successfully deposited on a multiwalled carbon nanotube (MWCNT) forest grown on a stainless-steel mesh substrate by radiofrequency plasma-assisted pulsed laser deposition. This novel dry fabrication method for flexible supercapacitor electrodes eliminates toxic byproducts and the need for any binder component. Experimental results show a successful thin film coating of the individual MWCNTs with RuNx under various synthesis conditions. The electrochemical characterization demonstrates a significant improvement in capacitance of the synthesized RuNx-MWCNT electrode compared to the bare MWCNT forest, with a large potential window of 1.2 V. Capacitance values as high as 818.2 F g-1 (37.9 mF cm-2) have been achieved.

Nitrogen diffusion in zinc oxide

Nitrogen migration in ZnO was investigated by nitrogen isotope diffusion. The samples were deposited using plasma-assisted pulsed laser deposition. Nitrogen concentration depth profiles were obtained from secondary-ion-mass spectrometry measurements, and in gas effusion measurements, the molecular nitrogen flux was measured as a function of the heating rate. Measurements performed on sample stacks that were doped with isotopically enriched 15N and 14N in the top and bottom half of the samples, respectively, clearly demonstrate that nitrogen diffusion is governed by atomic diffusion and molecules are formed primarily at the sample surface. At high nitrogen concentrations, the diffusion coefficient, D, is thermally activated, while for low concentration diffusion, D is independent of temperature. The data can be described by a model, where N diffusion occurs between minimum energy positions by surmounting the barrier between sites at a saddle point. Separated in energy from the transport sites are deep levels with a concentration of ≈1018 cm−3. For high-concentration diffusion, the N chemical potential, μN, resides at ≈1.36 eV below the migration saddle point. For low concentration diffusion, μN shifts deeper in energy with a rate of ≈2.8 meV/K as the temperature increases. From N effusion data, the nitrogen density-of-states is derived. For high N concentration diffusion, two peaks are observed at ES–μN = −0.93 and −1.26 eV, while for low N concentration diffusion, a prominent peak at ES–μN = −1.63 eV occurs. Applying density functional theory calculations, different microscopic diffusion mechanisms are evaluated, and the corresponding transition states are derived.

Hydrogen density-of-states distribution in β-Ga2O3

Hydrogen bonding in β-Ga2O2 is investigated using hydrogen effusion measurements. The samples were grown by plasma-assisted pulsed laser deposition. With increasing deposition temperature, the total H concentration decreases from 8.1 × 1019 to 9.2 × 1018 cm−3. The dependence of the hydrogen chemical potential, μH, on the H concentration is derived from the effusion spectra and subsequently used to determine the H density-of-states distribution. β-Ga2O2 deposited at Tdep ≤ 723 K exhibits a needle-like peak in the H density-of-states distribution at ≈1.8 eV below the H transport states. With increasing Tdep, the H density-of-states changes and two broad peaks emerge that are located at ≈1.7 and 2.4 eV below the H transport states for Tdep ≥ 873 K.

Low temperature growth of In2O3 films via pulsed laser deposition with oxygen plasma

In2O3 films were deposited on c-plane sapphire substrates by using pulsed laser deposition (PLD) without and with oxygen plasma at various growth temperature. The crystal structure, optical properties and surface morphologies were determined by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometer and atomic force microscope. XRD analysis revealed that all films have the body-centered cubic structure with a preferable (222) orientation. The results of XRC, Raman spectroscopy and spectrophotometer prove the superiority of plasma-assisted PLD. The low temperature growth of crystal In2O3 film paves the way to be compatible with the established silicon microfabrication processes.

Epitaxial growth of (AlxGa1−x)2O3 thin films on sapphire substrates by plasma assisted pulsed laser deposition

(AlxGa1−x)2O3 was grown on a-plane sapphire substrates at 500 °C by plasma assisted pulsed laser deposition (PLD) in the whole Al concentration range. The films were characterized using x-ray photoelectron spectroscopy (XPS), x-ray diffraction, atomic force microscopy, and spectrophotometry. By using XPS to measure the bandgap of the films, it was found that as the Al concentration x changes from 0.00 to 1.00, the bandgap ranges from 5.3 to 8.5 eV. The results show that plasma assisted PLD is a promising method to grow ultra-wide bandgap (AlxGa1−x)2O3 at low temperatures, which paves the way for the application of power devices and other functional devices based on (AlxGa1−x)2O3.

Black titanium oxynitride thin films prepared by nitrogen plasma-assisted pulsed laser deposition for flat-panel displays

Preference for a classy black turn-off appearance and for distinct dark colors on flat-panel displays has led to a high demand for optically black materials. Titanium oxynitrides and tungsten-doped oxynitrides were prepared using nitrogen plasma assisted pulsed laser deposition, and their optical absorption properties were investigated. A selection of Ti-O-N films were prepared with different compositions by controlling the emission current (Ie) and discharge voltage (Vd) of the ion source. It was found that the nitrogen content of the Ti(O,N)x could be adjusted by controlling the Ie. The large, flat absorption coefficient of approximately 40 μm−1 in the visible range (400–700 nm) attained for the samples deposited at high Vd was attributed to tungsten doping from a W filament in the ion source. The 4.1 mol%W-doped Ti(O,N)x, which had a rock-salt-type structure, was optically jet-black. The origin of the flat wavelength dispersion in the W-doped Ti(O,N)x was attributed to the coexistence of semiconducting absorption and metallic absorption mechanisms. DFT calculations suggest that the 5d states achieved when using doped tungsten provide high absorption in the mid-wavelength range, whereas undoped-Ti(O,N)x was characterized by weak absorption.

Enhanced magnetic properties of amorphous FeGaN film growth by plasma assisted pulsed laser deposition

The amorphous N-doped FeGa film were successfully deposited on Si (001) substrate using N2-plasma assisted pulsed laser deposition system at different temperatures. The enlarged saturation magnetization of FeGaN film has been investigated, which is higher than pure FeGa film under the same preparation condition. The optimal saturation magnetization of FeGaN film can reach up to 300 emu/cc, which also can be tuned by controlling the N2 flux during the deposition process. With the increase of deposition temperature, the antiferromagnetic, ferromagnetic and paramagnetic characters have also appeared respectively. The reason can be attributed to the change of the short-range order of lattice structure of FeGaN.

Monatomic hydrogen diffusion in β-Ga2O3

The nature of hydrogen migration in β-Ga2O3 was investigated with respect to molecular or monatomic diffusion. For this purpose, β-Ga2O3 samples were grown by plasma-assisted pulsed laser deposition in which H and D were spatially separated. The samples were characterized using secondary-ion-mass spectrometry and hydrogen effusion measurements. The combination of these methods provides clear evidence for monatomic H and D diffusion in β-Ga2O3.

Growth properties of gallium oxide on sapphire substrate by plasma-assisted pulsed laser deposition

Gallium oxide was deposited on a c-plane sapphire substrate by oxygen plasma-assisted pulsed laser deposition (PLD). An oxygen radical was generated by an inductive coupled plasma source and the effect of radio frequency (RF) power on growth rate was investigated. A film grown with plasma assistance showed 2.7 times faster growth rate. X-ray diffraction and Raman spectroscopy analysis showed β-Ga2O3 films grown with plasma assistance at 500 °C. The roughness of the films decreased when the RF power of plasma treatment increased. Transmittance of these films was at least 80% and showed sharp absorption edge at 250 nm which was consistent with data previously reported.

Low temperature growth of Ga2O3 films on sapphire substrates by plasma assisted pulsed laser deposition

Monoclinic β-Ga2O3 thin films with (-201) orientation have been fabricated at substrate temperature as low as 200 °C by using plasma assisted pulsed laser deposition. The film showed high transmittance of over 80% with clear fringes in the wavelength range from 300 to 1000 nm. Structural characterization from X-ray diffraction as well as Raman spectra analysis demonstrated the monoclinic structure of the films. β-Ga2O3 film deposited at 200 °C showed similar growth rate as well as optical bandgap values with films grown at higher temperatures from 300 to 500 °C, indicating the enhanced reaction between Ga and oxygen species during the deposition process with the assistant of plasma at low temperature. The low temperature growth of β-Ga2O3 film paves the way to be compatible with the established lithography of semiconductor microfabrication processes.

(TiO2)1–x(TaON)x Solid Solution for Band Engineering of Anatase TiO2

Band engineering of anatase TiO2 was achieved by means of an anatase (TiO2)1–x(TaON)x (TTON) solid solution. Epitaxial thin films of TTON (0.1 ≤ x ≤ 0.9) were synthesized by nitrogen plasma-assisted pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. Epitaxial growth of anatase TTON was confirmed by X-ray diffraction. The lattice constants of the TTON thin films increased with TaON content in accordance with Vegard’s law, indicating formation of a complete solid solution. The bandgaps, band alignment, and refractive indices of the TTON thin films were investigated by combination of spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The bandgap of the anatase TTON systematically decreased with increasing x, mainly because of an upward shift in the valence band maximum caused by broadening of the valence band as a result of hybridization of the shallow N 2p orbital. The position of the conduction band minimum was rather insensitive to chemical composition, which makes the ban...

Optoelectrical Properties of a Heterojunction with Amorphous InGaZnO Film on n-Silicon Substrate

An a-IGZO/n-Si heterojunction device has been fabricated at room temperature by depositing amorphous InGaZnO (a-IGZO) film on n-type silicon substrate by plasma-assisted pulsed laser deposition and its optoelectrical properties studied in detail. The heterojunction showed distinct rectifying characteristic with rectification ratio of 1.93 × 103 at ±2 V bias and reverse leakage current density of 1.6 × 10−6 A cm−2 at −2 V bias. More interestingly, the heterojunction not only showed the characteristic of unbiased photoresponse, but could also detect either ultraviolet or ultraviolet–visible light by simply changing the polarity of the bias applied to the heterojunction. The variable photoresponse phenomenon and the charge transport mechanisms in the heterojunction are explained based on the energy band diagram of the heterojunction.

Study of aluminum nitride formation in a plasma with effect of double laser pulses on D16T aluminum alloy in air

In this paper, we propose new opportunities to increase the proportion of various aluminum ions in the near-surface laser plasma in the regimes of ablation of aluminum alloy surfaces by defocused double laser pulses, and AlN nanoclusters under the sequential influence of double pulses on the target (D16T aluminum alloy). Experimental results show that the intensity of the spectral lines of Al ions reaches a maximum when the time intervals between double pulses of the order of 5÷15 us, the pulse energy of 42 mJ (Al II) and 38 mJ (Al III); The percentage of AlN nanoclusters reaches a maximum at energy of pulses of about 40 mJ, defocus of 0 mm and number of pulses of 25÷30. Full Text: PDF References Zheng Biju and Hu Wen, "A novel loss compensation technique analysis and design for 60 GHz CMOS SPDT switch*", Journal of Semicond. 37, 063003 (2016). CrossRef Perez J.A., Vera I.P., Riascos H., Caicedo J.C., "Optical emission spectroscopy of Aluminum Nitride thin films deposited by Pulsed Laser Deposition", Jornal of Physics: Conference Series 511, 1 (2014). CrossRef D.-M. Marin, F. Stokker-Cheregi, M. Dumitru, V. Ion, M. Dinescu, "Aluminium nitride thin films grown by plasma assisted pulsed laser deposition", Romanian Reports in Physics 66, 1118 (2014). DirectLink L. T. Sukhov, Laser spectral analysis (Novosibirsk 1990). Kononenko T. V., Konov V. I., Lubnin E. N., Dausinger F., "Pulsed laser deposition of hard carbon coatings at atmospheric pressure", Quantum electronics 33, 189 (2003). CrossRef Goncharov V. K., Kozadaev K. V., "Formation of the condensed phase of metals exposed to submicrosecond laser pulses", Journal of Engineering physics 83, 80 (2010). CrossRef Fadaiyan A. R., Trinh Ngoc Hoang, Zazhogin A. P., Vestnik BSU 1, 27 (2011). Fadaian A. R., Zazhogin A. P., Vestnik BSU 1, 14 (2009). Kask N. E., Michurin S. V., Fedorov G. M., "Fractal structures in a laser plume", Kvant. electron. 33, 57 (2003). DirectLink Krainov V. P., Smirnov M. B., "???????? ??????? ????????? ??? ????????? ??????????????? ???????????? ????????? ????????" Uspekhi Fizicheskikh Hauk 170, 969 (2000). CrossRef Ilin ?.P., Root L.?., Journal of science of Siberia 1, 91 (2011). Herzberg G., Electronic spectra and structure of polyatomic molecules (Mir Press 1969).

Spectroscopic characterization of the plasmas formed during the deposition of ZnO and Al-doped ZnO films by plasma-assisted pulsed laser deposition

An oxygen-zinc plasma and an oxygen-zinc-aluminum plasma are formed by pulsed laser ablation of a Zn target or pulsed laser co-ablation of a Zn target and an Al target in an electron cyclotron resonance (ECR) discharge-generated oxygen plasma for the deposition of ZnO and Al-doped ZnO (AZO) films. The plasmas are characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy. Both the oxygen-zinc plasma and the oxygen-zinc-aluminum plasma contain excited species originally present in the working O2 gas and energetic species ablated from the targets. The optical emission of the oxygen-zinc-aluminum plasma is abundant in the emission bands of oxygen molecular ions and the emission lines of mono-atomic oxygen, zinc and aluminum atoms and atomic ions. The time-integrated spectra as well as the time-resolved spectra of the plasma emission indicate that the oxygen species in the ECR oxygen plasma experience additional excitation by the expanding ablation plumes, and the ablated species are excited frequently when traveling accompanying the plume expansion in the oxygen plasma, making the formed plasma highly excited and very reactive, which plays an important role in the reactive growth of ZnO matrix and the in-situ doping of Al into the growing ZnO matrix. The deposited ZnO and AZO films were evaluated for composition analysis by energy dispersive X-ray spectroscopy, structure characterization by X-ray diffraction and optical transmission measurement. The deposited ZnO is slightly rich in O. The Al concentration of the AZO films can be controlled and varied simply by changing the repetition rate of the laser used for Al target ablation. Both the ZnO and the AZO films are featured with hexagonal wurtzite crystal structure and exhibit high optical transparency in a wide spectral region. Al doping results in an improvement in the ultraviolet transparency, a blue shift in the absorption edge and a widening of the band gap.

Sapphire substrate-induced effects in VO2 thin films grown by oxygen plasma-assisted pulsed laser deposition

We investigate the structural and electronic properties of VO2 thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO2 film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO2, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO2 film growth with SMTs that can be easily tailored for device applications.

Composition and bandgap control of AlxGa1−xN films synthesized by plasma-assisted pulsed laser deposition

Ternary AlxGa1−xN films with different Al compositions were synthesized on sapphire and Si substrates by pulsed laser co-ablation of a polycrystalline GaAs target and a metallic Al target in nitrogen plasma generated by electron cyclotron resonance discharge of N2 gas.

Humidity sensors applicative characteristics of granularized and porous Bi2O3 thin films prepared by oxygen plasma-assisted pulsed laser deposition

Pulsed laser ablation of pure bismuth targets in a plasma discharge followed by thermal treatment as preparation method for humidity high-sensitive bismuth trioxide thin films deposited onto Si/Pt substrates were analyzed. Several thin films were deposited at different substrate temperatures during the pulsed laser deposition namely between 300°C and 600°C. Near to the electrical investigation, the structure and the morphology of the films as keys features for water adsorption are thoroughly investigated and correlated with their sensitivity as humidity sensors. Thus, it has been found that strong granularized Bi2O3 thin films obtained through oxygen plasma-assisted pulsed laser deposition onto Si/Pt substrate at 500°C provide the most interesting humidity sensing characteristics.