Plasma-enhanced Pulsed Laser Deposition Research Articles

Comparative study on the dynamics and the composition between a pulsed laser deposition (PLD) and a plasma enhanced PLD (PE-PLD)

We report the effect of single and dual radio frequency (RF) plasma discharge on the composition and dynamics of a titanium plasma plume produced in a plasma-enhanced pulsed laser deposition (PE-PLD) system. The study was carried out in a nitrogen environment at different pressures. Time-resolved images, optical emission spectroscopy, and interferometry were employed to analyze the plasma. We were able to fit time-resolved images using different expansion models, obtained an expansion velocity between 6 and 30 × 103 m/s. Emission lines from N II, Ti II, were observed by changing the pressure and RF conditions. An increase in emission line intensity from N II was observed by increasing the pressure and RF power. We used Ti II lines to estimate the plasma temperature by using the Boltzmann equation, and we obtained the density from the Ti II line (454.9 nm) through Stark broadening. In addition, a Mach-Zehnder interferometer was employed to make a two-dimensional map of the electron density at early times. The estimated temperatures and densities are between 0.8 and 2.0 eV and 1017 – 1018 cm−3, respectively. The results suggest that increasing RF power enhanced the Ti-N atoms interaction, which is crucial in titanium nitride film applications.

Study of titanium nitride film growth by plasma enhanced pulsed laser deposition at different experimental conditions

In this work, we have combined a conventional pulsed laser deposition (PLD) system with a dual radio frequency (RF) discharge to create a plasma-enhanced PLD system, known as (PE-PLD). This system was used to grow titanium nitride (TiN) thin films in order to study the feasibility of obtaining control over the nitrogen concentration and the deposition rate. The characterization of the RF plasma was performed using an RF compensated Langmuir probe, while atomic force microscopy (AFM), optical profilometry, Raman spectroscopy, and x-ray diffraction (XRD) were used to analyze the deposited thin films. We observed a significantly enhanced nitrogen concentration and deposition rate as a function of the RF plasma parameters, substrate temperature, and deposition time. Furthermore, we have observed that, using a dual RF configuration, it becomes possible to modify independently the flow and the bombardment energy of the nitrogen ions that impact the substrate. These means allow the control of the nitrogen concentration and deposition rate.

Plasma-enhanced pulsed laser deposition of copper oxide and zinc oxide thin films

Plasma-Enhanced Pulsed Laser Deposition (PE-PLD) is a technique for depositing metal oxide thin films that combines traditional PLD of metals with a low-temperature oxygen background plasma. This proof-of-concept study shows that PE-PLD can deposit copper oxide and zinc oxide films of similar properties to ones deposited using traditional PLD, without the need for substrate heating. Varying the pressure of the background plasma changed the stoichiometry and structure of the films. Stoichiometric copper oxide and zinc oxide films were deposited at pressures of 13 Pa and 7.5 Pa, respectively. The deposition rate was ∼5 nm/min and the films were polycrystalline with a crystal size in the range of 3 nm–15 nm. The dominant phase for ZnO was (110) and for CuO, they were (020) and (111¯), where (020) is known as a high-density phase not commonly seen in PLD films. The resistivity of the CuO film was 0.76 ± 0.05 Ω cm, in line with films produced using traditional PLD. Since PE-PLD does not use substrate heating or post-annealing, and the temperature of the oxygen background plasma is low, the deposition of films on heat-sensitive materials such as plastics is possible. Stoichiometric amorphous zinc oxide and copper oxide films were deposited on polyethylene (PE) and polytetrafluoroethylene (PFTE).

Analysis of plasma enhanced pulsed laser deposition of transition metal oxide thin films using medium energy ion scattering

In this study, plasma-enhanced pulsed laser deposition (PE-PLD), which is a novel variant of pulsed laser deposition that combines laser ablation of metal targets with an electrically-produced oxygen plasma background, has been used for the fabrication of ZnO and Cu2O thin films. Samples prepared using the PE-PLD process, with the aim of generating desirable properties for a range of electrical and optical applications, have been analysed using medium energy ion scattering. Using a 100 keV He+ ion beam, high resolution depth profiling of the films was performed with an analysis of the stoichiometry and interface abruptness of these novel materials. It was found that the PE-PLD process can create stoichiometric thin films, the uniformity of which can be controlled by varying the power of the inductively coupled plasma. This technique showed a high deposition rate of ∼0.1 nm s−1.

Radio-frequency oxygen-plasma-enhanced pulsed laser deposition of IGZO films

We demonstrate the crystalline structures, optical transmittance, surface and cross-sectional morphologies, chemical compositions, and electrical properties of indium gallium zinc oxide (IGZO)-based thin films deposited on glass and silicon substrates through pulsed laser deposition (PLD) incorporated with radio-frequency (r.f.)-generated oxygen plasma. The plasma-enhanced pulsed laser deposition (PEPLD)-based IGZO thin films exhibited a c-axis-aligned crystalline (CAAC) structure, which was attributed to the increase in Zn-O under high oxygen vapor pressure (150 mTorr). High oxygen vapor pressure (150 mTorr) and low r.f. power (10 W) are the optimal deposition conditions for fabricating IGZO thin films with improved electrical properties.

Modelling of laser ablation and reactive oxygen plasmas for pulsed laser deposition of zinc oxide

Pulsed laser deposition (PLD) in a low-pressure oxygen atmosphere is commonly used for the production of high-quality, stoichiometric zinc oxide thin films. An alternative approach that has the potential benefit of increased process control is plasma-enhanced PLD, i.e. the use of a low-temperature oxygen plasma instead of a neutral gas. So far, the development of PE-PLD, and PLD in general, has been hampered by a lack of detailed understanding of the underpinning physics and chemistry. In this paper, we present modelling investigations aimed at further developing such understanding. Two-dimensional modelling of an inductively-coupled radio-frequency oxygen plasma showed that densities of 1014–1015cm−3 of reactive oxygen species O and O2* can be produced for operating pressures between 3 and 100Pa. Together with the absolute densities of species, also the ratio between different reactive species, e.g. O and O2*, can be controlled by changing the operating pressure. Both can be used to find the optimum conditions for stoichiometric zinc oxide thin film deposition. Additionally, we investigated laser ablation of zinc using a different two-dimensional hydrodynamic code (POLLUX). This showed that the amount of material that is ablated increases from 2.9 to 4.7μg per pulse for laser fluences from 2 to 10J/cm2. However, the increased laser fluence also results in an increased average ionisation of the plasma plume, from 3.4 to 5.6 over the same fluence range, which is likely to influence the chemistry near the deposition substrate and consequently the film quality.

Enhanced Performance of GaN-Based Green Light-Emitting Diodes with Gallium-Doped ZnO Transparent Conducting Oxide

Ga-doped ZnO (GZO) transparent conducting oxide was grown by oxygen plasma-enhanced pulsed laser deposition. GZO grown in the presence of oxygen radicals had resistivity of 1 × 10−3 Ω cm and average visible (500–700 nm) transmittance of 92.5%. A low specific contact resistance of 6.5 × 10−4 Ω cm2 of GZO on p-GaN was achieved by excimer laser annealing (ELA) treatment of p-GaN before GZO electrode deposition. The ELA-treated light emitting diode (LED) fabricated with the GZO electrode as a current-spreading layer resulted in light-output power enhanced by 56.2% at 100 mA compared with that fabricated with a conventional Ni/Au metal electrode. The high-light output and low degradation of light-output power were attributed to the decrease in contact resistance between the p-GaN layer and the GZO electrode and uniform current spreading over the p-GaN layer. In addition, low contact resistance results in a decrease of self-heat generation during current drive.

Room temperature radio-frequency plasma-enhanced pulsed laser deposition of ZnO thin films

In this study, we compared the crystalline structures, optical properties, and surface morphologies of ZnO thin films deposited on silicon and glass substrates by conventional pulsed laser deposition (PLD) and radio-frequency (RF) plasma-enhanced PLD (RF-PEPLD). The depositions were performed at room temperature under 30–100mTorr pressure conditions. The RF-PEPLD process was found to have deposited a ZnO structure with preferred (002) c-axis orientation at a higher deposition rate; however, the RF-PEPLD process generated more defects in the thin films. The application of oxygen pressure to the RF-PEPLD process reduced defects effectively and also increased the deposition rate.

Mechanism for Low Temperature Growth of Boron Nitride Nanotubes

Selective growth of boron nitride nanotubes (BNNTs) was demonstrated by plasma-enhanced pulsed laser deposition (PE-PLD). Although PLD is a physical vapor deposition technique for the growth of bor...

Deposition of orthorhombic boron nitride films by plasma-enhanced pulsed laser deposition

In this paper, high quality orthorhombic boron nitride （o-BN） films were prepared on Si（100） substrate by plasma-enhanced pulsed laser deposition （PE-PLD） for the first time. The films were characterized by Fourier transform infrared （FTIR） spectroscopy，glancing-angle X-ray diffraction （XRD） and atomic force microscopic （AFM）. In the FTIR spectrum of the film, we can see three characteristic peaks around 1189cm-1, 1585cm-1 and 1450cm-1 of o-BN. The diffraction peaks ［111］, ［020］, ［021］, ［310］ and ［243］ all appeared in XRD, especially ［243］ and ［310］ crystal plane diffraction were very strong. The surface morphology was closely observed by AFM photograph.

Improvement of Characteristics of Ga-Doped ZnO Grown by Pulsed Laser Deposition Using Plasma-Enhanced Oxygen Radicals

The authors report on the growth and characterization of Ga-doped ZnO films grown at a low temperature by oxygen plasma-enhanced pulsed laser deposition (PE-PLD). The introduction of oxygen radicals during PLD growth remarkably improved the crystalline quality, surface morphology, and density of Ga-doped ZnO films. The PE-PLD grown Ga-doped ZnO film showed a maximum electron mobility of and a minimum resistivity of at a radio-frequency input power of 100 W. Average visible (500–700 nm) transparency was improved from 83.7% in the Ga-doped ZnO grown without oxygen radicals to 93.1% in the samples grown with oxygen radicals. The use of oxygen radicals also increased the near-IR (800–3000 nm) transparency. The figure of merit of the Ga-doped ZnO film grown at a radio frequency input power of 100 W showed a maximum value of at wavelengths of 580 nm in the visible range and 1100 nm in the near-IR range.

Growth of AlN and TiN Structures by Plasma-Enhanced Pulsed Laser Deposition

AbstractNitride materials are of interest for a wide variety of applications, including wear-resistant coatings, insulating layers, high-temperature semiconductor devices, and short-wavelength emitters and detectors. TiN and AlN appear to be particularly amenable to crystalline thin film deposition, with stoichiometric material easily obtained even without the use of active nitrogen species. This paper describes the growth of crystalline AlN and TiN thin films on silicon and sapphire substrates using a KrF excimer laser (λ = 248 nm) to ablate elemental metallic targets, and an inductively-coupled RF plasma source to supply active nitrogen species. Growth was monitored in-situ using reflection high-energy electron diffraction (RHEED), and films were characterised using fourier-transform infrared spectroscopy (FTIR) and electron microscopy techniques. Optimised growth conditions led to single-crystal growth of TiN on both substrates, but only polycrystalline AlN was formed directly. Use of a TiN buffer layer on (0001) sapphire led to the successful growth of a single-crystal AlN layer as confirmed by RHEED and high-resolution transmission electron microscopy (HRTEM).

Spectroscopic study of the microwave plasma enhanced pulsed laser deposition for Y1Ba2Cu3O7−x superconducting thin films

Microwave plasma enhanced pulsed laser deposition (PE-PLD) technique has successfully in-situ synthesized the epitaxial-like high quality Y1Ba2Cu3O7−x superconducting thin films. It has remarkably improved the films' surface morphology with fine grain, high dense and mirror-smooth. The PE-PLD emission spectra showed abundant active atomic oxygen produced and greatly enhanced in emission intensities of YBCO species sustaining to the substrate surface of extended deposition distance (85 mm), that is believed to explain the improvement of deposition kinetics and surface morphology of YBCO superconducting thin films. The effects of microwave power, laser energy and oxygen pressure on the enhancement were investigated.

Mirror-smooth YBa2Cu3O7−x superconducting films deposited by plasma-enhanced pulsed laser deposition technique

Effect of microwave induced O2- and Ar-plasma on characteristics of YBa2Cu3O7−x (YBCO) superconducting films deposited by pulsed laser deposition technique (PLD) was examined. Surface roughness of the films was greatly improved at the presence of O2-plasma, but was substantially degraded at the presence of Ar-plasma. Epitaxial-like YBCO superconducting films withc-axis perpendicular to the films' surface and witha-andb-axes aligned in films' plane were obtained on (100) MgO substrates. They have onset of transition temperature atTc = 90K and zero atTc0 = 86K. The mechanism for the improvement in this process was investigated by optical emission microscopy (OEM). The production of abundant atomic oxygen in microwave induced oxygen plasma that enhances the surface reaction kinetics is believed to be the main factor for improving surface smoothness of the films.

Modification on the surface of superconducting YBa2Cu3O7−x films by microwave plasma-enhanced pulsed laser deposition

Superconducting YBa2Cu3O7−x films having smooth surfaces were successfully synthesized by a microwave plasma-enhanced pulsed laser deposition (PEPLD) process. Particulates that frequently occurred in films grown by the conventional PLD process were effectively eliminated. The films were epitaxial-like. The c-axis was perpendicular to the films’ surface, the a and b axes were aligned in the films’ plane, and the onset and zero of the transition temperature were at Tc=90 K and Tc0=86 K, respectively. Optical emission spectroscopy indicated that the presence of oxygen plasma not only reexcited the laser-induced species via the collision process, but also produced abundant atomic oxygen in PEPLD process. The surface reaction kinetics for the formation of the thin-film process was thus greatly enhanced, which substantially improved the thin-film quality.