O. A. Novodvorsky

Optical and structural characteristics of Ga-doped ZnO films

The n-ZnO films doped with Ga to the content 2.5 at % are produced by pulse laser deposition onto the (0001) oriented single crystal sapphire substrates. The transmittance spectra of the ZnO films in the range from 200 to 3200 nm are studied in relation to the Ga dopant content. It is established that an increase in the Ga content shifts the fundamental absorption edge to the blue region, but reduces the transparency of the ZnO films in the infrared spectral region. The dependence of the band gap on the level of doping with Ga is determined. The photoluminescence spectra of the ZnO films doped to different levels are recorded. It is established that the PL intensity and peak position vary unsteadily with the level of doping. X-ray diffraction studies of the structure of the films are carried out. It is found that the crystallographic parameters (the lattice constant c) of the ZnO film depend on the Ga dopant content and the conditions of deposition of the films.

Pulsed laser deposition of ITO thin films and their characteristics

The indium tin oxide (ITO) thin films are grown on quartz glass substrates by the pulsed laser deposition method. The structural, electrical, and optical properties of ITO films are studied as a function of the substrate temperature, the oxygen pressure in the vacuum chamber, and the Sn concentration in the target. The transmittance of grown ITO films in the visible spectral region exceeds 85%. The minimum value of resistivity 1.79 × 10−4 Ω cm has been achieved in the ITO films with content of Sn 5 at %.

Growth of magnetic eutectic GaSb-MnSb films by pulsed laser deposition

Eutectic GaSb + MnSb films ranging in thickness from 80 to 130 nm have been grown on sapphire substrates by pulsed laser deposition using mechanical droplet separation. The films were similar in composition to the ablation target, consisting of the eutectic GaSb-MnSb alloy. According to atomic force and electron microscopy data, the films were homogeneous, with p-type conductivity. Their electrical properties depended significantly on deposition conditions. The best films had a resistivity of 7 × 10−3 Ω cm, carrier concentration of 8.1 × 1019 cm−3, and carrier mobility of 102 cm2/(V s). Characteristically, the films had a negative magnetoresistance. Their magnetization curves showed saturation in a magnetic field of ∼1 × 10−1 T. According to the magnetic-field dependences, the coercive force in the films was within 3 × 10−2 T; that is, the films were soft magnets with a small domain size.

Characterization of ZnO:Ga and ZnO:N films prepared by PLD

The thin films of zinc oxide have been produced by the pulse laser deposition method at various levels of gallium and nitrogen doping. To obtain the n-type films we used gallium doping with concentration of gallium from zero up to 5 at %. The dependence of photoluminescence of the epitaxial ZnO:Ga films on the concentration of gallium doping has been studied. An optimum range of the n-type ZnO films doping with gallium has been determined to obtain highly effective films from the viewpoint of realizing p-n transitions. This range, on the one hand, defines the maximal PL amplitude and, on the other hand, specifies the minimal specific resistance that corresponds to an interval of 0.125–1.000 at % Ga. To produce the p-type ZnO:(Ga, N) films, the ZnO targets with the content of GaN from zero up to 2 at % were used. N2O was used as a buffer gas. A difference is observed in the positions of the peaks of the emission lines of the photoluminescence spectra for the ZnO films, doped with gallium (Ga) and co-doped with gallium and nitrogen (N).

Characterization of the erosion plume after ablation of copper and tantalum targets by excimer laser irradiation

The erosion plume resulting from ablation of copper and tantalum targets in vacuum with excimer laser irradiation (308 nm) was studied using Langmuir probe and optical emission spectroscopy. The ion and electron probe currents were obtained in the range of energy densities from 0.2 to 2.2 J/cm2 at the target with a probe-to-target distance from 10 to 133 mm. The ion velocity distribution calculated from the time-of-flight measurements has been revealed as a multimodal kind. Curves of the spatial and time dependence of electron probe current were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between the Langmuir probe and target. It was established that the plume electron temperature is nonuniform and it has a maximum in front of the plume. The optical emission spectra were used to study the plume composition qualitatively. In addition, the optical emission spectroscopy allowed us to measure both t...

Ternary alloys Cd y Zn 1 − y O and Mg x Zn 1 − x O as materials for optoelectronics

Thin films of CdyZn1 − yO and MgxZn1 − xO (y = 0−0.35, x = 0−0.45) ternary alloys have been grown by pulsed laser deposition onto sapphire substrates. The record solubility limits of Cd (y = 0.3) and Mg (x = 0.35) have been achieved in hexagonal zinc oxide. The mismatch of the lattice parameters a of Cd0.2Zn0.8O and Mg0.35Zn0.65O does not exceed 1%; in this case, the band gap discontinuity is 1.3 eV. The surface roughness of the films does not exceed 2.5 nm at x = 0−0.27 and y = 0−0.20.

Epitaxial growth and properties of MgxZn1-xO films produced by pulsed laser deposition

The MgxZn1-xO thin films with a Mg content corresponding to x = 0–0.45 are grown by pulsed laser deposition on ablation of ceramic targets. The conditions for epitaxial growth of the films on the single-crystal Al2O3 (00.1) substrates are established. The record limit of solubility of Mg in hexagonal ZnO, x = 35 is attained. In this case, the lattice mismatch for the parameter a of the ZnO and Mg0.35Zn0.65O films does not exceed 1%, whereas the band gaps of the films differ by 0.78 eV. The surface roughness of the films corresponds to 0.8–1.5 nm in the range of x = 0–0.27.

Energy distribution of ions in plasma formed by laser ablation of metallic Nb and Ta targets

Abstract The laser plasma plume expansion induced by UV nanosecond irradiation from metallic Nb and Ta targets has been studied using Langmuir probe time-of-flight measurements. The ion current shape was measured as a function of the laser radiation flux at various probe-to-target distances. The ion velocity distribution and the ion energy spectra have been determined by measuring the time of flight of ions reaching the Langmuir probe. A multi-mode velocity distribution of ions has been revealed. The dependence of the amplitudes of the plume energy components on the plume scatter time and on the laser radiation flux has been investigated. The experimental time-of-flight data have been compared with a Maxwell velocity distribution. The threshold values of the laser intensity were determined for different distribution modes in the ion energy spectrum.

Ion energy spectrum control in modified cross-beam pulsed laser deposition method

The time-of-flight curves of the ion current to a probe in a plasma beam formed by crossing plumes from two laser-ablated silicon targets have been measured using the Langmuir probe technique. It is established for the first time that the ion energy spectrum of the plasma beam formed by the two laser erosion plumes and oriented in the direction of the bisector of the angle between the initial plumes can be modified by changing the angle between them (i.e., between the erosion plume). A modified cross-beam pulsed laser deposition method is proposed, which allows the energies of deposited particles to be controlled in a broad range.

Properties of Zn1 − xCoxO films produced by pulsed laser deposition with fast particle separation

The study is concerned with the structural, optical, magnetic, and transport properties of Zn1 − xCoxO (x = 0.05–0.45) films produced on Al2O3 (0001) substrates at a temperature of Ts = 500°C by pulsed laser deposition with fast particle separation. The film thickness is d = 60–300 nm. It is found that the Zn1 − xCoxO ternary alloy retains its wurtzite-type crystal structure up to x = 0.35, if the films are produced at low buffer-oxygen pressures (∼10−6 Torr). It is established that, in these conditions, the electron concentration is higher than 1020 cm−3 because of the high density of oxygen donor vacancies. In this case, the films start to exhibit ferromagnetism in the magnetization and the anomalous Hall effect at temperatures above 100 K. The sign of the anomalous Hall effect is found to be positive and opposite to the sign of the normal Hall effect, as occurs in Co metal layers. This is indicative of the cluster nature of ferromagnetism of the Zn1 − xCoxO films. For thin Zn1 − xCoxO layers (d = 60 nm, x = 0.2) in a transverse magnetic field, profound hysteresis of the magnetoresistance is observed, which is indicative of the out-of-plain easy axis of magnetization of the films. The magnetic anisotropy is attributed to the structuring of the layers (elongation of magnetic clusters along the growth axis of the films). The structuring can lead to noticeable strengthening of the layer ferromagnetism.