A. A. Lotin

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).

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.

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.

Effect of energy density on the target on SnO2:Sb film properties when using a high-speed particle separator

SnO2:Sb thin films are grown by pulsed laser deposition with high-speed particle separation on quartz-glass substrates without post-deposition annealing under different deposition conditions in the range of the energy densities on the target from 3.4 to 6.8 J/cm2. Their optical, structural, and electrical properties are studied. It is found that the energy density on the target affects the SnO2:Sb film conductivity and transmittance. The optimum conditions of film growth by the droplet-free pulsed laser deposition method are determined. A resistivity minimum of 1.2 × 10–3 Ω cm is observed at an energy density on the target of 4.6 J/cm2, a substrate temperature of 300°C, and an oxygen pressure of 20 mTorr in the vacuum chamber during deposition.

Time-of-Flight Characteristics of a Laser Torch during Ablation of a MnSi Target in Argon Atmosphere

The Langmuir-probe technique has been used to study the time-of-flight characteristics of a laser torch during MnSi-target ablation in vacuum and argon atmosphere by pulsed 532-nm laser radiation at 15-ns pulse duration. It is established that the amplitude of the signal of fast particles in the laser torch nonmonotonically depends on the buffer-gas pressure. Mechanisms determining this dependence of laser-torch characteristics on the pressure are considered. The influence of buffer-gas pressure on the ion-velocity distribution function is determined.

Photoluminescence properties of thin nitrogen- and phosphorus-doped ZnO films fabricated using pulsed laser deposition

The production of n- and p-type high-quality film structures is a foreground task in tackling the problem of growing the light-emitting p-n junctions based on zinc oxide. The ZnO:N and ZnO:P thin-film samples are produced from ceramic targets using the pulsed laser deposition. Zn3N2, MgO, and Zn3P2 are introduced in the ZnO ceramic targets for the fabrication of the p-type ZnO films. Gases O2 and N2O are used as buffer gases. The thermal annealing of the ZnO films is employed. The resistance and photoluminescence (PL) spectra of the ZnO films are measured prior to and after annealing. The dependence of the ZnO PL peak amplitude and position prior to and after annealing on the level of doping with nitrogen and phosphorus is established. The PL characteristics of the films are studied at cw optical excitation using a He-Cd laser with a radiation wavelength of 325 nm. The PL spectra in the interval 300–700 nm are recorded by an HR4000 Ocean Optics spectrometer in the temperature range 10–400 K. The effect of the conditions for the film deposition on the PL spectra is analyzed. The effect of the N- and P-doping level of the ZnO films on the PL intensity of the films and the position of the PL bands in the UV region is investigated. The short-wavelength (250–400 nm) transmission spectra of the ZnO:P films are measured. The effect of the P-doping level on the band gap of the ZnO films is studied.

Quantum efficiency increasing and lasing in the quantum wells based on ZnO

The Mg0.27Zn0.73O/ZnO multiple quantum wells with different well width Lw have been grown by pulsed laser deposition method. The interface roughness of quantum wells was inherited from the bottom one and did not exceed 1 nm. The quantum confinement effect has been observed. The exciton binding energy of the two-dimensional Mg0.27Zn0.73O/ZnO structures was two times higher in comparison with the bulk ZnO. A sharp increase of exciton peak intensity in the photoluminescence spectra at well width reduction was observed. The optical excited stimulated emission in quantum wells Mg 0.27Zn0.73O/ZnO with an excitation threshold ~210 kW/cm2 has been demonstrated.

Luminescence Properties of Cd x Zn 1 – x O Thin Films

Thin CdxZn1 – xO films with a Cd content in the range from zero to 35 at % are synthesized by pulsed laser deposition. A record-breaking solubility limit of 30 at % of Cd in wurtzite-structured CdxZn1 – xO thin films is attained. Apart from the exciton peak, additional peaks associated with an inhomogeneous distribution of Cd in the samples are observed in the low-temperature (10 K) photoluminescence spectra of Cd0.15Zn0.85O and Cd0.3Zn0.7O films. An unsteady (S-like) temperature dependence of the spectral position of the exciton photoluminescence peak in CdxZn1 – xO films is observed. Such a dependence is associated with the effect of the localization of charge carriers.