L. S. Parshina

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.

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.

Influence of the conditions of pulsed laser deposition on the structural, electrical, and optical properties of VO2 thin films

The technique of pulse laser deposition with the separation of plume drops is used to produce VO2 thin films on sapphire(0001) and silicon(111) substrates. It is established that the energy density at the target and the oxygen pressure influence the structural and electrical properties of the films. All of the VO2 crystal films exhibit semiconductor-metal transitions with a substantial change in the resistance (by 2–5 orders of magnitude). The transmittance in the range 200–800 nm and reflectance in the range 400–700 nm are studied in the temperature range from 20 to 100°C. The transmittance of the films at wavelengths from 300 to 800 nm shows a jump and hysteresis upon heating and cooling. It is for the first time established that the changes in the transmittance of the film are different in character at different wavelengths and the shape of the temperature hysteresis loop for optical transmittance in the visible and near-ultraviolet regions does not in all areas replicate the shape of the hysteresis loop for the resistivity of the VO2 films. The difference in the behavior of the hysteresis curves for the transmittance and resistance is attributed to variations in the absorption of the films under variations in temperature.

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.

Influence of Oxygen Vacancies on the Magnetic Properties of Zn 1 – x Co x O y Films

Thin films of Zn1 – xCoxOy (х = 0–0.3) with a temperature of the ferromagnetic transition of ТС > 300 K are obtained from ZnO–Co3O4 ceramic targets. The electron concentration in the films is found to decrease exponentially with increasing cobalt content. It is revealed that the magnetization of the films obtained under oxygen deficiency conditions varies in a nonmonotonous way as the cobalt concentration increases. This is caused by the oxidation of metallic nanoclusters of cobalt due to an increase in the oxygen content in the targets. Investigation of the transmission spectra of Zn1 – xCoxOy films revealed extrema in the visible region of the spectrum and near the edge of the fundamental absorption band, associated with electron states introduced by cobalt.

Vanadium- and Titanium Dioxide-Based Memristors Fabricated via Pulsed Laser Deposition

Thin TiOx and VO2 – x films are fabricated via pulsed laser deposition from metal targets with the help of mask technologies. Their memristive properties are investigated using Au/TiOx1/TiOx2/Au and Au/VO2/VO2 – x/Au thin-film structures, and the possible mechanisms of resistive switching are discussed. The structures are obtained at room temperature in an oxygen atmosphere.

Pulse laser deposition of vanadium dioxide films

Thin amorphous and crystalline films of VO2 are obtained on (0001) sapphire substrates via pulsed laser deposition with the speed separation of particles under a variety of deposition conditions. The electrical and optical properties of the films in the vicinity of the phase transition in the temperature range of 20 to 100°C are studied. The temperature of transition (Tc) and the width of the hysteresis are found to be 67.5 and 3°C, respectively.