Search

Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga2O3-In2O3 solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga2O3-In2O3 solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca2+ or Zr4+ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca2+ and was 10−13 Ω−1 cm−1, while in the samples doped with Zr4+, the electrical conductivity was the highest and reached 10−3 Ω−1 cm−1. The broadband luminescence of β-Ga2O3-In2O3 solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca2+ or Zr4+ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Gai, VGa, VGaVo) or doping impurities (Zr4+, Ca2+). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the VGa or VGaVO acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca2+ impurities are manifested in the intense excitation band at 4.1 eV. [ABSTRACT FROM AUTHOR]

The effect of the sintering atmosphere on the structural, electrical, and luminescence properties of gallium oxide ceramics was studied using X-ray diffraction, scanning electron microscopy, luminescent spectroscopy, and electrical conductivity methods. A single β-Ga2O3 structure was confirmed by X-ray diffraction. The sintering of ceramics in the argon atmosphere caused structural changes on the surface and an insignificant increase in intrinsic volume. These features were also confirmed by scanning electron microscopy, where a larger number of vacancy-type defects were observed for argon-sintered ceramics rather than in the case of sintering in an oxygen atmosphere. The β-Ga2O3 ceramics exhibited three photoluminescence excitation peaks located at 3.33, 4.52, and 5.3 eV. The emission spectra revealed a broad peak in the 2.0–4.0 eV region, with a maximum at around 3.03 eV. The sintering atmosphere also affected the relative intensity of elementary luminescence bands. The photoluminescence properties are mainly attributed to the radiative recombination of charge carriers through donor–acceptor pairs. It was established that the electrical conductivity of ceramics also strongly depended on the sintering atmosphere. [ABSTRACT FROM AUTHOR]

A series of β-Ga2O3 nanocrystals doped with europium were obtained using a high-energy ball-milling method under different milling conditions. Studied samples were subjected to various analyses, including scanning electron microscopy SEM–EDS, X-ray diffraction, Raman spectroscopy as well as optical (photoluminescence and diffuse reflection) spectroscopies to investigate their morphology, structure, and optical properties. It was shown that the milling chamber material and rotation speed had a significant impact on the properties of the β-Ga2O3 composites, resulting in different crystalline sizes, ranging from 30 nm to 5 μm. Moreover, larger particle sizes exhibited higher host emission, while an inverse correlation was observed for Eu3+ red emission of β-Ga2O3:Eu powder. Additionally, a higher luminescence intensity was observed for the nanocomposite samples obtained under the milling in ZrO2 chamber. [ABSTRACT FROM AUTHOR]

β-Ga2O3 nanocrystals have been successfully obtained by the high-energy ball milling method. The obtained nanocrystalline powders have been characterized using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and luminescent spectroscopy. X-ray diffraction patterns show a single gallium oxide structure formed in the milling process with a small amount of α-Ga2O3 phase. The grains of irregular shape were identified with the TEM technique. HRTEM images confirmed the formation of the β-Ga2O3 nanocrystals with a size distribution of 50–80 nm. Three luminescence bands peaked at about 2.52, 2.91, and 3.26 eV were observed in photoluminescence spectra. The gradual blue shift of the emission maxima at the excitation in the fundamental absorption edge under the different milling conditions was detected. [ABSTRACT FROM AUTHOR]

Microdefects in β-Ga2O3 and β-Ga2O3:0.1 % Mg single crystals grown by the method of floating zone technique with radiation heating have been studied. Porous defects with a tube-like shape were found on the (100) surface and in the bulk of undoped β-Ga2O3 crystals. Such defects are up to 1 μm in diameter and up to 100 μm in length, elongated along the [010] axis. Doping of gallium oxide with magnesium ions leads to a decrease in the concentration of defects and changes in their shape. The concentration and mobility of electrical charge carriers in undoped β-Ga2O3 crystals were calculated. The activation energies of the conductivity of the studied crystals were estimated. Some correlations between crystal growing conditions, doping, and the rate of Ga2O evaporation from the melt and defect density were revealed and discussed, providing aspects for further material development. The mechanisms of these defects formation have been also analyzed. [ABSTRACT FROM AUTHOR]

The temperature-dependencies of the X-ray excited luminescence spectra were measured from unintentionally doped, annealed in oxygen and Mg-doped β-Ga2O3 crystals prepared by the floating zone growth method. The crystals exhibited ultraviolet, blue and green luminescence bands. It was established that the luminescence intensity is strongly dependent on resistivity of the crystal. For the as-grown sample with a high electron concentration, the main luminescence band at 300 K was blue. The blue luminescence band was observed over a wide range of temperatures, and the thermal quenching of luminescence was observed only at T > 400 K. The blue luminescence band was suppressed in high-resistance crystals, in particular in oxygen annealed and heavily doped β-Ga2O3 crystals with 1% Mg, while the UV band, on the contrary, increased and prevailed at low temperatures. Activation energies of separate luminescence bands and conductivity in the investigated crystals are calculated. Some correlations between conductivity and luminescence parameters were found and discussed to give hints for the further development of this material. [ABSTRACT FROM AUTHOR]

Detailed investigations of the spectroscopic properties of Cr3+ ions in β-Ga2O3:0.05% Cr3+ single crystals grown by the floating zone technique have been performed in the temperature range 4.5–550 K. The luminescence of Cr3+ ions at low temperatures is due to narrow R-lines (2E → 4A2 transitions) and their vibronic sidebands, whereas the broad intense band (4T2 → 4A2 transition) dominates at temperatures above 200 K. The vibronic sidebands of R-lines with amplitude of less than 5% of the R1-line at a temperature of 4.5 K cover the region of 700–735 nm. The temperature dependences of the luminescence intensity and the decay time of Cr3+ ions indicate the same mechanism of quenching of R-line intensity and shortening of lifetime for 2E of Cr3+ ions. The temperature dependence of the R1-line decay time of β-Ga2O3:Cr3+ with maximal temperature coefficient |Δτ/ΔT| = 0.023 ms K−1 at 120 K and maximal specific sensivitity |(Δτ/ΔT)τ−1| = 0.017 K−1 at 160 K indicates an application potential of this phosphor for low-temperature fluorescence thermometry. [ABSTRACT FROM AUTHOR]

Changes in the defect structure and luminescence properties of silicon p-type crystals surface layer under the influence of plastic deformation and high temperature annealing in oxygen atmosphere were investigated. A special role of dislocations in the surface layer of silicon during the formation its energy spectrum and rebuilding the defective structure was established. It is shown that the concentration of linear defects more than 104 cm−2 enriched subsurface layer with electrically-active complexes (dislocation—oxygen, dislocation—vacancy, dislocation—interstitial atoms of silicon) that are effective radiative recombination centers. It has been demonstrated that mixed treatment of silicon crystals by plastic deformation, high temperature annealing in the flowing oxygen atmosphere and elastic deformation at the final stage increases the energy efficiency of the radiative structures. [ABSTRACT FROM AUTHOR]

Detailed investigations of the spectroscopic properties of Cr3+ ions in β-Ga2O3:0.05% Cr3+ single crystals grown by the floating zone technique have been performed in the temperature range 4.5–550 K. The luminescence of Cr3+ ions at low temperatures is due to narrow R-lines (2E → 4A2 transitions) and their vibronic sidebands, whereas the broad intense band (4T2 → 4A2 transition) dominates at temperatures above 200 K. The vibronic sidebands of R-lines with amplitude of less than 5% of the R1-line at a temperature of 4.5 K cover the region of 700–735 nm. The temperature dependences of the luminescence intensity and the decay time of Cr3+ ions indicate the same mechanism of quenching of R-line intensity and shortening of lifetime for 2E of Cr3+ ions. The temperature dependence of the R1-line decay time of β-Ga2O3:Cr3+ with maximal temperature coefficient |Δτ/ΔT| = 0.023 ms K−1 at 120 K and maximal specific sensivitity |(Δτ/ΔT)τ−1| = 0.017 K−1 at 160 K indicates an application potential of this phosphor for low-temperature fluorescence thermometry. [ABSTRACT FROM AUTHOR]

Undoped and Mg 2+ -doped β-Ga 2 O 3 -20% In 2 O 3 solid solution microcrystalline samples were synthesized using the high-temperature solid-state chemical reaction method to investigate the influence of native defects on structural, luminescent, and electrical properties. The synthesis process involved varying the oxygen partial pressure by synthesizing samples in either an oxygen or argon atmosphere. X-ray diffraction (XRD) analysis confirmed the monoclinic structure of the samples with the lattice parameters and unit cell volume fitting well to the general trends of the (Ga 1-x In x ) 2 O 3 solid solution series. Broad emission spectra ranging from 1.5 to 3.5 eV were registered for all samples. Luminescence spectra showed violet, blue, and green emission elementary bands. The luminescence intensity was found to vary depending on the synthesis atmosphere. An argon synthesis atmosphere leads to increasing violet luminescence and decreasing green luminescence. Intense bands at about 4.5 and 5.0 eV and a low-intensity band at 3.3 eV are presented in the excitation spectra. The electrical conductivity of the samples was also determined depending on the synthesis atmosphere. The high-resistance samples obtained in an oxygen atmosphere exhibited activation energy of around 0.98 eV. Samples synthesized in an argon atmosphere demonstrated several orders of magnitude higher conductivity with an activation energy of 0.15 eV. The results suggest that the synthesis atmosphere is crucial in determining the luminescent and electrical properties of undoped β-Ga 2 O 3 -In 2 O 3 solid solution samples, offering the potential for various optoelectronic applications., Competing Interests: The authors declare no conflict of interest.

The effect of a weak magnetic field (B = 0.17 T) and X-irradiation (D < 520 Gy) on the rearrangement of the defective structure of near-surface p-type silicon layers was studied. It was established that the effect of these external fields increases the positive accumulated charge in the region of spatial charge (RSC) and in the SiO2 dielectric layer. This can be caused by both defects in the near-surface layer of the semiconductor and impurities contained in the dielectric layer, which can generate charge carriers. It was found that the near-surface layers of the barrier structures contain only one deep level in the silicon band gap, with an activation energy of Ev + 0.38 eV. This energy level corresponds to a complex of silicon interstitial atoms SiI+SiI. When X-irradiated with a dose of 520 Gy, a new level with the energy of Ev + 0.45 eV was observed. This level corresponds to a point boron radiation defect in the interstitial site (BI). These two types of defect are effective in obtaining charge carriers, and cause deterioration of the rectifier properties of the silicon barrier structures. It was established that the silicon surface is quite active, and adsorbs organic atoms and molecules from the atmosphere, forming bonds. It was shown that the effect of a magnetic field causes the decay of adsorbed complexes at the Si−SiO2 interface. The released hydrogen is captured by acceptor levels and, as a result, the concentration of more complex Si−H3 complexes increases that of O3−Si−H.

Changes of the defect structure of silicon p-type crystal surface layer under the influence of plastic deformation and high temperature annealing in oxygen atmosphere were investigated by deep-level capacitance-modulation spectroscopy (DLCMS) and IR spectroscopy of molecules and atom vibrational levels. Special role of dislocations in the surface layer of silicon during the formation of its energy spectrum and rebuilding the defective structure was established. It is shown that the concentration of linear defects (N ≥ 10 4  cm -2 ) enriches surface layer with electrically active complexes (dislocation-oxygen, dislocation-vacancy, and dislocation-interstitial atoms of silicon) which are an effective radiative recombination centers.