Doped Crystals Research Articles

Surface doping of rubrene single crystals by molecular electron donors and acceptors.

The surface molecular doping of organic semiconductors can play an important role in the development of organic electronic or optoelectronic devices. Single-crystal rubrene remains a leading molecular candidate for applications in electronics due to its high hole mobility. In parallel, intensive research into the fabrication of flexible organic electronics requires the careful design of functional interfaces to enable optimal device characteristics. To this end, the present work seeks to understand the effect of surface molecular doping on the electronic band structure of rubrene single crystals. Our angle-resolved photoemission measurements reveal that the Fermi level moves in the band gap of rubrene depending on the direction of surface electron-transfer reactions with the molecular dopants, yet the valence band dispersion remains essentially unperturbed. This indicates that surface electron-transfer doping of a molecular single crystal can effectively modify the near-surface charge density, while retaining good charge-carrier mobility.

Raman spectroscopy of silicon, doped with platinum and irradiated by protons

In this work, the influence of proton irradiation and platinum impurities on the crystal structure of silicon samples was studied by Raman spectroscopy. It has been established that the doping of single crystals of Si with platinum leads to minor changes and the appearance of new vibrations in the Raman spectra. The intensity of the main silicon peak at 521 cm–1 decreases by a factor of 1.6, while its FWHM practically does not change and is about 4.0 cm–1. Such a decrease in the intensity of the peak is probably due to the weakening and breaking of bonds in the structure of the silicon crystal lattice due to the diffusion of Pt. It is shown that the appearance of new vibrations in the range 60–280 cm–1 in the spectra of Si<Pt> is associated with the presence of elemental Pt and the formation of PtSi. It has been found that irradiation of Si<Pt> samples with 600 keV protons leads to a change in the Raman spectra, and the peaks from Pt and/or PtSi disappear.

Growth and spectroscopic properties of Tm3+ doped YPO4 crystal

Good quality single crystal of Tm3+ doped YPO4 crystal with an astounding emission cross-section was grown utilizing the flux method and the KF–P2O5 flux was employed for the first time to grow YPO4 crystal.

Conductivity in sulfur doped gallium selenide crystals measured by terahertz time-domain spectroscopy

In this work, the conductivity of intrinsic GaSe, S doped 2.5 mass% GaSe (GaSe: S(2.5%)), and S doped 7 mass% GaSe (GaSe: S(7%)) crystals, in a frequency range of 0.3–2.5 THz, is measured by transmission terahertz time-domain spectroscopy, and fitted with Drude-Smith-Lorentz model which is introduced by lattice vibration effect. It is found that the real part of conductivity decreases with the augment of S doping, which is caused by the gradual shift of the Fermi energy level of GaSe crystals to the charge neutrality level due to the generation of substitution impurities and gap impurities by S doping, resulting in the reduction of carrier concentration. The intrinsic GaSe and GaSe: S(2.5%) have a clear lattice vibration peak at about 0.56 THz, while GaSe: S(7%) has no lattice vibration peak near 0.56 THz, which is mainly due to the S doping increasing the structural hardness of the crystal and reducing the interlayer rigidity vibration of the crystal. All three samples have the obvious narrow lattice vibration peaks at about 1.81 THz, and the intensities that first decrease and then increase with the augment of S doping, which is mainly due to the fact that a small amount of S doping can reduce the local structural defects of GaSe and weaken the intensity of the narrow lattice vibration peak, while excessive S doping can generate the β-type GaS crystal, increase the local structural defects of the crystals and the intensity of the narrow lattice vibration peak. With the increase of S doping, the intensity of the broad lattice vibration peak of GaSe crystal weakens or even disappears at about 1.07 THz and 2.28 THz, mainly due to the S doping resulting in the substitution of S for impurities and GaS gap impurities, which reduces the fundamental frequency phonon vibration intensity, thereby weakening the lattice vibration caused by the second-order phonon difference mode of the crystal. The results show that the appropriate concentration of S doping can effectively suppress the lattice vibration of GaSe crystal and reduce the conductivity and power loss in the THz band. This study provides important data support and theoretical basis for the design and fabrication of low loss THz devices.

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Pyroelectric effect in doped nonpolar glycine crystals

Doping-induced local symmetry breaking of centrosymmetric molecular crystals endows them with piezoelectric and pyroelectric properties. In this work, we measured temperature dependences of pyroelectric and piezoelectric coefficients in α--glycine crystals single-doped by threonine and double-doped by threonine and alanine. We analyzed primary and secondary pyroelectric effects in these crystals and suggested a model of the dopant complexes related to the observed effects. Keywords: pyroelectricity, α-glycine, doped molecular crystals.

ELECTRONIC STATES DENSITY, RESISTIVITY, AND PHASE COMPOSITION OF CaTiO3 PEROVSKITE WITH ISOMORPHIC IMPURITY OF NIOBIUM

The application of materials with a perovskite structure has currently become one of the most promising approaches for the development of photovoltaic systems. A method for high-speed synthesis (under 15 minutes) of CaTiO3 perovskite — TiO2 rutile with the possibility of concurrent doping of the product has been developed. The density of electronic states, phase composition features, and resistivity of niobium-doped perovskite (CaTiO3) were investigated. The calculations of the density of electronic states for niobium-doped CaTiO3 have shown that at low concentrations of niobium, the samples exhibit conductivity characteristic of semiconductors. Since niobium has one more valence electron compared to titanium, as the niobium content increases, the Fermi level shifts to the band of free states. This shift of the Fermi level should lead to a change in the nature of the conductivity of doped crystals, eventually transitioning to metallic conductivity at high concentrations of niobium. Composite analysis (СаТіО3+ТіО2) by X-ray diffraction has shown that the use of niobium as a doping element significantly accelerates the CaTiO3 synthesis reaction, and increases the perovskite concentration in the sample. The concentration of CaTiO3 in the sample the with niobium is 83 % vol. at a temperature of 900ºC and at a synthesis time of 5 min, whereas when using a mixture without Nb, the content of perovskite will be only 58 % vol. at a synthesis time of 12 min. X-ray phase analysis methods confirm the formation of a solid solution (doping) Ca(Ti,Nb)O3, resulting in the preparation of samples (СаТіО3+ТіО2) with resistivity inherent to semiconductors.

Влияние примеси тулия на диэлектрические и пироэлектрические свойства монокристаллов ниобата бария стронция

It has been shown that the introduction of thulium impurity into the crystals of strontium barium (SBN:61) niobate leads to an increase in the dielectric constant value and the blur region of the phase transition. External field polarization partially stabilizes the polar state of the samples, however, the heterogeneous distribution of polarization across the thickness of the studied samples indicates the existence of regions with a developed domain structure characteristic of highly doped crystals.

Influence of thulium impurity on dielectric and pyroelectric properties of single crystals of Barium Strontium Niobate

It has been shown that the introduction of thulium impurity into the crystals of strontium barium (SBN : 61) niobate leads to an increase in the dielectric constant value and the blur region of the phase transition. External field polarization partially stabilizes the polar state of the samples, however, the heterogeneous distribution of polarization across the thickness of the studied samples indicates the existence of regions with a developed domain structure characteristic of highly doped crystals. Keywords: Ferroelectrics, relaxors, pyroelectric effect, polarization distribution, single crystal, SBN.

Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.

Growth of Pentacene-Doped p-Terphenyl Crystals Using SSVBT and Doping Effects in p-Terphenyl Molecular Crystals

High-quality pentacene-doped p-terphenyl bulk crystals were grown by the selective self-seeding vertical Bridgman technique (SSVBT). The lattice structure and crystal properties of the samples of different doping concentrations and their relations with p-terphenyl single crystals were tested and analyzed. The doping effects of pentacene doping at different concentrations in p-terphenyl molecular crystals are discussed. The powder X-ray diffraction, FTIR, and 1H NMR studies show that no additional peaks (except for p-terphenyl) are observed in the spectra of two doped crystals. The results indicate that guest molecules appear as defects in the form of irregularly oriented molecules which do not significantly change the crystal structures. As the doping concentration increases, the average crystallite size decreases, and the crystallinity declines. The ultraviolet–visible absorption and fluorescence spectra show that with added pentacene molecules, the characteristic peak intensities decrease in the spectra owing to the p-terphenyl molecular transition. Meanwhile, characteristic peaks appear due to the pentacene molecular transition. Moreover, with the increase of doping concentration, the intensities of characteristic peaks of host molecules decrease continuously, and those of guest molecules increase accordingly.

Improving the nonlinear electro-optical responses of doped nematic liquid crystals with chiral dopants

Liquid crystals with considerable optical and electro-optical responses play important roles in photonics and optoelectronics. In this research, the electro-optical responses of pure and doped nematic liquid crystal with left-handed S-1011 chiral dopant with different percentages were investigated at different temperatures for the first time. According to the results, nematic liquid crystal with 4 wt% of chiral dopant indicates high electro-optical Kerr constat and third-order nonlinear susceptibility. In this case, various molecular interactions enhance the average order of nematic liquid crystal. By increasing the temperature, gradually the Kerr constant is deecreased, but this decreasing is slow for liquid crystal with 9 wt% of chiral dopant. Moreover, the temperature dependence of Kerr constant was used for calculating the pre-transition temperature. Therefore, these results provide a precise and simple method for improving the electro-optical responses of a nematic liquid crystal, which is an important step in the design of optoelectronic devices.

Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime

Rare-earth doped crystals have long coherence times and the potential to provide quantum interfaces between microwave and optical photons. Such applications benefit from a high cooperativity between the spin ensemble and a microwave cavity---this motivates an increase in the rare-earth ion concentration which in turn impacts the spin coherence lifetime. We measure spin dynamics of two rare-earth spin species, $^{145}\mathrm{Nd}$ and Yb, doped into ${\mathrm{Y}}_{\text{2}}{\mathrm{SiO}}_{\text{5}}$, coupled to a planar microwave resonator in the high-cooperativity regime, in the temperature range $1.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to $14\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. We identify relevant decoherence mechanisms, including instantaneous diffusion arising from resonant spins and temperature-dependent spectral diffusion from impurity electron and nuclear spins in the environment. We explore two methods to mitigate the effects of spectral diffusion in the Yb system in the low-temperature limit, first, using magnetic fields of up to 1 T to suppress impurity spin dynamics and, second, using transitions with low effective $g$ factors to reduce sensitivity to such dynamics. Finally, we demonstrate how the ``clock transition'' present in the $^{171}\mathrm{Yb}$ system at zero field can be used to increase coherence times up to ${T}_{2}=6(1)\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$.

Impact of Br-doping on the optical and optoelectronic properties of CsPbCl3 crystals

The all-inorganic halide perovskite CsPbX3 (X = I, Br and Cl) with outstanding optoelectronic properties and is expected to be the next generation of optoelectronic detection materials. However, the CsPbCl3 crystal is difficult to grow by low-temperature solution method. Here, we report a series of Br-doped CsPbCl3 crystals by Vertical Bridgman method. Crystal structure, spectra properties and photoelectric performances of CsPbCl3-xBrx single crystals were studied systematically. Photoluminescence (PL), X-ray excited luminescence (XEL) and UV–vis spectra can be tuned by Br-doped in the CsPbCl3 crystals. Furthermore, the basic photoelectric properties were investigated for Br-doped CsPbCl3 crystals and the optimum component of CsPbBr2.64Cl0.36 crysatal displays the highest resistivity of 2.8 × 109 Ω cm, and an on/off ratio of ∼ 25. Our work provides a feasible strategy for optimizing the photoelectric properties of doped halide perovskite crystal.

Terahertz time-domain spectroscopic ellipsometry of metallic strontium titanate

The coexistence of the polar instability and metallic conduction has attracted much attention. Ferroelectric soft optic modes and carrier electrons were investigated in A- and B-site heterovalent doped strontium titanate SrTiO3 crystals by the terahertz time-domain spectroscopic ellipsometry. The observed real and imaginary parts of a complex dielectric constant were fitted by the damped harmonic oscillator model for the ferroelectric soft optic mode and the Drude-Smith model for carrier electrons. The observed soft mode frequency increases as the La and Nb content increases. It is found that the square of the ferroelectric soft mode frequency linearly changes to the carrier electron concentration. This fact indicates that the carrier electrons suppress the ferroelectric instability and the ferroelectric soft mode frequency increases as the carrier concentration increases.

Photoconductivity of pure and rare-earth doped p-GaSe single crystals

Photoconductivity characteristic of undoped and gadolinium (Gd)/dysprosium (Dy) co-doped layered [Formula: see text]-GaSe semiconductor has been experimentally investigated. A model is proposed to explain the obtained results. The creating possibility of multi-band photo-detectors with stable and reproducible parameters is shown and characteristics based on single crystals of [Formula: see text]-GaSe are activated with mentioned rare-earth ions with concentration of [Formula: see text] at.%.

Fabrication of Ga2O3 Schottky Barrier Diode and Heterojunction Diode by MOCVD.

In this article, we reported on a Ga2O3-based Schottky barrier diode and heterojunction diode from MOCVD. The Si-doped n-type Ga2O3 drift layer, grown by MOCVD, exhibited high crystal quality, flat surfaces, and uniform doping. The distribution of unintentional impurities in the films was studied. Then nickel Schottky barrier diode and p-NiO/n-Ga2O3 heterojunction diode were fabricated and measured. Without any electric field management structure, the Schottky barrier diode and heterojunction diode have specific resistances of 3.0 mΩ·cm2 and 6.2 mΩ·cm2, breakdown voltages of 380 V and 740 V, thus yielding power figures of merit of 48 MW·cm-2 and 88 MW·cm-2, respectively. Besides, both devices exhibit a current on/off ratio of more than 1010. This shows the prospect of MOCVD in power device manufacture.

Growth, geometrical analysis, FMO, MEP UV–vis, nonlinear optical and antibacterial properties of pure and 2-furoic acid doped Guanidinium carbonate single crystal

In the presence of distilled water, the adaption of the slow evaporation solution growth approach resulted in the successful development of single crystals of Pure and doped GC (FAGC). The cell characteristics of the produced FAGC crystals were investigated using single-crystal X-ray diffraction analysis. The theoretical analysis was carried out using the DFT method, and the HOMO-LUMO energy band difference was estimated. The Molecular optimized geometry, MEP and HOMO-LUMO energy distance were computed using the B3LYP level of theory using a 6-31G (d,p) basis set. The FT-IR spectrum probes the modes of vibration of various functional groups in pure and doped GC (FAGC) crystals. According to UV–visible NIR transmittance experiments, the formed crystal exhibits a high transmittance in the whole visible range. The relative SHG efficiency of pure and doped crystals (FAGC) was carried out by the Kurtz perry technique. The Antibacterial activity demonstrates that both the pure and the dopant have antibacterial action against dangerous microorganisms.

Dilution of the magnetic lattice in the Kitaev candidate α−RuCl3 by Rh3+ doping

Magnetic dilution of a well-established Kitaev candidate system is realized in the substitutional ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{Cl}}_{3}$ series $(x=0.02--0.6)$. Optimized syntheses protocols yield uniformly doped single crystals and polycrystalline powders that are isostructural to the parental $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ as per x-ray diffraction. The Rh content $x$ is accurately determined by the quantitative energy-dispersive x-ray spectroscopy technique with standards. We determine the magnetic phase diagram of ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{Cl}}_{3}$ for in-plane magnetic fields from magnetization and specific-heat measurements as a function of $x$ and stacking periodicity and identify the suppression of the magnetic order at $x\ensuremath{\approx}0.2$ towards a disordered phase, which does not show any clear signature of freezing into a spin glass. Comparing with previous studies on the substitution series ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{Cl}}_{3}$, we propose that chemical pressure would contribute to the suppression of magnetic order, especially in ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{Cl}}_{3}$, and that the zigzag magnetic ground state appears to be relatively robust with respect to the dilution of the Kitaev-$\mathrm{\ensuremath{\Gamma}}$-Heisenberg magnetic lattice. We also discovered a slight dependence of the magnetic properties on thermal cycling, which would be due to an incomplete structural transition.

Versatile iodine-doped BiOCl with abundant oxygen vacancies and (110) crystal planes for enhanced pollutant photodegradation

Crystal plane regulation, defect engineering, and element doping can effectively solve the problems of large band gaps, poor light absorption, and fast recombination of BiOCl. In this work, iodine-doped BiOCl (I/BiOCl) nanowafers with abundant (110) crystal planes and oxygen vacancies (OV) were prepared by a simple hydrothermal method and assessed for pollutant photodegradation. I/BiOCl with a molar ratio of I to Cl of 0.6 (I0.6/BiOCl) degraded under visible light 95.8% of the toxic dye rhodamine B and 85.1% of the persistent antibiotic tetracycline in 5 and 10 min, respectively. In comparison, unmodified BiOCl photodegraded only between 42.0% and 48.2% of these critical water pollutants. Furthermore, I0.6/BiOCl was highly stable with most of its photocatalytic activity remaining after 4 cycles. Three reasons explain the excellent photodegradation properties of I0.6/BiOCl. First, the doped photocatalyst grew abundant (110) crystal planes, which inhibits the recombination of photogenerated electron-hole pairs. Second, the large quantity of OV present in I0.6/BiOCl increased active sites for reactive oxygen species generation, improved photogenerated charge separation, and pollutants adsorption. Lastly, I0.6/BiOCl had a modified electronic band structure enhancing light absorption. Overall, these results describe a promising photocatalyst capable of degrading efficiently major pollutants with different structures.