GaSe Crystals Research Articles

Optical Spectra of GaSe and GaS Crystals of Different Thicknesses

The transmission spectra of GaSe and GaS crystals of different thicknesses prepared by mechanical stratification of bulk crystals have been investigated. The quantum-size shifts of exciton resonances in thin GaSe samples are as high as 12 meV, which is close to the exciton binding energy. The high-energy interband transitions in GaSe and GaS are observed near 3.4 and 3.7 eV, respectively.

Sum-frequency generation of Q-switched CO laser radiation in BaGa2GeSe6 and GaSe nonlinear crystals

Sum-frequency generation of multiline Q-switched CO laser radiation is studied in the BaGa2GeSe6 (BGGSe) crystal and in the GaSe crystal. The maximal external conversion efficiency obtained in the BGGSe crystal is 0.7%, which corresponded to the internal conversion efficiency of 1% taking into account optical losses under reflection from uncoated facets of the crystal. The maximum external conversion efficiency in the GaSe crystal is 0.15% with internal efficiency 0.31%. Effective nonlinearity of BGGSe crystal is determined through the ratio between measured efficiency in BGGSe and GaSe crystals. Effective nonlinearity for sum-frequency generation of the CO laser emission in the BGGSe crystal is deff = 42 ± 14 pm/V, and nonlinear coefficient of this crystal is d11 = 49 ± 15 pm/V.

Frequency and Thermal Behavior of Acoustic Absorption in ε-GaSe Crystals

The paper presents results of measuring acoustic absorption in e-GaSe crystals. The absorption of a longitudinal wave which propagates normal to the crystal layers, quadratically depends on frequency. However, it does not depend on temperature, i.e. it displays an Akhiezer behavior although its absolute value considerably exceeds the expected. The analysis of the frequency and thermal behavior of absorption of piezoelectric waves propagating along the layers, includes the deduction of contribution made by the interaction between waves and charge carriers. This analysis shows the linear dependence between the lattice absorption of these waves and the frequency. The linear frequency and weak temperature dependences of the acoustic absorption characterize the additional ultra-Akhiezer absorption in glasses. In our case, it can be caused by various polytypes forming in GaSe crystals which differ merely in a mutual arrangement of layers.

Analysis of the specific vibration modes of goethite (α-FeOOH) by terahertz spectroscopy and calculations of the vibration frequencies of a single molecule using density functional theory

Steel sheet with an insulator to prevent corrosion is used for various purposes including in building and car manufacture. Terahertz waves, for which insulators are highly permeable and metal surfaces are highly reflective, have been studied in order to establish a new inspection technology for these steel plates. In our previous research, spectroscopic measurements in the 1.0-4.0 THz range, generated by a GaP crystal, were carried out in order to collect information on the infrared activity of the metal corrosion products formed on Zn-Al hot-dip galvanized steel sheet. In the previous work, the infrared activity of Fe-based corrosion products was not examined. To examine these products, we conducted THz spectroscopy on goethite (α-FeOOH) in the range from 8.4 to 11.0 THz, generated by a GaSe crystal. The results of Attenuated Total Reflectance (ATR) FTIR spectral measurements and molecular vibration calculations were analyzed, on the basis of which the natural vibration modes of α-FeOOH in the THz frequency range were assigned.

High-Quality GaSe Single Crystal Grown by the Bridgman Method.

A high-quality GaSe single crystal was grown by the Bridgman method. The X-ray rocking curve for the studied GaSe sample is symmetric and the Full Width at Half Maximum (FWHM) is only 46 arcs, which is the smallest value ever reported for GaSe crystals. The IR-transmittance is about 66% in the range from 500 to 4000 cm−1. The photoluminescence spectrum at 9.2 K shows a symmetric and sharp excition peak in 2.1046 eV. The results indicate that the as-grown GaSe crystal is of high crystalline quality. The as-grown -GaSe crystal has a p-type conductance with the resistivity of 103 Ω/cm, and the Hall mobility is ~25 cm2 V−1 s−1. Few-layer GaSe crystals were prepared through mechanical exfoliation from this high-quality crystal sample. Few-layer GaSe-based photodetectors were fabricated, which exhibit an on/off ratio of 104, a field-effect differential mobility of 0.4 cm2 V−1 s−1, and have a fast response time less than 60 ms under light illumination.

Оптические спектры кристаллов GaSe и GaS различной толщины

AbstractThe transmission spectra of GaSe and GaS crystals of different thicknesses prepared by mechanical stratification of bulk crystals have been investigated. The quantum-size shifts of exciton resonances in thin GaSe samples are as high as 12 meV, which is close to the exciton binding energy. The high-energy interband transitions in GaSe and GaS are observed near 3.4 and 3.7 eV, respectively.

Compact and stable high-repetition-rate terahertz generation based on an efficient coaxially pumped dual-wavelength laser.

A compact and stable terahertz (THz) source is demonstrated based on difference frequency generation (DFG) pumped by an efficient dual-wavelength acousto-optic (AO) Q-switched solid-state Nd:YLF laser with composite gain media (a-cut and c-cut) in the coaxial pumping configuration. Optimal power ratio and pulse synchronization of the orthogonal polarized 1047/1053 nm dual-wavelength laser could be realized by varying the pump focusing depth and/or pump wavelength. The total power of 2.92 W was obtained at 5 kHz pumped by 10-W laser-diode power at 803 nm. Such an efficient dual-wavelength laser demonstrated good stability and inconspicuous timing jitter benefiting from the suppressed gain competition between two resonating wavelengths. An 8-mm-long GaSe crystal was employed to generate THz waves at 1.64 THz by DFG and the maximum THz average output power was about 0.93 μW. This compact coaxial pumping method can be extended to all kinds of neodymium (Nd) doped laser crystals to produce different dual-wavelength lasers for various THz wavelength generation, which have good prospects for portable and costless applications like imaging, non-destructive inspection, etc.

Optical Properties of Boron-Doped Gallium Selenide

The electronic-absorption and luminescence spectra and the kinetics of relaxation of photocurrent in GaSe single crystals and thin films doped with boron atoms are experimentally investigated. Crystals are doped either in the course of synthesis or upon growing single crystals by the Bridgman method. Thin GaSe films are obtained by thermal evaporation of the compound preliminarily doped with boron. An absorption band with the maximum at λ = 925 nm, which is attributed to boron contaminations, is revealed from the comparison of the electronic-absorption spectra of a GaSe crystal and thin films doped with boron. When the crystals are excited with Nd:YAG laser pulses of a duration of 12 ns, it is established that recombination of nonequilibrium current carriers in pure crystals occurs through rapid and slow recombination channels and in crystals doped with boron only through rapid channels. In the region near λ = 932 nm, photoluminescence is observed in the crystals doped with boron, and its half-bandwidth is 15 A.

Effect of adding Te to layered GaSe crystals to increase the van der Waals bonding force

The interplanar binding strength of layered GaSe1-xTex crystals was directly measured using a tensile testing machine. The GaSe1-xTex crystals were grown by a low temperature liquid phase solution method under a controlled Se vapor pressure. The stoichiometry-controlled GaSe1-xTex crystal has the ε-polytype structure of GaSe, where the Te atoms are substituted for some of the Se atoms in the GaSe crystal. The effect of adding Te on the bonding strength between the GaSe layers was determined from direct measurements of the van der Waals bonding energy. The bonding energy was increased from 0.023 × 106 N/m2 for GaSe to 0.16 × 106 N/m2 for GaSe1-xTex (x = 0.106).

Phase-locked multi-terahertz electric fields exceeding 13 MV/cm at a 190 kHz repetition rate.

We demonstrate a compact source of energetic and phase-locked multi-terahertz pulses at a repetition rate of 190kHz. Difference frequency mixing of the fundamental output of an Yb:KGW amplifier with the idler of an optical parametric amplifier in GaSe and LiGaS2 crystals yields a passively phase-locked train of waveforms tunable between 12 and 42THz. The shortest multi-terahertz pulses contain 1.8 oscillation cycles within the intensity full width at half-maximum. Pulse energies of up to 0.16μJ and peak electric fields of 13MV/cm are achieved. Electro-optic sampling reveals a phase stability better than 0.1π over multiple hours, combined with free carrier-envelope phase tunability. The scalable scheme opens the door to strong-field terahertz optics at unprecedented repetition rates.

Broadband and narrowband terahertz generation and detection in GaSe1−xSx crystals

Terahertz wave generation through optical rectification of femtosecond laser pulses and its detection in GaSe and GaSe1−xSx crystals with a relatively low (x = 0.04) and high (x = 0.29) content of sulfur was studied. The decrease of terahertz generation and detection efficiency at an increase of sulfur content in GaSe1−xSx was observed. The phase-matching conditions for electro-optical sampling in GaSe and GaSe1−xSx crystals were analyzed. The arising possibility to achieve the narrowing of terahertz detection bandwidth using thicker GaSe crystals was experimentally confirmed.

Enhancing the blue shift of SHG signal in GaSe:B/Ce crystal

The influence of Ce3+ on the wavelength of second harmonic generation (SHG) signal in boron doped GaSe crystals have been investigated. We found that by substitution of Ce3+ with B3+, SHG signal shifted to lower wavelength. In addition, the nonlinear absorption (NA) properties and ultrafast dynamics of pure, 1at.% B3+ and 0.5at.% B3++0.5at.% Ce3+ doped GaSe crystals have been studied by open aperture Z-scan and ultrafast pump probe spectroscopy techniques. From the open aperture Z-scan experiments we observed that all of the crystals showed nonlinear absorption (NA). However, pump-probe experiments revealed that when GaSe crystal is doped, the NA signal turns into a bleaching signal with different lifetimes depending on the type and concentration of the dopant atoms.

Growth and characterization of an Al-doped GaSe crystal

A GaSe: Al (0.13wt%) single crystal was grown using the Bridgman method combined with a crucible rotation technique. A 35×19×5.5mm3 sample was cut from the as-grown crystal ingot. The GaSe: Al (0.13wt%) crystal has an indentation hardness of 2.27GPa, which is 2.6 times harder than the pure GaSe crystal. In particular, a sample with a thickness of 5.5mm has an infrared transmission of approximately 60%. The absorption coefficient of this sample is as low as 0.1cm−1 over the range of 0.83 to −14μm, which demonstrates its high optical quality. A crystal growth method with the described procedures may be suitable to grow other doped GaSe crystals.

Characterization of Layered GaSe Crystals Intercalated with RbNO3 Ferroelectric Salt and their Application for Electric Capacitors

Characterization of Layered GaSe Crystals Intercalated with RbNO3 Ferroelectric Salt and their Application for Electric Capacitors

On-Chip Waveguide Coupling of a Layered Semiconductor Single-Photon Source.

Fully integrated quantum technology based on photons is in the focus of current research, because of its immense potential concerning performance and scalability. Ideally, the single-photon sources, the processing units, and the photon detectors are all combined on a single chip. Impressive progress has been made for on-chip quantum circuits and on-chip single-photon detection. In contrast, nonclassical light is commonly coupled onto the photonic chip from the outside, because presently only few integrated single-photon sources exist. Here, we present waveguide-coupled single-photon emitters in the layered semiconductor gallium selenide as promising on-chip sources. GaSe crystals with a thickness below 100 nm are placed on Si3N4 rib or slot waveguides, resulting in a modified mode structure efficient for light coupling. Using optical excitation from within the Si3N4 waveguide, we find nonclassicality of generated photons routed on the photonic chip. Thus, our work provides an easy-to-implement and robust light source for integrated quantum technology.

Optical and defect properties of S-doped and Al-doped GaSe crystals**Project supported by Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. CXJJ-16M128

S-doped and Al-doped GaSe crystals are promising materials for their applications in nonlinear frequency conversion devices. The optical and defect properties of pure, S-doped, and Al-doped GaSe crystals were studied by using photoluminescence (PL) and Fourier transform infrared spectroscopy (FT-IR). The micro-topography of (0001) face of these samples was observed by using scanning electron microscope (SEM) to investigate the influence of the doped defects on the intralayer and interlayer chemical bondings. The doped S or Al atoms form the or substitutional defects in the layer GaSe structure, and the positive center of could induce defect complexes. The incorporations of S and Al atoms can change the optical and mechanical properties of the GaSe crystal by influencing the chemical bonding of the layer structure. The study results may provide guidance for the crystal growth and further applications of S-doped and Al-doped GaSe crystals.

Identification of Combination Phonon Modes in Pure and Doped GaSe Crystals by THz Spectroscopy

Terahertz transmission of (i) pure gallium selenide, (ii) 500-ppm indium-doped gallium selenide, and (iii) 500-ppm chromium-doped gallium selenide is taken in the range 0.2–3.0 THz (6.67–100 cm−1 ) to identify the effect of doping on phonon modes. Fourier transform of time domain THz transmission data is fitted with a modified Drude–Smith model to derive phonon mode oscillator strength, phonon relaxation rate, plasma frequency, and momentum relaxation time of free carriers. It is observed that the effect of doping on defect states and carrier concentration rightly accounts the measured plasma frequency and momentum relaxation time. The THz absorption lines are appropriately attributed to the combination of phonon modes obtained by Raman spectroscopy.

Electrical conductivity in single crystals of GaSe x Te1 – x solid solutions in strong electrical fields

This paper presents some results of studying the Poole–Frenkel effect with allowance for shielding in layered GaSe and GaTe single crystals and their solid solutions in strong electrical fields of up to 105 V/cm at temperatures of 103–250 K. According to the relationship \(\left(\frac{\sigma}{\sigma(0)}\right)^{1/2}\) log\(\frac{\sigma}{\sigma(0)} = E\sqrt{\frac{\varepsilon}{4\pi n(0)kT}}\), there exists a linear dependence between \(\left(\frac{\sigma}{\sigma(0)}\right)^{1/2}\) log\(\frac{\sigma}{\sigma(0)}\) and the electrical field E (σ is the electrical conductivity in strong electrical fields, and σ(0) is the electrical conductivity in the ohmic region). The slopes of these lines have been determined at different temperatures (103–250 K) by estimating the concentration of current carriers n(0) = 3 × 1013–5 × 1015 cm–3 in the ohmic region of the electrical conductivity of solid solutions of layered GaSe x Te1–x single crystals (x = 1.00, 0.95, 0.90, 0.80, 0.70, 0.30, 0.20, 0.10, 0).

Liquid phase growth of GaSe1−xTex mixed crystals by temperature difference method under controlled vapor pressure

GaSe crystal is one of a group of nonlinear optical (NLO) crystals expected to be utilized as a highly efficient generators of terahertz waves. However, GaSe has some drawbacks that limit it from further application. Firstly, it has poor crystallinity and, secondly, the layers are prone to exfoliation. In this work, crystal growth was carried out at a constant low temperature under a controlled Se vapor pressure to improve the crystallinity. In addition, Te was added in order to grow mixed crystals to improve the bonding forces between the layers. X-ray fluorescence was used to measure the Te composition in the grown crystals. Red shifts of the excitation peaks were found from photoluminescence with increasing Te composition, indicating that mixed crystals were successfully grown. The lattice constant, c, was calculated from the results of X-ray diffraction and was shown to have an almost linear dependence on Te composition.

Electrical property and structural analysis of amphoteric impurity Ge doped GaSe crystal grown by liquid phase growth

In order to improve conversion efficiency of THz wave generation, Germanium (Ge)-doped gallium selenide (GaSe) single crystals have been grown by Temperature Difference Method under Controlled Vapor Pressure (TDM-CVP). In this article, electrical property and lattice constant of Ge doped GaSe (GaSe:Ge) crystal are compared with that of not-intentionally doped GaSe crystal. Compared with non-doped GaSe crystal, carrier concentration p was decreased by Ge-doping (not-intentionally doped GaSe p=3.2×1015cm−3 at 255K, GaSe:Ge p=4.9×1014cm−3 at 255K). In addition, it has been confirmed that lattice constant of GaSe crystal increased with doping Ge concentration increased.