GaP Crystals Research Articles

Cartesian light: Unconventional propagation of light in a three-dimensional superlattice of coupled cavities within a three-dimensional photonic band gap

We explore the unconventional propagation of light in a three-dimensional (3D) superlattice of coupled resonant cavities in a 3D photonic band gap crystal. Such a 3D cavity superlattice is the photonic analogue of the Anderson model for spins and electrons in the limit of zero disorder. Using the plane-wave expansion method, we calculate the dispersion relations of the 3D cavity superlattice with the cubic inverse woodpile structure that reveal five coupled-cavity bands, typical of quadrupole-like resonances. For three out of five bands, we observe that the dispersion bandwidth is significantly larger in the $(k_x, k_z)$-diagonal directions than in other directions. To explain the directionality of the dispersion bandwidth, we employ the tight-binding method from which we derive coupling coefficients in 3D. For all converged coupled-cavity bands, we find that light hops predominantly in a few high-symmetry directions including the Cartesian $(x, y, z)$ directions, therefore we propose the name "Cartesian light". Such 3D Cartesian hopping of light in a band gap yields propagation as superlattice Bloch modes that differ fundamentally from the conventional 3D spatially-extended Bloch wave propagation in crystals, from light tunneling through a band gap, from coupled-resonator optical waveguiding, and also from light diffusing at the edge of a gap.

Photo-Sensitive Pb5S2I6 crystal incorporated polydopamine biointerface coated on nanoporous TiO2 as an efficient signal-on photoelectrochemical bioassay for ultrasensitive detection of Cr(VI) ions

An ultrasensitive Visible light-triggered photoelectrochemical (PEC) sensor was designed based on ideal photoactive lead sulfoiodide (Pb5S2I6) as low band gap crystal, which hydrothermally synthesized rapidly at low temperature (160 °C) in hydrochloride acid media followed by its incorporation into polydopamine as reactive photo-biointerface, through a facile in situ electropolymerization method, coated on nanoporous TiO2 grown by anodization on Ti foil. The structure of as-prepared samples and their photoelectrochemical properties were fully characterized. This unique photo-sensitive Pb5S2I6 catalyst-based PEC bioassay was constructed for the detection of low-abundant Cr(VI) ion in real samples. Applying central composite design, individual and mutual interaction effects were evaluated to obtain optimized solution pH, applied potential and radiant light wavelength as operational factors influencing the PEC efficiency for Cr(VI) detection. At optimal condition, the proposed sensor due to effective suppress in electron–hole recombinations showed a very low detection limit of 3.0 nM, over a broad linear concentration range of 0.01–80 μM in addition to high sensitivity versus 1.9 μA/μM Cr(VI). Proposed PEC sensor displayed high selectivity, reproducibility and stability as well as improved excitation conversion efficiency, which make it highly applicable using solar energy. The potential applicability of the designed sensor was evaluated in water, tomato juice and hair color.

Three-dimensional structure of antiphase domains in GaP on Si(0 0 1)

Antiphase domains are three-dimensional crystal defects commonly arising at the interface of III–V semiconductors and Si. While control over their formation has been achieved, the geometry of the antiphase domain itself that is separated from the mainphase of the crystal by the so-called antiphase boundary, has not yet been fully understood. In this work, we first investigate the interface between GaP and Si itself by cross-sectional scanning tunneling microscopy (XSTM) to reveal possible intermixing within an 8 monolayers wide region. Furthermore, we present an extensive analysis combining transmission electron microscopy and XSTM to elucidate the shape of antiphase domains in GaP. To create a true-to-scale, three-dimensional model of an antiphase domain, firstly, plan-view transmission electron microscopy images are drawn on. Subsequently, the progression of many antiphase boundaries through the GaP crystal as viewed from the (1 1 0) and (1 0) cleavage planes is analyzed all the way down to the atomic level by means of XSTM. This enables a detailed analysis of the shape and physical dimensions of the antiphase domains. A typical measured extension in growth directions is found to be a maximum of 60 nm and the maximum measured extension of the base plane in [ 1 0] and [1 1 0] directions is about 160 nm and 50 nm, respectively. They appear as pyramids with anisotropic base planes whose side facets kink many times.

Three-dimensional photonic band gap cavity with finite support: Enhanced energy density and optical absorption

We study numerically the transport and storage of light in a 3D photonic band gap crystal doped by a single embedded resonant cavity. The crystal has finite support since it is surrounded by vacuum, as in experiments. Therefore, we employ the finite element method to model the diamond-like inverse woodpile crystal that consists of two orthogonal arrays of pores in a high-index dielectric such as silicon and that has experimentally been realized by CMOS-compatible methods. A point defect that functions as the resonant cavity is formed in the proximal region of two selected orthogonal pores with a radius smaller than the ones in the bulk of the crystal. We present a field-field cross-correlation method to identify resonances in the finite-support crystal with defect states that appear in the 3D photonic band gap of the infinite crystal. Out of 5 observed angle-independent cavity resonances, one is s-polarized and 4 are p-polarized for light incident in the X or Z directions. It is remarkable that quality factors up to Q = 1000 appear in such thin structures (3 unit cells). We find that the optical energy density is remarkably enhanced at the cavity resonances by up to 2400x the incident energy density in vacuum or up to 1200x the energy density of the equivalent effective medium. We find that an inverse woodpile photonic band gap cavity with a suitably adapted lattice parameter reveals substantial absorption in the visible range. Below the 3D photonic band gap, Fano resonances arise due to interference between the discrete fundamental cavity mode and the continuum light scattered by the photonic crystal. We argue that the five eigenstates of our 3D photonic band gap cavity have quadrupolar symmetry, in analogy to d-like orbitals of transition metals. We conclude that inverse woodpile cavities offer interesting perspectives for applications in optical sensing and photovoltaics.

Високотемпературні сенсори деформації на основі ниткоподібних кристалів фосфіду галію

The paper presents a study of tensoresistive characteristics of p-type GaP whiskers with [111] crystallographic orientation coinciding with the direction of the maximal piezoresistive effect for this material. The authors present a newly-developed technology of creating the ohmic contacts to GaP crystals that allows using these crystals at high temperatures (400—600°C). Tensoresistive characteristics of p-type GaP whiskers were studied in the strain range of ±1,2•10–3 rel. un. These studies show that the gauge factor for these crystals at 20°C is rather large. Thus, for p-type GaP crystals with a resistivity of 0.025—0.03 Ω•cm, the gage factor is in the range of 90—95. The study of tensoresistive properties shows that in the temperature range of 20—300°C for p-type GaP crystals with the resistivity of 0,01—0,03 Ω•cm, the gage factor decreases as the temperature rises, but in the temperature range of 300—550°C for this crystals, very slight temperature dependence of the gage factor was observed. In this temperature range, the temperature coefficient of gage factor is no more than –0,03%/°Ñ. In the temperature range of 300—500°C, the value of gage factor is high (40—50). It could be noticed that in the entire investigated temperature range, the strain sensors based on p-type GaP whiskers have the linear resistance vs. strain dependence in the strain range of ±5,0•10–4 rel. un. The developed strain sensors based on p-type GaP whiskers have high mechanical strength at the static and dynamic strain (more than 108 cycles), which makes them operable in dynamic mode.

Measuring effective electro-optic coefficient at 1040 nm by spectral intensity modulation with THz time-domain spectroscopy

We report a single method for measuring the effective electro-optics (EO) coefficient only by spectral intensity modulation with a terahertz time-domain spectroscopy (THz-TDS) device. Compared with conventional methods, the measuring device based on THz-TDS by probing the spectral intensity modulation is simple, rapid, and highly sensitive. It does not require special preparation process, electrode contact or applying high voltage on the sensor samples. The EO coefficients of four kinds of materials, namely, ZnTe and GaP crystals, DAST wafer and GaSe film, are measured at 1040 nm. The results showed good agreement with literature data by the conventional methods.

Optical rectification of a 100 W average power mode-locked thin-disk oscillator.

We demonstrate terahertz (THz) generation at megahertz repetition rate by optical rectification in GaP crystals, using excitation average power levels exceeding 100 W. The laser source is a state-of-the-art diode-pumped Yb:YAG SESAM-mode-locked thin-disk laser, capable of generating 580 fs pulses at an average power up to 120 W and a repetition rate of 13.4 MHz directly from a one-box oscillator, without the need for any extra amplification stages. In this first demonstration, we measure a maximum THz average power of 78 μW at a central frequency of 0.8 THz. Our results show that optical rectification of state-of-the-art high average power ultrafast sources in nonlinear crystals is within reach and paves the way toward high average power, ultrafast laser pumped THz sources.

Structural, optical, electrical and thermal characteristics of La{CS(NH2)2CO(NH2)2}Cl3 : A novel hybrid complex for optoelectronic applications

A hybrid complex of lanthanum chloride with urea and thiourea is crystallized at room temperature by conventional solution method. The structural investigations by single crystal X-ray diffraction confirmed the orthorhombic system with cell dimensions a = 7.676 Å, b = 8.564 Å, c = 5.498 Å, α = β = γ = 90°. The optical studies by UV–VIS absorption spectroscopy shows the complex exhibits transmittance about 96%. The complex is characterized as the wide band gap crystals with value greater than 4 eV. The dielectric properties were studied in frequency range 10 kHz–1 MHz in temperature range 303–453 K. The ac conductivity was found to obey the universal power law and suggests the correlated barrier hoping mechanism dominating the conduction process. The thermal stability and the decomposition mechanism were confirmed by thermo gravimetric and differential thermo analytical (TG/DTA) techniques.

The use of DSTMS crystal for broadband terahertz electro-optic sampling based on laser pulse amplitude changes

Application of the organic crystal 4-N,N-dimethylamino-4′-N′-methylstilbazolium 2,4,6-trimethylbenzenesulfo-nate (DSTMS) for electro-optic time-domain measurements of terahertz wave radiation generated by two-color air discharge is experimentally approbated. Measurements were done with the use of techniques based on laser pulse energy changes in a DSTMS crystal. The results demonstrate that the measured signal has a bandwidth entirely covering the terahertz band (wider than 10 THz at a 0.1 amplitude level for 50 fs laser pulses) and significantly overcomes the value of the signal given by the standard detection technique with a GaP crystal.

Broadband terahertz pulse generation driven by an ultrafast thin-disk laser oscillator.

We demonstrate broadband THz generation driven by an ultrafast thin-disk laser (TDL) oscillator. By optical rectification of 50-fs pulses at 61 MHz repetition rate in a collinear geometry in crystalline GaP, THz radiation with a central frequency at around 3.4 THz and a spectrum extending from below 1 THz to nearly 7 THz are generated. We realized a spectroscopic characterization of a GaP crystal and a benchmark measurement of the water-vapor absorption spectrum in the THz range. Sub-50-GHz resolution is achieved within a 5 THz bandwidth. Our experiments show the potential of ultrafast TDL oscillators for driving MHz-repetition-rate broadband THz systems.

THz generation from DFG in a noncollinear phase-matched GaP crystal pumped with a compact diode-pumped two-frequency LiYF4:Nd laser

Pumping with a nanosecond two-frequency compact diode-pumped LiYF4:Nd laser emitting at 1047 and 1053 nm, a THz wave has been produced in a GaP crystal, attributed to the difference frequency generation process $$\frac{1}{{{\lambda _3}}} - \frac{1}{{{\lambda _2}}}=\frac{1}{{{\lambda _{{\text{TH}}z}}}}$$ . In a first set-up, the two pumping beams had a tunable angular separation provided by a sapphire prism. The phase matching angle of the noncollinear interaction has been determined to be 0.202° external angle and the refractive index 3.377 at 1.6 THz. The angular acceptance was rather broad, due to the fact that the thickness of the nonlinear crystal was only 3 mm. With a second set-up using a beam displacer constituted by YVO4 plates of different thicknesses, smaller angular separations were explored under other directions of polarizations of the pump beams. Because at the three wavelengths involved in this study the velocity of the nonlinear polarization wave inside GaP is higher than the THz wave phase velocity, a Cerenkov phase matching is possible. The plane-wave calculations show that the THz radiation under this process exits from the output face of the crystal, as it is experimentally observed.

Three-octave terahertz pulses from optical rectification of 20 fs, 1 μm, 78 MHz pulses in GaP

We demonstrate optical rectification of 1 μm pulses with a duration of 20 fs, a repetition-rate of 78 MHz and an average power of 5.5 W, in a 2 mm thick GaP crystal. The spectrum of the resulting far-infrared pulses is centered at 1.5 THz and extends to 5 THz at −50 dB intensity. In the absence of resonant absorption of GaP in this range, the spectrum has a well-behaved shape, facilitating spectroscopic applications. In the context of the recent rapid evolution of high-power Yb-based femtosecond laser systems, these results show a viable route towards sources of THz pulses combining broad bandwidth, high average power and a smooth spectral shape.

Growing compound semiconductors

Materials Science Epitaxial growth is the main technique used for depositing nonsilicon integrated electronic and photonic devices. However, methods for growing devices on amorphous and nonepitaxial substrates are limited. Sarkar et al. overcome this by using standing evaporation or sputtering techniques to deposit a metal, such as indium, with a capping oxide layer. The metal is heated in a hydrogen environment, and a precursor is added to convert the metal to the desired target, such as InP, under conditions where only a single nucleation site forms in each patterned site. The versatility of the method is demonstrated through the growth of InP, GaP, InAs, InGaP, SnP, and Sn4P3 crystals directly on SiO2, Si3N4, TiO2, Al2O3, Gd2O3, SrTiO3, and graphene. ACS Nano 10.1021/acsnano.8b01819 (2018).

Electro-optic sampling of optical pulses and electron bunches for a compact THz-FEL source

A systematic one dimensional analytical model describing the full electromagnetic propagation in electro-optic (EO) diagnostic is proposed and designed for a terahertz FEL source at HUST. Our model contains two main aspects: the propagation of the THz pulse (1.5–6 THz) along the transport line and the THz EO process in the detection crystal. The diffraction, Fabry–Perot and focusing effects are included in the THz propagation process. The phase mismatch, the frequency-dependent EO coupling coefficient and geometrical overlap between probe and THz pulses as well as the group velocity dispersion and finite duration of the probe pulse are considered in the THz EO process. The calculation shows that the diffraction in the TPX window and the Fabry–Perot effect in the GaP crystal are crucial for retrieving the details of the THz optical pulse. While for electron bunches, the detected Coulomb electric field will be significantly broadened due to the relatively low relativistic Lorenz factor (γ=10–20). Therefore, a convenient deconvolution algorithm is utilized to reconstruct THz electric field from the distorted EO signals, where the truncated singular value decomposition method is employed. Our algorithm is verified to work well even with a low signal-to-noise ratio (20 dB) in the future measurement.

Finite-size Scaling of the Density of States in Photonic Band Gap Crystals.

The famous vanishing of the density of states (DOS) in a band gap, be it photonic or electronic, pertains to the infinite-crystal limit. In contrast, all experiments and device applications refer to finite crystals, which raises the question: Upon increasing the linear size L of a crystal, how fast does the DOS approach the infinite-crystal limit? We present a theory for finite crystals that includes Bloch-mode broadening due to the presence of crystal boundaries. Our results demonstrate that the DOS for frequencies inside a band gap has a 1/L scale dependence for crystals in one, two and three dimensions.

Design and analysis of novel microstrip patch antenna on photonic crystal in THz

Recent advancement of communication system requires low cost, minimal weight, low profile and high-performance antenna to execute the demand of the future realization. A high gain novel microstrip patch antenna design is proposed, based on the photonic crystal for terahertz (THz) spectral band applications. This antenna is mounted on polyimide substrate that employs Photonic Band Gap (PBG) crystal and the Gain of 7.934 dB, Directivity 8.612 dBi and VSWR close to unity at resonant frequency of 0.6308 THz. The proposed antenna model is compared with homogeneous polyimide substrate structure based microstrip patch antenna and analyzed the radiation characteristics. Moreover, the performance of designed antenna is investigated with different PBG cylindrical distance, PBG hole radius, curvature radius of patch and substrate heights. The projected design antenna has a bandwidth of 36.25 GHz and −10 dB impedance with operating frequency range varying from 0.6152 THz to 0.6514 THz, hence it can be utilized for detection of explosive and material characterization applications.

Electronic structure of the dilute magnetic semiconductor Ga1−xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission

We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) $\mathrm{G}{\mathrm{a}}_{0.98}\mathrm{M}{\mathrm{n}}_{0.02}\mathrm{P}$ and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between $\mathrm{G}{\mathrm{a}}_{0.98}\mathrm{M}{\mathrm{n}}_{0.02}\mathrm{P}$ and GaP in both angle-resolved and angle-integrated valence spectra. The $\mathrm{G}{\mathrm{a}}_{0.98}\mathrm{M}{\mathrm{n}}_{0.02}\mathrm{P}$ bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of $\mathrm{G}{\mathrm{a}}_{0.97}\mathrm{M}{\mathrm{n}}_{0.03}\mathrm{As}$ and GaAs [Gray et al., Nat. Mater. 11, 957 (2012)], demonstrating the strong similarity between these two materials. The Mn $2p$ and $3s$ core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.

Terahertz Spectrum Measurement of Corrosion Products on Coated Steel Sheet Surface

Our research group has developed a terahertz light source with high luminance and broadband, and is developing research on non-destructive inspection technology. As a nondestructive inspection technology for hot-dip galvanized steel sheets, we have built a terahertz spectrum database for corrosion products that may exist there. In this research, we aim to newly obtain spectral data of β-FeOOH. Absorption Spectrum is shown in Figure.1. Optical system is shown in Figure.2. The terahertz wave was generated by difference frequency mixing using a GaP crystal which is a nonlinear optical crystal. The standard powder sample was diluted with polyethylene powder and pelletized, and it was measured at room temperature by a permeation method. As a result of spectroscopic measurement, an absorption peak was obtained around 3.06 THz. On the day of the presentation, in addition to discussions on attribution of peaks, report together with ATR-FTIR results. Figure 1

Features of the Percolation Scheme of Vibrational Spectrum Reconstruction in the Ga1 – xAl x P Alloy

Specific features of the properties of Ga–P lattice vibrations have been investigated using the percolation model of a mixed Ga1 – xAl x P crystal (alloy) with zero lattice mismatch between binary components of the alloy. In contrast to other two-mode alloy systems, in Ga1 – xAl x P a percolation splitting of δ ~ 13 cm–1 is observed for the low-frequency mode of GaP-like vibrations. An additional GaP mode (one of the percolation doublet components) split from the fundamental mode is observed for the GaP-rich alloy, which coincides in frequency with the gap corresponding to the zero density of one-phonon states of the GaP crystal. The vibrational spectrum of impurity Al in the GaP crystal has been calculated using the theory of crystal lattice dynamics. Upon substitution of lighter Al for the Ga atom, the calculated spectrum includes, along with the local mode, a singularity near the gap with the zero density of phonon states of the GaP crystal, which coincides with the mode observed experimentally at a frequency of 378 cm–1 in the Ga1 – xAl x P (x < 0.4) alloy.

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.