Search

For the full benefit of the silicon chip industry and to further shift the photoresponse cut-off wavelength of the silicon photodetectors, high-performance Ag-doped Si p-n photodiodes with an extended infrared photoresponsivity are constructed on the bulk silicon wafer by a facile thermal diffusion process at 550 °C for different annealing periods of 5, 10, and 15 minutes under an argon atmosphere. These Si-compatible p-n photodiodes revealed an obvious zero-bias room temperature photoresponsivity with a threshold photon energy at a longer wavelength compared to the photoresponsivity cut-off wavelength of the commercial Si photodiode of the Hamamatsu Photonics Co (model: S2281/-04). The photoresponsivity has decreased with the annealing time increase however; the detectivity has been improved by the significant drop in leakage current and noise power. The outcomes indicate that this study paves the way for developing cost-effective Si-compatible p-n junction photodiodes, with an obvious zero-biased room-temperature photoresponsivity of a comparable intensity and longer cut-off wavelength compared to the commercial Hamamatsu Si photodiode.

This paper reports the results on fabrication methodology and photoresponse characteristics of Mg2Si0.53Ge0.47 pn-junction photodiode. At first, we have grown a Mg2Si0.53Ge0.47 single crystal with the Vertical Bridgman growth process. The grown crystal was characterized structurally and electrically by XRD, Laue, and Hall Effect measurements. XRD revealed the single-phase composition, Mg2Si0.53Ge0.47, of the grown crystal ingot. The clear Laue symmetrical diffraction pattern showed the single crystalline nature of the grown crystal. The Hall Effect measurement revealed the n-type conduction and the moderate Hall mobility (258 cm2/Vs), electrical resistivity (6.03E-02 Ω. cm), and carrier density (4.02E+17 cm-3) of the grown crystal. Such carrier density is low enough to allow depletion region formation in case of pn-junction diodes. In that sense, we have made up for the first time Mg2Si0.53Ge0.47 pn-junction photodiode by thermal diffusion of a thin Ag layer into n-Mg2Si0.53Ge0.47 substrate. The fabricated diode had an obvious rectification behavior and demonstrated a clear zero-biased photoresponse in the wavelength range from 0.95 to 1.85 μm, indicating its prominence for IR sensation in that wavelength domain.

A two-crystal, pump and probe scheme is established allowing the evaluation of potential laser materials with unknown gain and loss properties. Using a streak camera coupled to a spectrograph, the time-resolved gain or loss spectra are obtained using a probe light from an identical gain crystal. This method facilitates the evaluation of preliminary laser materials in a variety of wavelength regions. A new ultraviolet tunable amplification medium, Ce3+:LiSr0.8Ca0.2AlF6, is demonstrated to possess a broad gain spectrum of 18 nm, utilizing this newly proposed scheme.

Epitaxial growth of e-Ga2O3 is demonstrated for the first time. The e-Ga2O3 films are grown on GaN (0001), AlN (0001), and β-Ga2O3 ( 2¯01) by halide vapor phase epitaxy at 550 °C using gallium chloride and O2 as precursors. X-ray ω-2θ and pole figure measurements prove that phase-pure e-Ga2O3 (0001) films are epitaxially grown on the three kinds of substrates, although some minor misoriented domains are observed. High temperature X-ray diffraction measurements reveal that the e-Ga2O3 is thermally stable up to approximately 700 °C. The optical bandgap of e-Ga2O3 is determined for the first time to be 4.9 eV.

The first ultraviolet (UV) and visible optical isolators based on CeF3 are demonstrated. CeF3 possesses unique properties as Faraday rotator for the UV-visible wavelength region: a wide transparency range (wavelength of >300 nm) and an outstanding Verdet constant. In contrast, currently used terbium-gallium garnets and magneto-optical glasses possess a low transparency in the visible and a small Verdet constant in the UV, respectively. The optical isolator prototypes consist of a CeF3 rod, a single ring magnet, and a couple of beam splitters. The ring magnets have been designed to guarantee a homogeneous magnetic field; for it, numerical simulations have been carried out. The two prototypes are very compact and operate in the UV at 355 and in the visible at 405 nm, respectively. The performance of these devices indicates the high potential of CeF3 as a new UV-visible Faraday rotator, specially for shorter wavelengths where at present there are no optical isolators available.

Optical and lasing characteristics of a rare‐earth‐doped nonlinear crystal, neodymium‐doped lithium tantalate (Nd:LiTaO3), have been studied. Continuous wave lasing lines at 1.092 and 1.082 μm with ordinary (σ) and extraordinary (π) polarizations, respectively, have been observed by pumping near the 800 nm absorption region. The effects of annealing and poling of the crystal on the fluorescence spectrum, lifetime, and polarization are investigated. A comparative study of the slope efficiency and threshold for ordinary and extraordinary polarized lasing is also made.

The heteroepitaxial growth of ScN films was investigated on various substrates by hydride vapor phase epitaxy (HVPE). Single crystalline mirror-like ScN(100) and ScN(110) layers were successfully deposited on r- and m-plane sapphire substrates, respectively. Homogeneous stoichiometric films (N/Sc ratio 1.01 ± 0.10) up to 40 μm in thickness were deposited. Their mosaicity drastically improved with increasing the film thickness. The band gap was determined by optical methods to be 2.06 eV. Impurity concentrations including H, C, O, Si, and Cl were investigated through energy dispersive X-ray spectrometry and secondary ion mass spectrometry. As a result, it was found that the presence of impurities was efficiently suppressed in comparison with that of HVPE-grown ScN films reported in the past, which was possible thanks to the home-designed corrosion-free HVPE reactor. Room-temperature Hall measurements indicated that the residual free electron concentrations ranged between 1018–1020 cm−3, which was markedly lower than the reported values. The carrier mobility increased monotonically with the decreasing in carrier concentration, achieving the largest value ever reported, 284 cm2 V−1 s−1 at n = 3.7 × 1018 cm−3.

International audience; Optimal properties like piezoelectricity can be found in polarizable materials for which the structure changes sharply under small composition variations in the vicinity of their morphotropic phase boundary or the triple point in their isobaric temperature-composition phase diagram. In the latter, lead-free (Ba0.850Ca0.150)(Ti0.900Zr0.100)O3 ceramics exhibit outstanding piezoelectric coefficients. For the first time, we report the growth of piezoelectric lead-free single crystals in the BaTiO3-BaZrO3-CaTiO3 pseudo-ternary system. The stoichiometry control in the CaO-BaO-TiO2-ZrO2 solid solution led to single crystals with various compositions ranging from (Ba0.857Ca0.143)(Ti0.928Zr0.072)O3 to (Ba0.953Ca0.047)(Ti0.427Zr0.573)O3. We evidenced a continuous cross-over from a ferroelectric state at high titanium content to a relaxor one on increasing the zirconium content. Such a property tuning is rather seldom observed in lead-free ferroelectrics and confirms what was already reported for ceramics. Single crystal with (Ba0.838Ca0.162)(Ti0.854Zr0.146)O3 composition, which has been grown and oriented along [001] crystallographic direction, displayed electromechanical coefficients d31 and k31 of 93 pC.N−1 and 0.18, respectively, near the room temperature (T = 305 K).

Terbium is the key element for highly efficient green phosphors and visible-near IR Faraday isolators. We have recently shown the potential of LiTbF4 and Tb0.81Ca0.19F2.81 as visible Faraday rotators. In this work, we present a detail spectroscopic analysis of Tb3+ (4f8) in these two compounds with different crystal structures. By means of the Judd-Ofelt theory, the emission branching ratios and lifetimes of the Tb3+ excited states have been estimated. These results are compared with experimental values obtained for the emitting 5D4 level, as well as with the absolute light yield measurements. Tb3+ in LiTbF4 exhibits a high quantum efficiency, and its radiative lifetime is confirmed to be 7 ms. Instead, the ionic conductor Tb0.81Ca0.19F2.81, which presents a high concentration of vacant sites, shows a lower quantum efficiency and a radiative lifetime about three times larger than estimated. Absorption and emission spectra of Tb0.81Ca0.19F2.81 are broad, so that any fine structure of energy levels can be resolved. In contrast, a detailed study of the splitting of Tb3+ multiplets in Stark energy levels is carried out for LiTbF4.

Piezoelectric single-crystal ingots of Ca12Al14O33 were grown by Czochralski technique. Upon specific chemical reductions, this dielectric material can be turned into an oxygen solid electrolyte, a mixed conductor, or an electride. We followed the thermal evolution of the piezoelectric performances of as-grown samples and compared it with oxygen and hydrogen annealed ones. The structure of Ca12Al14O33 crystal was studied by powder x ray diffraction patterns, and the chemical processing efficiency was checked by optical transmittance measurements. The dielectric permittivity ɛ11 and piezoelectric coefficient d15 were found to be on the orders of 8–12 and 16–20 pC/N, respectively. This material exhibits good bulk shear wave coupling factor k14 about 0.34 and promising surface acoustic wave (SAW) velocities of 3500 m/s that render it suitable for SAW devices as a substrate. The piezoelectric response of crystals before and after annealing under H2 and O2 is maintained. The observed evolutions may be related to the conductivity of the material or the electrical transport properties, which are known to be sensitive to the oxygen and the hydrogen content.

The optical and magneto-optical properties of the {Tb3}[Sc1.95Lu0.05](Al3)O12 garnet (TSLAG) crystal are analyzed in detailed and compared with those of the reference compound Tb3Ga5O12 (TGG). TSLAG presents a very high transmittance, particularly higher than that of TGG in the visible region, and its Verdet constant is 20% larger at any wavelength. The figure of merit and extinction features point out the superior characteristics of TSLAG respect to TGG. A prototype, polarization independent optical isolator based on a TSLAG rotator is demonstrated at 1080 nm. Its performance confirms the high optical quality of this crystal, indicating its mature development for Faraday rotator applications.

The incorporation of Nd3+ in the ferroelectric fluoride BaMgF4 crystal is investigated for its potential application as self-frequency-converter solid state laser. Low temperature high-resolution optical spectroscopy shows that Nd3+ is located at two well distinguished sites referred as A and B. The whole set of energy levels in the excited F43/2, I411/2, and ground I49/2 states are identified for both Nd3+ sites and their crystallographic location in BaMgF4 lattice is discussed. The radiative lifetime of the F43/2 metastable laser level is obtained to be 1430 and 800 μs for site A and B, respectively, and the luminescence quantum efficiency of the F43/2 metastable state for the dominant A site is 87%. The possibility of annihilating the contribution of the B site in the optical spectrum is demonstrated by means of the incorporation Na+ into the crystal.

Electrical conductivity of β-Ga2O3 has been attributed so far to an oxygen deficiency, the donors presumably being oxygen vacancies. This letter shows, however, that the conductivity can be intentionally controlled over three orders of magnitude by Si doping. The related free-carrier concentration, which varies between 1016–1018cm−3, corresponds to a 25%–50% effective Si donors. Since Si is the main impurity present in Ga2O3 powders—in the order of the studied doping levels—we conclude that the electrical conductance of β-Ga2O3 can be attributed to Si impurities, and that the contribution of oxygen vacancies, if any, is not dominant.

Excitation and photoluminescence spectra of high purity and Si-doped β-Ga2O3 single crystals are investigated. Emission peaks in the UV and blue wavelength regions are observed. These are excited at two bands, which can be differentiated by polarized light. The features of the spectra are independent of excitation and emission wavelengths in the case of an undoped sample. On the contrary, after Si doping, the blue emission becomes strongly dependent. A model to interpret the characteristics of blue luminescence is proposed.

The temperature dependence of the electrical properties of β-Ga2O3 is analyzed from liquid helium to room temperature by Hall measurements. Below 100K, the carrier motion takes place within the impurity conduction band and it shows a power-law dependence. An electrostructural coupling is ascertained. Thermal activation in the conduction band is observed above 100K, with an activation energy Ea=7meV. Thermal conductivity is measured to 13Wm−1K−1. Further, it is shown that Ti is a good Ohmic electrode for n-type β-Ga2O3 substrates.

The epitaxial relationship between wurtzite GaN and monoclinic β-Ga2O3 is studied by transmission electron microscopy. GaN is grown on β-Ga2O3 by molecular beam epitaxy without any low-temperature buffer layer, obtaining c plane GaN on a plane β-Ga2O3. The effect of the surface nitridation, which is necessary for the epitaxial growth, is analyzed at the atomic level. The lattice mismatch has a minimum of 2.6% for the in-plane epitaxial relationship ⟨011⟩Ga2O3‖⟨101¯0⟩GaN.

The sidewise domain dynamic and wall strain behavior in the atomic force microscope (AFM) tip electric field has been investigated in ferroelectric BaMgF4 single crystal by piezoresponse force microscopy. Unusual 180° domain wall strain phenomenon and its dynamics in the domain decay process of BaMgF4 crystal were directly visualized by AFM. The dependence of the lateral domain size on the switching voltage pulse magnitude and duration was measured and discussed. It was shown that the defects in the crystal play an important role in such abnormal wall strain behavior, and the sidewise domain kinetics reveals an activation mechanism of the wall motion in the bulk BaMgF4 single crystal.

The ferroelectric properties of bulk BaMgF4 are determined by polarization hysteresis measurements. The spontaneous polarization Ps is found to be 6.6μC∕cm2, while the coercive field Ec varies between 4 and 24kV∕cm, depending exponentially on the frequency. Periodical poling of domains, with a 24μm period, is demonstrated and evidenced by a selective domain etching.

Epitaxial growth of β-Ga2O3 thin films by the rf-plasma-assisted molecular-beam epitaxy technique is demonstrated. Growth on (1 0 0) β-Ga2O3 substrates leads to very smooth epilayers, while (2 0 1¯) and (1 0 0) oriented β-Ga2O3 films are obtained on (0 0 1) sapphire and (1 0 0) MgO substrates, respectively. Internal transmittance, refractive index and direct bandgaps are determined.