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Spatial charge relaxation in glasses poled in the air and argon atmospheres
摘要： Thermal poling of a multicomponent silicate glass was performed in air and in argon atmospheres at various voltages, and the temperature dependences of the depolarization currents (TSDC) in the poled glasses were studied. In addition, the concentration profiles of univalent and bivalent cations in subanodic regions of the poled glasses were measured with EDS and SIMS techniques. The difference in the displacements of bivalent ions at poling of the glasses in closed and open anode configurations allowed us to identify “frozen” spatial charge relaxation peaks observed in the TSDC measurements and to relate these peaks to hydrogen and bivalent metal ions relaxation.
关键词： spatial charge relaxation,silicate glass,thermal poling,depolarization currents,hydrogen and bivalent metal ions relaxation
更新于2025-09-12 10:27:22
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Mechanism of improved luminescence intensity of Ultraviolet Light Emitting Diodes (UV-LEDs) under thermal and chemical treatments
摘要： In this work, the influences of thermal annealing and chemical passivation on the optical and electrical properties of ultraviolet light-emitting-diode (UV-LED) were investigated. The electroluminescence (EL) intensities of the LEDs under KOH treatment and thermal annealing increased by 48% and 81%, respectively compared to as-fabricated LED under current level of 10 mA. Cathodoluminescence (CL) mapping of UV-LEDs confirmed no variation of the density of the non-radiative recombination centers after surface treatments, and no obvious change in surface morphology was identified due to lacking of energy for surface atom migration. However, Raman spectroscopy indicates a relaxation of compressive strains inside the thin film after both thermal and chemical treatments, and conductive atomic force microscopy (c-AFM) also illustrated reduced leakage current after KOH passivation, which are responsible for the improved luminescence properties of UV-LEDs.
关键词： surface treatment,UV-LED,electroluminescence,strain relaxation
更新于2025-09-12 10:27:22
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Strain-Related Degradation of GaN-Based Blue Laser Diodes
摘要： Degradation of GaN-based laser diodes (LDs) is studied using Electroluminescence (EL) and Transmission Electron Microscopy (TEM). The slope efficiency decrease is observed in addition to threshold current increase. Further studies on the optical loss and microstructures of the LDs indicate that the reduction of the slope efficiency is attributed to the increase of optical loss (from 14.2 cm-1 to 24.2 cm-1) and decrease of injection current efficiency induced by the defect generation around the waveguide and cladding layers. Injection current induced blue-shift of the spontaneous EL peak reduced after > 3000 hrs operation, which is ascribed to the compensation of Quantum-Confined Stark Effect (QCSE) caused by partial strain relaxation near the active region.
关键词： Spectroscopy,Degradation,Strain relaxation,Semiconductor lasers,Linewidth
更新于2025-09-12 10:27:22
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Plasma formation and relaxation dynamics in fused silica driven by femtosecond short-wavelength infrared laser pulses
摘要： Laser-induced plasma formation and subsequent relaxation in dielectric solids is the precursor to structural modi?cations serving as the basis for direct laser writing of functional optical micro- and nanostructures. Based on an experimental arrangement combining a time-resolved transmission measurement with a cross-phase modulation measurement, we isolate the plasma formation and relaxation dynamics in the bulk of amorphous fused silica excited by femtosecond short-wavelength infrared (k ? 2100 nm) laser pulses. Whereas the relaxation time of the generated subcritical electron-hole plasma was so far assumed to be constant, our ?ndings indicate an intensity-dependent relaxation time. We attribute this intensity dependence to vibrational activation of the medium, leading to detrapping of trapped carriers and a reduced trapping probability.
关键词： plasma formation,femtosecond laser pulses,relaxation dynamics,fused silica,short-wavelength infrared
更新于2025-09-12 10:27:22
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Fabrication of Less Bowed Light-Emitting Diodes on Sapphire Substrates with a SiO2 Thin Film on Their Back Sides
摘要： In this study, less bowed light-emitting diodes (LEDs) were fabricated by preparing a LED structure on a sapphire substrate with a SiO2 thin ?lm on its back side. The SiO2 thin ?lm with a low thermal expansion coe?cient reduced the bow of the wafer generated by the thermal expansion coe?cient di?erence. As the thickness of SiO2 was increased from 1 μm to 4 μm, the compressive stress in the GaN ?lm was reduced from 16% to 62% with respect to that without SiO2 thin ?lm. The stress reduction in multiple quantum wells also enhanced the internal quantum e?ciency of the LED by reducing the piezoelectric ?eld.
关键词： Stress relaxation,Internal quantum e?ciency,Light-emitting diodes
更新于2025-09-12 10:27:22
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Pulse shaping by a frequency filtering of a sawtooth phase-modulated cw laser
摘要： The spectrum of a cw field the phase of which experiences a periodic sawtooth modulation is analyzed. Two types of the sawtooth phase modulation are considered. One is created by combining many harmonics of the fundamental frequency. The second is produced by an electro-optic modulator fed by the relaxation oscillator, which generates a voltage slowly rising during charging of the energy storage device and dropping fast due to discharge by a short circuit. It is proposed to filter out the main spectral component of the sawtooth phase-modulated field. This filtering produces short pulses from the phase-modulated cw field. The duty cycle of this train is equal to the modulation period, while duration of the pulses depends on the rate of the phase drop. In the case of harmonics, this duration is 4N + 2 shorter than the period of the fundamental frequency, where N is the number of the harmonics. In the case of the charge and discharge, duration of the pulses is close to TD/2, where TD is a drop time of the phase in the discharge period. Depending on the modulation frequency, the proposed method is capable to produce pulses with duration ranging from nanoseconds to a fraction of a picosecond.
关键词： relaxation oscillator,electro-optic modulator,frequency filtering,sawtooth phase modulation,pulse shaping
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Study of Tm-Doped Aluminosilicate Films for Integration of Lasers on a SOI Silicon Photonics Platform
摘要： Thulium-doped glass has recently been highlighted as a potential candidate for amplifiers in a new telecommunications window, due to its potential for strong gain across a broad bandwidth in the 2-micron regime. However, the use of such technology in a silicon or planar platform has received much less attention. Lack of on-chip lasers is an obstacle to progress in silicon photonics with much research focused on mounting processed III-V lasers, bonding gain material, or the deposition of gain material onto SOI wafers. Here we report the preparation and study of Tm-doped aluminosilicate glass, which has been demonstrated as an efficient laser/amplifier in fibre-technology covering a 1.7-2.1 μm window. To achieve efficient operation the Tm3+ doping concentration is typically optimised for enhancing cross relaxation energy exchange between the 3H4 and 3F4 energy levels allowing an efficient “two-for-one” pumping approach. Fluorescent emission and gain can then be achieved by pumping with readily available ~795 nm sources diode-lasers. As such we have started preliminary investigations of higher concentrations to attempt to obtain enhanced gain per unit length devices.
关键词： silicon photonics,2-micron regime,Tm-doped aluminosilicate,on-chip lasers,cross relaxation energy exchange
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Intravalley Spin-Flip Relaxation Dynamics in Single-Layer WS <sub/>2</sub>
摘要： Two-dimensional Transition Metal Dichalcogenides (TMDs) have been widely studied because of the peculiar electronic band structure and the strong excitonic effects. In these materials the large spin-orbit coupling lifts the spin degeneracy of the valence (VB) and the conduction band (CB) giving rise to the A and B interband excitonic transitions. In monolayer WS2, the spins of electrons in the lowest CB and in the highest VB at K/K’ point of the Brillouin zone are antiparallel resulting in an intravalley dark exciton state at a lower energy than the bright exciton. Here we use two-colour helicity-resolved pump-probe spectroscopy to directly resolve the intravalley spin-?ip process of the photoexcited electrons in the CB of single-layer WS2. We ?nd that at T=77 K this process occurs on a sub-ps time scale and it is signi?cantly dependent on the temperature, strongly pointing to a phonon assisted relaxation process. Our results shed light on the intravalley spin relaxation process in single-layer WS2, determining the formation of the intravalley dark exciton, which we measure to occur on a sub-ps timescale. The study of dark excitons formation dynamics is important for designing TMD-based electronic/photonic devices.
关键词： WS2,spin-?ip relaxation,exciton,pump-probe spectroscopy,Transition Metal Dichalcogenides
更新于2025-09-11 14:15:04
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Postannealed Structural Relaxation and Phase Evolution of Quaternary Alloy BeMgZnO
摘要： The thermal stability of quaternary alloy BeMgZnO was investigated in this study. When a Be0.09Mg0.19Zn0.72O alloy film was annealed, structural relaxation and reconstruction of the film layers were found at 600, 700, and 800 °C. Be atoms were found to gradually diffuse out from the host lattice, and Mg atoms were still maintained. As a result, a mixed-phase alloy containing BeO and MgxZn1?xO was continuously generated. Correspondingly, the bandgap of Be0.09Mg0.19Zn0.72O reduced because of the diffusion of Be atoms. Hence, the thermodynamic solubility of BeO in ZnO and MgO was demonstrated to be relatively low. Additionally, the aging effect caused by a higher annealing temperature is more effective than that caused by a lower annealing temperature for a longer time. Due to the improvement of crystal quality, an MSM interdigital structure photodetector based on the 800 °C annealed sample was fabricated and revealed a strong response to the UV light. Our finding provides a new understanding of the ultrawide bandgap quaternary alloy BeMgZnO and contributes to a significant step toward its practical applications.
关键词： bandgap,photodetector,Be diffusion,BeMgZnO,thermal annealing,structural relaxation
更新于2025-09-11 14:15:04
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Dynamical processes related to viscous flow in a supercooled arsenic selenide glass-forming liquid: Results from high-temperature 77Se NMR spectroscopy
摘要： Dynamical processes in supercooled AsSe9 liquid are studied using 1D and 2D 77Se NMR spectroscopic techniques. The results demonstrate the coexistence of two distinct dynamical processes: one is a slow process related to the chemical exchange between the various Se environments by bond scission/renewal and the other is the fast Se chain segmental motion, which leads to the rapid averaging of the chemical shift anisotropy. The timescales of these two processes become increasingly similar as the glass transition is approached from above. The slow process is found to be closely coupled to viscosity over the entire temperature range of investigation and its activation energy is consistent with the Se-Se/As bond energies. On the other hand, the activation energy of the fast process is significantly higher, which may be indicative of its cooperative nature. This process becomes coupled to viscosity only in the immediate vicinity of the glass transition.
关键词： Supercooled liquid,Relaxation,Chalcogenide,Viscous flow,Glass transition,NMR spectroscopy
更新于2025-09-11 14:15:04