A search for new phosphor materials that exhibit high light-emission, spectral purity, long-time stability and processability capture particular attention to modern solid-state lighting. Here, ...polymerizable silane pre-functionalized carbon dot (SiCD) fluids were dripped and co-polymerized or completely bulk polymerized to build color conversion and encapsulation coatings of commercially available GaN blue LEDs. Most parameters of SiCD-based white LEDs were similar to or even better than those of phosphor-based white LEDs, particularly the insensitivity to excitation wavelength and working current. Thus, SiCDs were superior to those phosphors in terms of broadband properties, high transparency (no light blocking and leaking), as well as arbitrary doping of its content as color conversion and encapsulation layers simultaneously, unique solubility, flexible chemical, optical and mechanical processability. Thus, designing new CD-based white LEDs, instead of inorganic rare earth phosphor-based LEDs, is possible for better performance solid state lighting devices.
Excitation power and temperature dependences of the photoluminescence (PL) spectra are studied in InGaN/GaN multiple quantum wells (MQWs). The excitation power dependences of the PL peak energy and ...linewidth indicate that the emission process of the MQWs is dominated first by the Coulomb screening effect and then by the localized states filling at low temperature, and that the nonradiative centers are thermally activated in low excitation range at room temperature. The anomalous temperature dependences of the peak energy and linewidth are well explained by the localized carrier hopping and thermalization process, and by the exponentially increased density of states with energy in the band tail. Moreover, it is also found that internal quantum efficiency is related to the mechanism conversion from nonradiative to radiative mechanism, and up to the carriers escaping from localized states.
This study aimed to investigate temperature dependencies at different injection currents (ICs) of the electroluminescence (EL) spectra from a green InGaN/GaN light-emitting diode (LED) based on ...multiple quantum wells (MQWs) grown on a Si substrate in a wide range of ICs (0.001-350 mA) and temperatures (6-350 K). The results show that the temperature-changing characteristic of the EL peak energy gradually evolves from an approximately V-shaped temperature dependence into a wave-shaped (three-step blueshift) dependence with increasing IC. Finally, it emerges as an approximately inverted V-shaped temperature dependence. The behavior reflects the fact that the emission related to InGaN is significantly influenced by the changing recombination dynamics of carriers with rising temperature or IC. This is attributed to the presence in the MQW active region of a stronger carrier localization effect across three zones with different average In contents. Moreover, with the decline of the temperature at lower ICs, the temperature behavior of the external quantum efficiency (EQE) value is dominated by the deactivated non-radiative centers. This phenomenon occurs not only in the higher temperature range but also at lower temperatures due to more In-content-induced structural defects, which are confirmed by measurements of the integrated EL intensity as well as the EQE dependence on IC.
Silicon-diaphragm-based fiber-optic Fabry-Perot sensors with different intracavity pressures were fabricated by anodic bonding and microelectromechanical techniques. The thermal stress and thermal ...expansion of the Fabry-Perot (FP) sensor caused by high-temperature bonding and temperature change were simulated by finite-element analysis. The calculated thermal stress is largest in the center and edge regions of the resonance cavity, reaching from 2 to 6 MPa. The reflection spectra and temperature sensitivity of the sensors were simulated by using a two-dimensional wave-optic model in Comsol. Theoretical calculations were also made for the FP cavity without considering silicon-diaphragm deformation and thermal stress. Four sensors with intracavity pressures of 0.01, 0.03, 0.04, and 0.05 MPa were tested at low temperatures, showing a high degree of consistency with the simulation results rather than theoretical calculation, especially for high intracavity pressure. This method is expected to aid the analysis of thermal stress generated during the bonding process and to facilitate better design and control of the temperature sensitivity of the sensor.
Compared with the first and second generation semiconductor materials, the third generation semiconductor materials exhibit higher breakdown field strength, higher saturated electron drift ...velocity,outstanding thermal conductivity, and wider band gap, suitable for manufacturing of electronic devices with high frequency, high power, radiation resistance, corrosion resistant properties, optoelectronic devices and light emitting devices. As one of the representatives of the third generation of semiconductor materials, gallium nitride（GaN） is an ideal substrate material for preparing blue-green laser, radio frequency（RF） microwave and power electronic devices. It has broad application prospects in laser display, 5G communication, phased array radar, aerospace, etc.Hydride vapor phase epitaxy（HVPE） method is the most promising method for growth of GaN crystals due to its simple growth equipment, mild growth conditions and fast growth rate. Due to the widely used quartz reactors,unintentionally doped GaN obtained b
The reduction of electron mobility in AlGaN/GaN heterostructures follows the common power law, but with an unexpectedly high power coefficient. Following the experimental verification of the unusual ...power-coefficient value by a different measurement method, this brief presents an analysis that identifies the temperature dependence of the effective electron mass as the responsible physical mechanism for this effect. Based on this result, the measured values of electron mobility are used to calculate the effective mass of the electrons in AlGaN/GaN heterostructures over a wide temperature range, from 25 °C to 300 °C.
SiC semiconductor is the focus of recent international research. It is also an important raw material for China to achieve carbon emission peak and carbon neutrality. After nearly 20 years of ...research and development, we focus on the three types SiC crystals, n-type, p-type and semi-insulating, indicating the development of Shandong University for crystal growth. And defects control, electrical property, atomic polishing, and corresponding device authentication all obtain great progress. Total dislocation density of 6-inch n-type substrates decreases to 2307 cm
, where BPD (Basal Plane Dislocation) lowers to 333 cm
and TSD (Threading Screw Dislocation) 19 cm
. The full width at half maximum (FWHM) (0004) rocking curves is only 14.4 arcsec. The resistivity reaches more than 1E + 12 Ω·cm for semi-insulating SiC and lower than 20 mΩ·cm for n-type SiC. The impurity concentrations in 6-inch high-purity semi-insulating (HPSI) SiC crystals reach extreme low levels. The devices made of various substrate materials have good performance.
The excellent optoelectronic properties of graphene give it great potential for applications in optical detection. Among the graphenes obtained through many synthetic methods, epitaxial graphene ...obtained by thermal decomposition on silicon carbide has remarkable advantages for preparing photodetectors. In this research, epitaxial graphene has been successfully prepared on a silicon surface (0001) of semi-insulating 4H-SiC substrate with a size of 10 mm × 10 mm and epitaxial graphene has been converted to quasi-free-standing graphene by hydrogen passivation. Two metal-graphene-metal photodetectors were fabricated using the two types of graphenes above and the photo-absorption properties of detectors have been investigated under 650-nm laser illumination with different illumination powers. From a comparison of the performances between the two detectors, it was found that a photodetector fabricated with quasi-free-standing graphene shows enhanced performance under a light power of 0.018 mW. Responsivity and external quantum efficiency reach maxima of 5.11 A/W and 9.74%, respectively. This dramatic improvement is mainly due to the disappearance of the buffer layer in epitaxial graphene, providing a new method to achieve optimization of graphene-based opto-electrical devices.
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