ABSTRACT
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.
ABSTRACT
Nb, an expensive and refractory element with good wear resistance and biocompatibility, is gaining more attention as a new metallic biomaterial. However, the high price of the raw material, as well as the high manufacturing costs because of Nb's strong oxygen affinity and high melting point have limited the widespread use of Nb and its compounds. To overcome these disadvantages, porous Nb coatings of various thicknesses were fabricated on Ti substrate via selective laser melting (SLM), which is a 3D printing technique that uses computer-controlled high-power laser to melt the metal. The morphology and microstructure of the porous Nb coatings, which had pores ranging from 15 to 50 µm in size, were characterized with scanning electron microscopy (SEM). The average hardness of the coating, which was measured with the linear intercept method, was 392±37 HV. In vitro tests of the porous Nb coating which was monitored with SEM, immunofluorescence, and CCK-8 counts of cells, exhibited excellent cell morphology, attachment, and growth. The simulated body fluid test also proved the bioactivity of the Nb coating. Therefore, these new porous Nb coatings could potentially be used for enhanced early biological fixation to bone tissue. In addition, this study has shown that SLM technique could be used to fabricate coatings with individually tailored shapes and/or porosities from group IVB and VB biomedical metals and their alloys on stainless steel, Co-Cr, and other traditional biomedical materials without wasting raw materials.
