Basic Research On Fluorescent SiC For Semiconductor Lighting

The 21 st century is the era of LEDs.The conventional white light LED is prepared by coating a yellow phosphor with a nitride-based blue LED.As mentioned in the 2014 Nobel Prize in Physics,blue LEDs are inventions that bring huge benefits to all human beings.Over time,it has been found there are still some problems with nitride-based blue LED such as:a low yield of the color quality,a low total flux,a low color rendering index(CRI),high-cost and a short lifetime.These problems are still serious obstacles for the expansion of white LED to enter into the general lighting applications.In order to solve these problems,a series of new technologies have emerged,such as OLED and Micro LEDAs a wide indirect band gap material,SiC is only used as a substrate material in the LED field.The donor-acceptor co-doped fluorescent SiC(f-SiC)is a new type of substrate for preparing white LED,which has the advantages of high efficiency,high color rendering index,longer lifetime,and good lattice matching.The effect of optimal doping concentration and crystal quality on f-SiC's photoluminescence intensity has been discussed in detail,but the effects of temperature,excitation power,and defects on their photoluminescence need to be further discussed.In this study,the effect of carrier concentration on electrical and luminescent properties and the effects of defects and temperature on photoluminescence were investigatedN-B co-doped SiC,as an excellent candidate for white LEDs,were prepared by physical vapor transport growth method.The carrier concentration information of samples A1-A4 was characterized by SIMS,resistivity,LOPC mode of Raman spectrum and absorption spectrum.As the B doping concentration increases,the free carrier concentration decreases and the resistivity increases.According to Raman mapping results and XRD test results,the polytype and the crystal quality are not affected by high concentrations of donor and acceptor doping.In order to explore the photoluminescence properties of the sample,the PL spectra and the excitation spectra were measured.The band-to-band excitation mechanism of donor and acceptor pairs(DAPs)luminescence and threshold energy in f-SiC have been clarified.When the excitation power increased from 2 mW to 44 mW,the luminescence intensity can be well fitted by the power dependence I=aPY.At same time,the luminescence peaks of high doping concentration samples shift to the high energy with high excitation power.The shifts and the underlying mechanism have been discussed.The effect of different defects on the photoluminescence of f-SiC was discussed by PL-mappingThrough the temperature dependent PL spectra in the temperature range of 40 K-300 K,three luminous mechanisms of e-A,DAP and Band3 are discussed.At different temperatures,changes in the carrier recombination rate and non-radiative recombination rate affect the luminous intensity.The shallow B level will trap holes,which affects the change in DAP emission intensity with temperature,but this effect is small in sample with high B doping concentration.The intensity ratios of e-A and DAP at different temperatures are related to the B-doping concentration.The intensity of e-A emission is more sensitive to B doping concentration than the DAP intensity.The fluorescence lifetime of N-B co-doped fluorescent SiC can reach the order of milliseconds.And as the test temperature increases,the possibility of non-radiative recombination increases,resulting in a decrease in lifetime.