Study On Epi-structure Simulation,device Fabrication And Optical-electrical-thermal Properties Of Micro-LED

Micro light-emitting-diodes(Micro-LEDs)have excellent characteristics such as low power consumption,high efficiency,small size and small capacitance,so Micro-LEDs have great application prospects in the fields of display,optical communication and implantable biomedicine.Compared with conventional LEDs,Micro LEDs have not only smaller size,but also different characteristics in luminous efficiency,carrier recombination lifetime and thermal effect,so further research is needed.This thesis systematically carried out the epitaxial layer structure simulation,device fabrication and optical-electrical-thermal characteristics measurement,which are aimed at scientific problems of Micro-LED,including efficiency improvement,luminescence mechanism and the influence of junction temperature on optoelectronic characteristics.The main research contents and results are as follows:1.We numerically simulated optical-electrical properties of blue Micro-LEDs with different epitaxial layer structures and systematically given optimization strategies for Micro-LEDs at low current density.We optimized the original MQW Micro-LED structure by selecting single quantum well(SQW),removing electron blocking layer(EBL),using appropriate N-doping concentration of n-side quantum barrier(QB),using optimized QB material and quantum well(QW)width.In theory,we achieved 92.3 % internal quantum efficiency(IQE)at a current density from 0.01 to 2 A/cm2 and a forward voltage of 2.72 V at 1 A/cm2.2.The flip-chip Micro-LEDs with built-in temperature sensor were fabricated,and the effects of temperature(120 K to 370 K),current density(0.01 A/cm2 to 1000 A/cm2)and size(19 to 63 ?m)on the Micro-LED were studied.We found that in the range of measured current,with the increase of junction temperature,the translation from blue shift to red shift of peak wavelength was observed,and the full width at half maxima(FWHM)showed complete or partial S-shaped changes.In the range of measured junction temperature,with the increase of current,the peak wavelength and the FWHM showed complete or partial S-shape changes.The results above can be explained by the conversion of two luminescence mechanisms(free and bound excitons),screening effect of the quantum-confined Stark effect(QCSE)and band filling effect.With the increase of temperature,the proportion of free exciton emission increased,while with the increase of current,the proportion of free exciton emission decreased.At the same current density and junction temperature,the peak wavelength undergone red shift with the increase of size.This can be explained by QCSE: the smaller the sample size,the more stress released,the weaker the QCSE,resulting in the blue shift of peak wavelength.3.Surface recombination had a great influence on the luminous efficiency of Micro-LED in this thesis.The smaller the size,the higher the proportion of surface recombination to total recombination,which leads to the decrease of peak IQE and the increase of current corresponding to peak IQE.Quantitative analysis showed that: based on the epi-wafer and fabrication in this thesis,small size LED(such as 8 ?m)has a peak IQE of 64 %.If one can introduce sidewall protection to suppress all surface recombination,peak IQE can be improved to greater than 85 %.