GaN-based Green Resonant Cavity Light-Emitting Diodes

GaN-based light-emitting diode(LED)has the characteristics of low driving voltage,good temperature stabilities,high efficiency,and advantages of environment protection.Green light emitter has been deeply studied and widely used in the fields of lighting,display,detection,measuring,and communication.The normal LED chip has low extraction efficiency due to the influence of total reflection.Resonant cavity light-emitting diodes(RCLEDs)have the potential to achieve high extraction efficiency,high spectral purity,high temperature stability,and high modulation bandwidth.In addtion,it is of great significance to improve the performance of green LEDs.The preparation of green light emitters requires the use of high-indium-component In GaN quantum wells.However,high-indium components cause lattice mismatches and large strains,which in turn lead to defects and polarization problems,therefore ultimately deteriorate the optical efficiency.In this thesis,the numerical simulation is used to study the high output power green RCLEDs.The structure parameters of the resonant cavity,including the length of the resonant cavity and the number of the distributed Bragg reflector pairs,are optimized.The performance of the green RCLED after structural optimization is given.Three trapezoidal gradient quantum wells have been introduced to improve the quantum efficiency of the device and the inherent mechanism was explored.The effects of chip size and ambient temperatures on the performance of RCLEDs are investigated.The influence of polarization charge density,Auger recombination coefficient and Shockley-Read-Hall(SRH)recombination lifetime on the performance of nitrogen-oriented asymmetric trapezoidal quantum wells(NOAT-QWs)and conventional symmetric square QWs(SS-QWs)are also analyzed.The results show that as the thickness of the resonant cavity increases,the output power oscillates.When Light Output Power(LOP)reaches the maximum value,the thicknesses of n-GaN and p-GaN are 1710 and 200 nm,respectively.The difference between the maximum value and the minimum value is 1.45 times.As the Distributed Bragger Reflector(DBR)number increases,the optical output power and half-height full-width of the RCLEDs decrease,so it is necessary to select the DBR pairs according to the application scenario.Comparing to the RCLED with SS-QWs,the quantum efficiency of the RCLED with gradient quantum well is increased by 30% and the light output power is increased by a maximum of 1.53 times.At the same current density,as the size increases,the light-emitting area,the total amount of radiation,and the light output power increase.Although the small-size chip has low optical power,the internal heat source density is also low,therefore the internal quantum efficiency is high and the temperature stability of radiation spectrum from quantum wells is good.High temperature can easily cause leakage of electrons,leading to reduced chip performance.In a polarization field,RCLEDs with NOAT-QWs always have higher efficiency than SS-QWs.For the case of non-polarization,SS-QWs improves the uniformity of hole concentration,so leads to higher efficiency than the NOAT-QWs.For the RCLEDs with various Auger and SRH recombination coefficients,a small-size chip always has higher efficiency than a large-size chip and a NOAT-QWs RCLED always has better performance than a SS-QWs RCLED,that is,no matter whether the non-radiative recombination coefficient increases or decreases,NOAT-QWs can show better performance.