Study On Polarization Characteristics And Emission Efficiency Of ?-Nitride Ultraviolet Light-Emitting Diode

?-nitride ultraviolet light-emitting diodes(UV LED)have broad application prospects in the fields of sterilization,medical treatment,gas sensing,and polymer curing.At present,comparing with In Ga N-based LEDs,the external quantum efficiency(EQE)of Al Ga N-based UV LEDs is still very low,which hinders the progress of its commercial application.High Al-composition Al Ga N-based UV LEDs face the problems such as strong polarization electric field,poor hole injection efficiency,electron leakage,and low light extraction efficiency,thus the EQE usually was less than 10%.In particular,Al Ga N-based UV LEDs with the wavelength below 320 nm mainly emit TM(Transverse Magnetic)polarization,and the photon extraction efficiency is extremely low.Therefore,improving the polarization characteristics of UV LEDs is of great significance for the high-efficiency UV LED devices.This thesis uses kp theoretical calculation and APSYS numerical simulation methods to study the polarization characteristics of ?-nitride-based UV LEDs and the improvement of their efficiency.The main research contents are as follows:1.The degree of polarization of the Al_0.35Ga_0.65N-based UV LED is improved by increasing the compressive stress in the quantum wells.The effect of the composition of quantum barriers on the polarization characteristics and efficiency of UV LEDs is studied,and i PNi-type doped quantum barriers were adopted to improve the efficiency of UV LEDs.Firstly,the energy bands and transition matrix element squares of Al_0.35Ga_0.65N quantum well with different barrier composition are calculated by the kp method,and the TE polarization intensity of the valence bands HH1 and LH1 is significantly improved under the action of compressive stress.Then we used APSYS simulation to study the effect of different composition of quantum barriers on the performance of Al_0.35Ga_0.65N-based UV LED devices,it is found that although the quantum barriers with high Al-composition is beneficial to increase the degree of polarization of UV LEDs,the strong polarization electric field and increased barrier height of the quantum barriers will cause a decrease in the wave function overlap and difficulty in carrier transport.Therefore,we propose an i PNi-type quantum barrier structure.The simulation results show that the proposed structure can effectively reduce the polarization electric field strength,increase the wave function overlap of electrons and holes,and improve the hole injection efficiency.The output power of the UV LED is increased by 31.9%,and the efficiency droop is also reduced from 28.3%to 8.9%.2.The ultra-thin Ga N quantum wells are proposed to replace the Al Ga N-based quantum wells.The effect of composition of quantum barrier,barrier thickness and well width on the wavelength and efficiency of Ga N-based LEDs is studied,and an EBL-free structure is adopted to improve the hole injection efficiency.Firstly,the kp method is used to calculate the energy bands and transition matrix element squares of Ga N quantum wells with different well widths and barrier compositions.The quantum confinement effect increases the effective band gap of the Ga N well,and the TM polarization of the valence band CH1 increases.Then we used APSYS software to simulate the effect of barrier composition,barrier thickness and well width on the wavelength and performance of Ga N-based LEDs.It is found that the emission wavelength of quantum wells with well width less than 1.5 nm is not affected by the quantum confinement Stark effect(QCSE),and he main factor that determines the performance of the device is the carrier concentration.Finally,an EBL-free structure design of UV LEDs thin Ga N well and high Al-composition quantum barrier is proposed,which improves the hole injection efficiency.The LOP of the proposed UV LEDs is increased by 181.5%,and the efficiency droop is reduced from 69%to 10.2%.