Study On The Related Ways Of Improving Carrier Injection In ?-Nitride-based Deep Ultraviolet Light Emitting Diodes

Al Ga N-based deep ultraviolet LEDs(DUV LEDs) are environmentally friendly,safe,efficient,and low power consumption.They have unique advantages in many aspects,including sterilization,water and air purification,food safety,medical treatment,UV communication,etc.In addition,ultraviolet light can destroy the bacterial gene chain,so the bacteria can not replicate and regenerate.Therefore,DUV LEDs have gained tremendous research interests.However,compared with the mature blue LEDs,DUV LEDs still have negative aspects limiting the performance.The polarization electric field caused by lattice mismatch leads to the quantum-confined Stark effect(QCSE)in the active region and thus reduce the electron-hole radiative recombination rate.Besides,non-radiative recombination of carriers due to defects in crystals and the Auger recombination,low p-doping efficiency in Al-rich Al Ga N layers,poor carrier injection efficiency and uneven carrier distribution in the active region also influence the quantum efficiency.Foutunately,the researchers are able solve the above problems by designing novel electron injection layer,hole injection layer,multiple quantum wells,and p-type electron blocking layer(p-EBL)for LED structures.The proposed structures of great innovation provide theoretical basis and important ideas for enhancing the luminescence for LEDs.This thesis mainly improves the optical properties of the III-nitride-based LEDs by increasing the carrier injection efficiency.The electron injection source layer and the hole injection source layer are designed and studied,and the influence on the carrier injection efficiency is further discussed.Due to the fact that electrons have high mobility and small effective mass,the electrons thus easily escape from the active region.Firstly,we propose manipulating the Si doping concentration in the electron injection source layer,and then we analyze the accompanying effect on the electric field.The electric field can affect the energy for the electrons before they enter the active region,and the electrons can be decelerated if the structure is properly designed.Therefore,the ability of multiple quantum wells(MQWs)to confine electrons is improved,which increases the electron concentration in the active region and reduces electron leakage.However,if the Si doping concentration is too high,this will hinder the hole injection efficiency.Therefore,we specifically optimize the electron doping concentration for DUV LEDs and the oretically explore the effects on carrier injection.In addition,the low hole injection efficiency is also the main reason for the poor device optical and electrical properties.Compared with electrons,holes have low mobility and large effective mass.We also take advantage of the electric field to increase the hole energy.Here,the electric field are modified by adjusting the Mg doping concentration of the hole injection source layer,which,if properly design,can accelerate the holes and thereby increase the hole concentration injected into the active region.At the same time,we insert p-Al Ga N layers with different Al compositions between the p-EBL and the p-Ga N layer.In addition,we also propose inserting p-Al_xGa_1-xN layers with different layer number and the different Mg doping concentration to further discuss the hole injection.In particular,the hole injection efficiency is increased by appropriately reducing the Mg doping concentration of high-order devices.Since the corresponding electric field increases the hole drift velocity,this then causes more holes to pass through the p-EBL and transport into the active region,eventually improving the device optical output power.