Study On Polarization Regulation And Application Of GaN-based Ultraviolet LED Structure

Ultraviolet light-emitting diodes(UV-LEDs)have attracted much attention due to their wide-ranging applications in water purification,UV curing,environmental sensing,plant growth lighting,and phototherapy.However,the development of UV-LEDs is limited due to poor acceptor doping efficiency,low hole injection efficiency,electron leakage,severe current crowding,and quantum confinement stark effect(QCSE).Based on the above questions,the research contents of this paper mainly include: study on stress regulation of superlattice insertion layer,study on modulation doping of n-type layer,research on polarization regulation of p-type layer and research on polarization regulation in active region.Aiming at the QCSE problem,the superlattice insertion layer structure is proposed,and the effects of Al composition in the superlattice insertion layer on the band structure and carrier transport of UV-LEDs are studied by the Advanced Physical Models of Semiconductor Devices(APSYS).The simulation results show that the polarization effect of the multi-quantum well structure can be regulated by adjusting the Al component in the superlattice insertion layer.The improvement of Al composition in the superlattice insertion layer not only promotes electron injection but also blocks hole leakage,and the QCSE effect is alleviated.Samples with diffierent Al components are epitaxially grown by the Metal Organic Chemical Vapor Deposition(MOCVD)system.The experimental results show that the luminescence peaks in the active region and superlattice insertion layer show different states,which is related to the Al component in the superlattice insertion layer and the dislocation density in the samples.When the Al component in the superlattice insertion barrier layer is 0.05,the Wall-plug efficiency(WPE)of the device is about 8%.Compared with the relevant studies at home and abroad,this luminous intensity still has room for further improvement.Aiming at the current crowding problem in the lateral structure,we propose the modulation doping structure in the N3 heavily doped region.The use of modulation doping structure not only improves the crystal quality,but also makes the light distribution more uniform.The luminescence intensity and WPE of the samples with modulation doping structure are increased by 18.3 % and 17.8 %,respectively.The uniformly distributed lateral hole concentration in the quantum well in APSYS simulation analysis verifies that the use of the modulation doping structure in the N3 heavily doped region can indeed promote the uniform current spreading.Aiming at the low carrier injection efficiency problem,the two-dimensional hole gas(2DHG)and three-dimensional hole gas(3DHG)are theoretically investigated.The superlattice structure and Al graded Al Ga N structure can promote acceptor ionization and improve hole concentration.The Contact Hall test results suggest that the ionization rates are 7.5 % and 4 %,respectively.On this basis,we propose a method to improve the photoelectric performance of UV-LEDs by using double superlattice structure.Simulation analysis results show that the double superlattice structure mainly improves the carrier injection efficiency through three aspects:(1)increase the hole concentration by increasing the acceptor ionization rate;(2)hole injection efficiency is promoted by reducing the valence band barrier height of EBL;(3)electron leakage is prevented by raising the conduction barrier height of EBL.And samples with diffierent structures are epitaxially grown by MOCVD system.The experimental results show that the WPE of the samples with double superlattice structure is increased by 37.9 % at 120 m A.In addition,this paper investigates the influence of the barrier layer and well layer structure parameters in the multi-quantum well structure on the band structure,carrier distribution and internal quantum efficiency of Ga-polar and N-polar UV-LEDs,respectively.APSYS simulation analysis shows that the polarization effect can be regulated by adjusting the structural parameters of barrier layer and well layer in the active region,so as to improve the performance of the device.With the increase of Al component(well width)in the active region,the quantum well bending degree of the Ga-polar and N-polar samples increases and the band gap decreases.Although the quantum well bending degree and band gap of Ga-polar and N-polar samples have the same dependence on the Al composition and well width in the active region,compared with Ga polar samples,N polar samples have higher carrier injection rate and better blocking effect on electron leakage.So the IQE of the N-polar samples is higher and the Droop efficiency is lower.The experimental results show that the optical power of the devices are the optical when the Al component in the active region is 0.08(the well width is 2 nm).