Study On The Effect Of Quantum Barrier Structure On The Efficiency Droop Of GaN-based LEDs

Gallium nitride(GaN)is a wide and direct bandgap semiconductor material,it has 3.4 eV wide bandgap at room temperature,GaN based materials' bandgap width can be adjusted easily,which is suitable for the preparation of optoelectronic devices,such as Light-emitting Diodes(LEDs),Lasers Diodes(LDs)and Photo Detectors(PDs).GaN-based LEDs have been widely used because of small size,long life,high brightnessand low energy loss.It is expected to replace traditional white-light lamps and fluorescent lamps as the main lighting source.The mainly requirements for LEDs in the lighting field are high-power and high efficiency,To obtain high power,the LED needs to work under high current injection.However,as the injection current increases,the efficiency droop of GaN-based LEDs is obviously.There is no clear explanation of efficiency droop.Several mechanisms have been proposed to explain this phenomenon,including the quantum Stark effect due to the polarization effect,Auger recombination,low hole injection efficiency,electron leakage,and so on.It is can be found all the mechanisms have direct or indirect connections with the LEDs quantum barrier structure.This thesis mainly studies the effect of quantum barrier structure on the efficiency droop of GaN-based LEDs.Firstly,analyze the various possible mechanisms for the LED efficiency droop,then design of GaN-based LEDs barrier structure.In order to reduces polarization effect and improve radiation recombination efficiency,Introducing aluminum(Al)into the traditional GaN barriers form AlGaN barriers,and designing various quantum barrier structures,improves the effective height of the quantum barrier layer in the LED light-emitting active region,and improve the ability to confine the carrier;Combining the electron blocking layer(EBL)of LEDs,optimize the last quantum barrier to reduce the electron leakage and improve the hole injection of efficiency of the LED;thus improving the efficiency droop of the device.The specific works is as follows1.Based on the traditional InGaN/GaN quantum well LED structure,a low Al composition Al0.05 Ga0.95N barrier was used to replace the traditional GaN barrier for research.The results show that:compared with the traditional GaN barrier,this barrier can effectively increase the height of the barrier,and can better confine the carriers,increasing the carrier concentration in the active region,and ultimately increasing the radiation recombination rate.2.Based on the low A1 composition quantum well barrier.In order to reduce the additional polarization electric field introduced by the AlGaN barrier,a triangular Al(GaN-AlGaN-GaN Triangle,GAGT)barrier structure is designed.The results show that the GAGT barrier increases the effective height of the barrier,and the barrier 's contact interface with the quantum well layer is still an InGaN-GaN interface,which can avoid the highly polarized AlGaN-InGaN interface formed by the AlGaN barrier.comparing with AlGaN barrier structure,the use of the GAGT barrier structure can further improve the photoelectric performance of GaN-based LEDs.3.AlGaN Electron Blocking Layer is usually introduced to confine electron leakage in the LED structure.However,strong strain polarization will be formed at the interface between the GaN barrier and the AlGaN electron blocking layer,and reducing the effective barrier height of the electron blocking layer.In order to optimize the structure of the electron blocking layer,this thesis uses the Al content gradient AlGaN special barrier to replace the last GaN barrier in the traditional LED active region,and remove the electron blocking layer in the traditional structure.The results show that this special structure LED can more effectively confine electron leakage.and the injection efficiency of holes has also been improved,the efficiency droop of LEDs has been finally improved.