First-principles Calculations And Design Of Electron Blocking Layer Of GaN-based Light Emitting Diodes

Due to the wide band gap of AlGaN material,which has been extensively used as an electron blocking layer?EBL?of GaN-based LED.The meaning of its existence can suppress the electron leakage from the InGaN/GaN multiple quantum wells,and increase the recombination efficiency of the electron and hole,thus improving the quantum efficiency of LED.Prof.Fengyi Jiang of Nanchang University has been found that a suitable AlGaN EBL structure with Al fraction can effectively suppress the electron overflow,as well as promote the hole injection,to enhance the quantum efficiency in GaN-based LED.Insight into the physical mechanism of the interfacial characteristic of AlGaN EBL contacting on InGaN/GaN MQWs,and the physical mechanism of AlGaN EBLsupressing electron leakage from the active layer,which have important scientific value a practical significance to reduce the“efficiency droop”and improve the high performance of GaN-based LED.In this paper,based on the density function theory,first-principles calculations were performed to study the physical mechanism of AlGaN EBL suppressing the electron leakage from active layer.To sum up,there are mainly:Various thicknesses of AlN/GaN?0001?and Al_xGa_1-xN/GaN?0001??0<x?1?superlattices with different Al compositions are established,and the macroscopic averaging method is carried out to study the band offsets and polarization electric fields of these interfaces.Thiknesses of AlN/GaN?0001?SLs can adjust the band offsets and polarization electric fields,which lays the foundation for invesgation the interfacial property of Al_xGa_1-xN/GaN?0001?SLs with different Al compositions.VBO?x??-0.3378x²+0.6596x-0.0119?eV?,and CBO?x??0.4006x²+0.9401x-0.0187?eV?of Al_xGa_1-xN/GaN?0001?SLs are obtained,respectively;Meanwhile,the polarization electric fields become stronger with increasing Al compositions.These results demonstrate that selecting the AlGaN EBL structure with a suitable Al concentration can suppress the electron leakage from active region,as well as promote the injection of hole from the p-GaN,which are in agreement with the experiment reported by Jiang et al.that the physical mechanism of AlGaN EBL with a suitable Al fraction confines the electron overflow.First-principles calculations are performed to analyze the electronic structure of Al_xGa_1-xN/GaN?0001?SLs with different Al compositions.More charges accumulation,stronger polarization electric filed,increasing band offset and the band bending are found at the interface with increasing Al concentrations.Based on the physical mechanism of AlGaN EBL confining the electron leakage,the degree of electron leakage in InGaN/GaN MQWs with different In-content are further investigated.It is found that the band offsets and polarization electric fields of In_yGa_1-yN/GaN?0001?interfaces can be modulated by In-content,causing different degrees of electron leakage.We propose a"synergistic effect":there exists a synergistic relationship between the In-content in the InGaN/GaN MQWs and the Al composition in AlGaN EBL of GaN-based LED.The proposed“synergistic effect”of Al concentration in EBL and In-content in MQWs provides a method to better improve the quantum efficiency of GaN-based LED.