| AlGaN-based DUV-LEDs have drawn rather considerable interest in recent years because of a variety of applications in many areas,such as water and air purification,sterilization and biomedicine,optical storage,solid-state lighting,and full-color display.However,external quantum efficiency is still not high for AlGaN-based DUV-LEDs with emission wavelength under 300nm,and reasons include that high density dislocation in AlGaN templates grown on sapphire substrate,high ionization energy of Mg acceptor,low injection efficiency for hole and feeble confinement for carriers.Low hole injection efficiency and strong electron leakage are among the most important causes resulting in poor internal quantum efficiency.In order to enhance the confinement of carriers in the active region and the luminous intensity,several research groups have designed different device structures to improve performance of DUV-LEDs.In this study,we focus on the p-type doping layer of AlGaN-based DUV LEDs.Based on the original experimental data and simulation work of the research group,we put forward the reference AlGaN DUV-LED structure.After a sequence of investigation and analysis,we designed special structures which replace the conventional p-type AlGaN layer with a superlattice p-type doping layer above the EBL for improving the performance of LEDs.The extraordinary design of DUV-LEDs with varied barrier PSL and conventional structure has been investigated numerically by Advance Physical Model of Semiconductor Devices(APSYS),and the performance of the new structure has enhanced significantly.To explain the phenomenon,we simulated carrier concentration distributions and energy band diagrams in order to make the physical mechanism clear,and verified by experiments.The main contents are as follows:1)First,the basic properties and luminescence mechanism of AlGaN-based DUV-LEDs are briefly introduced.Then,the market prospects,problems and solutions of DUV-LEDs are discussed.Then we introduced the simulation method of AlGaN-based DUV-LED,such as the physical model and basic equations of semiconductor devices..2)The photoelectric properties and physical mechanism of AlGaN-based DUV-LEDs with the superlattice p-type doping layer(PSL)are studied numerically and compared with the Al-composition(50%)conventional p-type layer AlGaN-based DUV-LEDs.We have constructed four different structures of LEDs by APSYS software.Structures A,B,and C are novel superlattice p-type doping structures,the Al composition in the well of the superlattice is 0.4.The Al composition in the barrier layer is different,corresponding to structures A,B,and C are 0.5,0.55,and 0.6,respectively.Structure D is a conventional p-type doping structure.Through comparing the internal quantum efficiency(IQE),light output power,electroluminescence intensity(EL),electrostatic field,radiative recombination rate,distributions of carrier concentration and the energy band diagrams,the property of AlGaN-based DUV-LED with the PSL has enhanced significantly.Moreover,the 55%-Al-composition of superlattice barrier p-type doping layer greatly reduces the effective potential height for holes in valence band,which is beneficial for hole injection from PSL.The new structure improves the properties of DUV-LED and shows remarkable output performance.3)The epitaxial growth and characterization of PSL AlGaN-based DUV-LEDs are introduced.In order to verify them experimentally,we have used the metal oxide chemical vapor deposition(MOCVD)method to grow theoretically simulated new P-type superlattice structures B and the conventional structure D.We characterized two samples by experiment,containing tests for PL and CL characteristics.The results show that performance of the new structure has enhanced significantly,that are consistent with the simulation calculations of the APSYS software.Therefore,the adoption of superlattice p-type doping layer in the structure to improve the overall performance AlGaN-based DUV LEDs is reasonable and the new structure will have good application prospect. |
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