Design And Fabrication Of Embedded-contact Vertical Structure LED Chips

The core qualities of LED chips are high-power and low-cost,which is essential for the future solid-state lighting technology.However,there are still a series of unsolved technical difficulties such as current crowding,efficiency droop effect,and thermal effect,which have been limiting the further improvement of the performance of LEDs for a long time.To realize the further development of LED,it is necessary to systematically solved these technical difficulties on the research of high-power LED.As a new LED chip structure,the embedded electrode structure has great potential in the development direction of large-size and high-power LED chips.Taking the chip structure design as the starting point,we explored the simulation and process design of EC-VTF LED chip in this article,respectively.The main achievements are listed as follows:1.The physical model of EC-VTF LED chip with inserting GaN/AlGaN superlattice structures was simulated by using APSYS simulation software.The simulation results showed that the effect of SLs on current spreading became stronger with the decrease of the doping concentration in AlGaN and the increasing of Al.But the operating voltage also increased due to the increasing barrier height.In combination with actual experiments,the GaN/Al0.12Ga0.88N superlattice layers with a doping concentration of 2×1018 cm-3 was selected and inserted into the existing LED epitaxial structure and made into a chip.The data showed that the brightness of the chip increased by more than 3%,while the voltage only lift by 0.02 V,and the actual photoelectric efficiency upgraded by 1.4%.2.The ohmic contact characteristics and thermal stability of Cr/Al/Ni/Au and Ti/Al/Ni/Au were compared.The results displayed that the ohmic contact with ?c=8.82×10-5 ?·cm-2 could be formed after Cr/Al/Ni/Au were deposited.And it could still maintain good ohmic contact performance when annealed at 500 ?.It proved that Cr/Al/Ni/Au were more suitable for the embedded-contact vertical thin-film LED chips.3.The effects of etching gas formulation conditions and surface cleaning treatment processes on the Ga face GaN surface band bending were analyzed.The results showed that the surface band bending of n-GaN was reduced from 1.4 eV to 0.54 eV,and the contact resistivity was greatly reduced to 4.41×10-5 ?·cm-2,When using Cl2&N2 mixed gas for ICP etching in electrode hole preparation and SPM solution for surface cleaning treatment before metal deposition.The data showed that the optimized process reduces the chip operating voltage over 0.1 V and greatly narrowed the distribution range.