Optimization Of P-type Layer Structure Of GaN-based UV LED

Since the successful preparation of Ga N-based materials,LEDs made of III-V compound semiconductors and their alloys have quickly become a research focus.LED has been widely used in solid-state lighting,decoration,sterilization and other fields due to its long life,energy saving,high stability and other characteristics,It has also been used to promote development.In recent years,LED visible light band has made great progress in improving light output efficiency and reducing cost.Compared with visible light technology,the development of LEDs in the ultraviolet band still has many limitations,including: lateral device current congestion,poor device heat dissipation,low light extraction efficie ncy,and difficulty in obtaining high-conductivity p-type materials.For the ultraviolet light source,most of the current mercury lamps are on the market.Mercury lamps are not only unfriendly to the environment,but also have a problem of wide emission spectrum.Ga N-based UV LEDs are environmentally friendly and have a narrow emission band,making them the only alternative to mercury lamps.At present,the improvement of LED devices mainly includes improving the growth process(such as changing the growth temperature of certain layer structures),changing the doping method(such as co-doping,modulation doping,etc.)and changing the layer structure.This article mainly analyzes and studies what kind of performance changes the layer structure changes can bring to the device from the perspective of changing the p-type layer structure,we designs and grows three sets of samples with different p-type layer structures,and performs die processing on the epitaxial wafer to obtain LED chips.Atomic force microscopy(AFM),photoluminescence(PL),electroluminescence(EL)and chip optoelectronic performance analysis were performed on the obtained experimental epitaxial wafers,and the effects of structural changes and the mechanism of these effects were analyzed.The main contents of this article are as follows:1.We deeply analyze the effect of p-type layer insertion of Al Ga N/Ga N superlattice and p-type Al Ga N of graded Al composition on p-type layer.The superlattice structure bends the energy band of the superlattice interface,reduces the activation energy of the acceptor,and generates a high-density surface charge at the interface,thereby achieving the purpose of increasing the hole concentration of the superlattice material.The composition of the short-period superlattice Al is controlled so that the lattice constant exhibited by its structure matches the lattice constant of the superstructure to achieve the purpose of stress modulation.Based on this,the mechanism that affects the device performance by using Al Ga N with a progressive Al composition structure as the p-type layer is analyzed.The high-density surface charge generated at the super lattice interface,the 2D surface charge will become 3D if the structure is a Al gradually changing structure,thereby achieving the purpose of increasing the carrier concentration.2.Design three groups of samples,the p-type layers of which are: ordinary p-Ga N,inserted short-period Al Ga N / Ga N superlattice,and Al-graded Al Ga N.The chip was analyzed for crystal quality and photoelectric performance.The results show that the epitaxial wafers with the superlattice structure have the best growth quality,the structure with gradually changing composition takes second place,and the samples with ordinary structure have the worst.The epitaxial wafer was analyzed by PL,and it was found that the emission wavelengths of the three samples were all around 395 nm,but the luminous intensity increased successively.The optical output power of the device was tested.At 350 m A,the output power values were 502.3m W,600.3m W,and 635.8m W.The device was tested for operating voltage and found that at 350 m A,the working voltages of the three samples were 3.362 V,3.340 V,and 3.333 V.Finally,the external quantum efficiency of the device was analyzed.The external quantum efficiency of the three samples also increased in sequence.At 350 m A,the external quantum efficiency of the Al-gradient structure was increased by 13.5% and 7.8% compared to the other two structures,respectively.A simple analysis of the leakage performance of the sample was conducted,and it was found that the structure with gradual Al composition can reduce the leakage to a certain extent.