Study On Manufacturing Technology Of Highly Efficient Light-Emitting Diodes

Light-emitting diodes?LEDs?have the advantages of high luminous efficiency,long life,small size,and controllable emission wavelength.With the development of LED technology and the continuous decline of production costs,LED light sources are constantly replacing traditional light sources.From the ultraviolet region to the visible light region,and then to the infrared region,many kinds of LED have been produced as light sources.The technology of white LEDs is relatively mature by coating phosphor powder on blue LEDs.However,the light extraction efficiency of LED can be further improved,especially in the ultraviolet region.The transmittance of the indium tin oxide?ITO?decreased in the ultraviolet region,resulting in a decrease in the light extraction efficiency of the ultravoliet LED?UV LED?.In order to improve the light extraction efficiency of UV LED,this thesis used laser direct writing to fabricate micro/nano-structure,and investigate the influence of micro/nano-structure on light extraction efficiency of UV LED.The main research contents are shown as follows:?1?The effect of patterned ITO on the optical and electrical properties of UV LEDs was investigated in detail.Laser direct writing was used to fabricate patterned ITO structure,and several kinds of patterned ITO structures with different sizes and periods were designed and fabricated.Meanwhile,unpatterned ITO film was also fabricated for comparison.The transmittance of these patterned ITO structures and unpatterned ITO were measured using UV/VIS/NIR spectrometer.The light output power of UV LED as a function of injected current was measured to analyze the effect of patterned ITO on light output power of UV LED.?2?A high ultraviolet light transmittance and low sheet resistance metal wire grid transparent conductive electrode based on laser direct writing technology was proposed to improve the light extraction efficiency of theUV LED.Effect of period of Ni/Au wire grid on optical and electrical properties of UV LED was investigated.At the same wire width nearly 600 nm,the UV LED with small period of Ni/Au wire grid showed higher light output power?LOP?and lower forward voltage due to the lower sheet resistance and more uniform current spreading.Compared to Ni/Au wire grid,the UV LED with Ni/Au thin film transparent conductive electrode?TCE?showed LOP and lower forward voltage because of better current spreading,which indicated that current spreading was more important than the light absorption of the metal electrodes.In addition,the UV LED with ITO TCE exhibited a higher LOP than that of UV LED with Ni/Au thin film because of the high transmittance of ITO,which revealed that the transparency of material played a major role in improving the LOP when the Ni/Au thin film and ITO exhibited a similar current spreading.?3?A distributed Bragg reflector with double layer stacks structure was designed to increase the reflected bandwidth.Periods of TiO₂/SiO₂ stacks,thickness of metal film,and material of metallic reflector were designed and optimized in simulation software.The relationship between the reflectivity and reflectance bandwidth of the distributed Bragg reflector?DBR?and the number of DBR stacks were analyzed.The reflectivity and the reflectance bandwidth between single-layer DBR and double-layered DBR were compared.The number of DBR stacks were optimized to obtain the highest reflectivity and the largest reflectance bandwidth.Then,the reflectivity and reflectaice bandwidth of the hybrid DBR consisting of TiO₂/SiO₂ DBR and metal layer was investigated.Thickness of the metal layer was optimized and the reflectivity of different metal materials were compared to obtain the optimal hybrid DBR.Finally,the optimal reflectivity and reflectance bandwidth of hybrid DBR were obtained.