Study On Design And Manufacturing Technology Of GaN-Based Light-Emitting Diodes With Superior Current Spreading

GaN-based light-emitting diodes?LEDs?have been used for numbers of applications such as solid-state lighting,automotive lighting,full-color displays,visible light communications,and biomedical instrumentation.Generally,due to the insulating property of the sapphire substrate,both n-/p-electrodes of lateral structure GaN-based LEDs are fabricated on the same side of the GaN epitaxial layers.Currently,both internal quantum efficiency and light extraction efficiency of LEDs have been significantly enhanced,yet current spreading in lateral structure GaN-based LEDs is a crucial issue.Moreover,because of the larger size and higher injection current of high power lateral structure LEDs,the current crowding phenomenon will be more conspicuous.In order to improve the optical and electrical properties of GaN-based lateral structure blue LEDs,the current spreading theorical model of LEDs and three types of lateral structure LEDs with superior current spreading were investigated in this thesis.?1?The current spreading theoretical model of GaN-based lateral structure LED chips was analyzed systematically.We developed a three-dimensional electrical-optical coupling model of LED.Additionally,the influence of ITO transparent conductive layer,SiO₂ current blocking layer?CBL?,the sheet resistance of n-GaN and ITO on current spreading performance of GaN-based lateral structure high-power blue LED was analyzed by using SimuLED commercial simulation software.?2?Combined with current spreading theoretical model,we designed an interdigitated SiO₂ CBL which was inserted between ITO transparent conductive layer and p-GaN layer to improve current spreading of the fabricated lateral structure high-power blue LEDs.The SiO₂ film was deposited by plasma enhanced chemical vapor deposition?PECVD?.Furthermore,effects of reaction parameters such as the ratio of reactive gases,RF power,reaction chamber pressure and temperature on the deposition rate and refractive index of SiO₂ films were also investigated.The results showed that the designed SiO₂ CBL could significantly alleviate current crowding around the p-electrode,resulting in an improved external quantum efficiency of 18.7%for high-power LED at 350mA injection current.?3?A ring-shaped SiO₂ CBL was designed and fabricated to improve current spreading of lateral structure high-power bule LEDs.Subsequently,we also analyzed the effect of SiO₂ CBL thickness on high-power blue LEDs.In order to allow for the formation of continuous ITO film along sidewalls of SiO₂ CBL,the SiO₂ CBL?190nm?with inclined sidewalls was formed by combining thermally reflowed photoresist technique and inductively coupled plasma etching.It was found that the external quantum efficiency of the fabricated high power LEDs enhanced with increasing thickness of SiO₂ CBL.The external quantum efficiency of high power LED was improved by 12.7%when the thickness of the ring-shaped SiO₂ CBL is 190 nm.?4?GaN-based blue LEDs with patterned SiO₂ CBL and patterned ITO transparent conductive layer were investigated.The patterned SiO₂ layer,which served as CBL and passivation layer,was formed between ITO and electrodes.In addition,the patterned ITO was also performed in order to improve scattering probability of light emitted from multiple quantum wells,resulting in the enhanced light extraction efficiency due to a decreased light absorption by opaque electrode.The results showed that the external quantum efficiency of the LED was enhanced by13.8%at 200 mA due to the use of patterned SiO₂ CBL and patterned ITO.