Structural Design And Characterization For Light Extraction In GaN-based LED Electrodes

We first investigated the fundamental properties of the III-nitride-based light emitting diodes (LEDs). It is worth noting that how to improve the light extraction efficiency (LEE) has become a critical issue for achieving high power LED devices. Indeed, there are numerous causes leading to the inferior LEE performance of such LEDs, especially for fabricating metallic electrodes based on complete structural LEDs, a further detailed analysis and improvement is necessary.In this work, the complete structural LEDs were epitaxially grown via metal organic vapor phase epitaxy (MOVPE) technology. Based on the high quality LED structures, a series of characterizations such as microscopic characterization, electroluminescence (EL) and photoluminescence (PL) as well as atomic force microscopy (AFM) measurements were carried out. All these above results reveal good performance of the epitaxial LED structures and provide basis for the device fabrication.Compared with the conventional disk-shaped electrodes, the micro-array electrodes structure were fabricated for UV and blue LEDs respectively. Through structural design and experimental fabrication of electrodes for UV-LEDs, it is found that the applied voltage exhibits a smaller turn-on and a larger current with array structures than samples that using the disk electrodes. On the other hand, the EL intensity as well as the fluorescence corresponding to the emission of MQWs exhibits stronger associated with a stronger dominant deep-level emission. Thus, the light extraction for UV-LEDs was enhanced by implementing a micro-array electrode structure. For blue LEDs, it is still confirmed that the enhancement of EL intensity and stable fluorescence with no other emission bands such as the deep-level emission were observed. The similar current-voltage property was also obtained, indicating more effective current injection and uniform distribution as well. The injected current is approximately with an enhancement of190in the array structure, in other words, if we keep on the same current density injected for disk-and micro-array structure electrodes, the luminescence intensity will be significantly enhanced in the array electrodes. Furthermore, the full width at half maximum (FWHM) of the MQW emission tends to be narrower leading to excellent device performances.In summary, we performed the micro-array conductive electrodes on top of the GaN-based LEDs for enhancing light extraction and lateral current distribution properties. The results show a smaller turn-on and enhanced luminescence intensity, as well as more uniform current injection in contrast to the conventional disk structure. By presenting theoretical analysis on the influence of surface plasmons and injected current diffusion, the current distribution were combined to light extraction results for further investigating the detailed mechanism.