Improved Performance of High-Voltage Vertical GaN LEDs via Modification of Micro-Cell Geometry

Abstract

Vertical-type high-voltage light-emitting diodes (HV-LEDs) with 2 × 2 micro-cells were fabricated on Cu substrates, and the micro-cell geometry was modified to enhance the optoelectronic performance. The current spreading in micro-cell is most dominantly affected by the distance between electrode and edge of chip. When square cells were combined in a HV-LED, the device performance was poor due to an obvious current-crowding phenomenon that occurred near the electrodes. This was attributed that the electrodes in these four square micro-cells were all far away from the edges, resulting in the severe current-crowding phenomenon. On the contrary, as the HV-LED was prepared with four rectangle, triangle, or L-shaped micro-cells, the electrodes were close to the edges of micro-cells and the current spreading effect can be easily improved. Although a HV-LED connected with L-shaped cells possessed a better current spreading effect and a lower surface temperature, the light extraction was relatively low because of an electrode-shading loss effect. When triangular cells were used to prepare the HV-LED, the device achieved a superior optoelectronic performance compared with that of other cells because of a lower current-crowding effect and a more uniform light emission. After an epoxy package process, a lower forward voltage of 14.9 V and a higher output power of 353.2 mW were obtained using this HV-LED at an injection current of 80 mA. Additionally, the wall-plug efficiencies of this device at 20 and 80 mA were 41.1% and 29.7%, respectively. The results confirm that the design of triangular cell is beneficial for enhancing the optoelectronic performance of HV-LEDs. Furthermore, the fabrication processes of vertical LEDs have high potential for HV-LED applications.

Multi-Azimuth Failure Mechanisms in Phosphor-Coated White LEDs by Current Aging Stresses

“…However, room for improvements remains, including the internal quantum efficiency of the active region [5,6], the light-extraction technology [7], the current-flow design [8,9], the minimization of resistive loss [10], the electrostatic discharge stability [11], and the color-rendering property via the color mixing [12,13]. Aside these improvements, it is known that, due to their importance, various stress-measured degradation tests, including thermal, electrical, static charges, and moisture, have been developed [14,15].…”

Multi-Azimuth Failure Mechanisms in Phosphor-Coated White LEDs by Current Aging Stresses

“…However, room for improvement remains, including the internal quantum efficiency of the active region [5,6], the light-extraction technology [7], the current-flow design [8], the minimization of resistive loss [9], the electrostatic discharge stability [10], and the color-rendering property via the color mixing [11]. Aside from these improvements, various stress-inducing degradation tests, by means of temperature, current, static charge, optical radiation, and moisture, have been developed [12][13][14].…”

Diffusion-Driven Charge Transport in Light Emitting Devices

“…The mechanisms of the efficiency droop in InGaN LEDs have been studied extensively, where carrier delocalization [ 21 , 22 , 23 ] and electron leakage [ 18 , 24 ] are proposed to be key reasons, while the most recent reports mainly pointing to Auger recombination as the main culprit [ 25 , 26 , 27 , 28 ]. Secondly, particularly in the modern high quantum efficiency LEDs, the efficiency droop limitations, current crowding and resistive loss become the most severe bottlenecks for high output power devices, confining their optimal high-efficiency performance at current densities well below 100 A/cm [ 29 , 30 , 31 , 32 , 33 , 34 ].…”