Light emitting diodes reliability review

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

A relatively small ESD protection diode is formed on the same chip as a light emitting diode. In one embodiment, the ESD diode is a mesa-type diode isolated from the light emitting diode by a trench. To reduce the series resistance of the ESD diode, the PN junction and metal contact to the semiconductor material is made long and expands virtually the width of the chip. Various configurations of the PN junction and the N and P metal contacts for the ESD diode are described for increasing the breakdown voltage and for improved testing.

LED chip with integrated fast switching diode for ESD protection

GaN-based light-emitting diodes (LEDs) with various p-cap layers were prepared It was found that surface morphologies of the LEDs with 800/spl deg/C grown cap layers were rough due to the low lateral growth rate of GaN It was also found that 20-mA forward voltage of the LED with 800/spl deg/C grown p-AlInGaN-GaN double-cap layer was only 305 V Furthermore, it was found that we could achieve a high output power and a long lifetime by using the 800/spl deg/C grown p-AlInGaN-GaN double-cap layer

Nitride-based LEDs with 800/spl deg/C grown p-AlInGaN-GaN double-cap layers

Nitride-based light-emitting diodes (LEDs) with textured side walls were fabricated. By using plasma-enhanced chemical vapor deposition SiO/sub 2/ layer as the etching mask, we successfully etched the nitride epitaxial layers to achieve wavelike side walls. It was found that such wavelike side walls could mainly enhance the light output at the horizontal directions. With a 20-mA current injection, it was found that the output powers of the LED with textured side walls and normal LED were 9.3 and 8.4 mW, respectively. Furthermore, it was found that such textured side walls will not result in a higher operation voltage.

Nitride-based LEDs with textured side walls

GaN Schottky diodes were built internally inside the GaN green LEDs by using etching and redeposition techniques. By properly selecting the etching areas underneath the bonding pads, one can minimize the optical loss due to the etching process. Although the reverse current and the forward turn-on voltage were both higher for the GaN LED with a Schottky diode, it was found that the internal Schottky diode could significantly increase the electrostatic discharge threshold from 450 to 1300 V.

C.H. Liu

Papers

Improved ESD protection by combining InGaN-GaN MQW LEDs with GaN Schottky diodes