AET develops vertical blue LEDs on GaAs
The VB-type blue LED chip has a p-side-down structure which can increase the effective conducting area of the p-electrode and reduce the series resistance effect of the thin p-layer. In addition, a thick n-type GaN window layer can be readily included to increase the light extraction from LED chips. The concept of thick window layers has already been adopted with great success in AlInGaP LED chips to enhance light extraction.
At 20mA, a conventional GaN-on-sapphire chip has a dominant wavelength of 470 nm, an operating voltage of 3.5V, and an output power of 2 mW. Under the same bias conditions, the VB-type LED chip shows the same dominant wavelength, a lower operating voltage of 3.3 V, and a 25% higher output power. The increase in brightness for the VB-type LED is due to more efficient current spreading and to the thick window layer.
AET Inc. was founded in October 1998 as a pure-play MOVPE and HVPE epiwafer supplier, but changed its strategy in late 2001 and started producing high brightness LED chips. The company is continuing to improve the performance of its VB-type blue LED chips, and engineering samples will be ready by the end of this quarter. AET Inc. has also obtained funding from the Ministry of Economic Affairs of Taiwan to develop GaN substrates; these are expected to be commercialized by the end of 2003.
