UT researcher integrates silicon LED on chip for photonics

A PhD student from the University of Twente has found a way to combine a silicon LED with cmos technology. This makes it possible to create a light connection on chips, something that traditionally causes problems.

The method described by Satadal Dutta in his PhD research does not require any special materials or manufacturing techniques, which increases the chance that the research can be used in practice for photonics. Photonics has the potential to deliver faster and more economical chips, but an obstacle is that electronics and light are difficult to combine. Optical circuits are often based on materials such as indium phosphide and gallium arsenide, the University of Twente describes, but are therefore difficult to combine with cmos technology.

Dutta gets around this by using a silicon LED and using breakdown voltage to create the avalanche effect. This causes the LED to emit visible light, where silicon LEDs normally only emit infrared. The light can be directed to a silicon photodiode that can detect it. This means that the light source, the detector and the light-conducting channel can be made using the same technology as the electronics.

The combination measures a few tens of micrometers and is admittedly less economical than fully optical connections, but according to the university this outweighs the ability to combine the techniques and make circuits that work partly optically, partly electronically.

Dutta describes his method in his thesis ‘Avalanche-mode silicon LEDs for monolithic optical coupling in CMOS technology’. NXP, among others, supported him in the investigation.

Top and side view of the LED, light detector (PD) and light guide channel