On a semiconductor chip, one essential element is missing: a lightsource. An integrated lightsource can be very useful, however. In optical telecommunications, for example, or in lab-on-a-chip applications. University of Twente’s Phuong Le Minh developed a nanoscale integrated lightsourse. The principle of this tiny light source was discoverd by coincidence, performing semiconductor breakdown experiments. Le Minh succeeded in fabricating a micro channel

The nano-lightsource is formed by ‘controlled breakdown’ of the isolating oxide layer in a semiconductor device. At this moment, a tiny cell is formed working as a memory cell and as a light source as well, called an antifuse. The research group Semiconductor Components, of which Le Minh is a member, takes a lot of effort in investigating transistor reliability. In their experiments, the new ‘devices’ emitted light. What started as a surprising side-effect, could be transformed into a working nano-lamp. Le Minh has focused on applications in ‘microfluidics’: he has integrated the lightsource and a photodetector with a micron-size fluid channel and is able to distinguish various fluids going through. It is a very useful new part of a laboratory on a chip.

Apart from these lab-on-a-chip applications, research in optical telecommunications is focused on an ‘all-optical’ signal path, thus avoiding conversion losses, from optical to electronic vice versa. An integrated lightsource is very welcome there, as a new component. Silicon has excellent properties for a broad range of applications, but it is a very bad photon emitter: it is hard to fabricate an efficient light source in silicon. Coupling an external lightsource to a chip is a true piece of art as well: the system gets more voluminous than wanted, and coupling losses may appear. There is a worldwide quest for ‘solid state lighting’.

The lightsource is placed above the microchannel in a chip, with a photo detector on the bottomside of it. Detecting interference patterns, information can be retrieved about the fluid going through the channel. According to Le Minh, it is a step forward in the development of nano-lamps for various applications. He has performed his PhD research within the MESA+ research institute of the University of Twente, www.mesaplus.utwente.nl