Quantum cascade lasers could help transistors become more energy efficient

Quantum cascade lasers could allow the ever-smaller transistors to operate at low power and lower temperatures without the problems associated with conventional designs.

Transistors produce the binary computer system’s ones and zeros by applying an electrical field that either halts or allows current to flow. One is typically current on, and zero is current off, but it is more likely zero is a lower current due to a lesser electrical field from a reduced voltage. As transistors have shrunk voltages have decreased, but as electronics heat up the system noise can obscure the one and zero current difference. A solution is to also use quantum cascade lasers to act as a one, zero switch, so the current can be small and still detectable.

“We have found a new way that takes the concept of layers but applies it in such a way that the [conventional] field effect [transistor] switching is still applicable, so it is compatible with existing transistor technology,” said Tillmann Kubis, a research assistant professor in Purdue University's school of electrical and computer engineering. Kubis’ job is the modelling of nanoscale phenomena and the discovery of this quantum cascade laser, conventional transistor technology combination was, “more of an accidental side product of our work on transistors in general and the modelling of that”.

The accidental discovery of the quantum cascade laser, conventional transistor technology combination occurred, “about January,” this year, according to Kubis. The cascade quantum laser uses nanoscale layers, several thousand, with different materials and through this structure the electrons cascade to eventually become photons. The photons act as the switch and this laser switch can be used at the same time as the conventional transistor switch where a current induced field is applied or not. “The total transistor becomes more sensitive to your switching operation,” Kubis adds.

This image shows a traditional silicon/germanium nanotransistor in atomic resolution with source, drain and gate contacts to control the charge flow. Purdue University researchers have developed transistor technology that shows potential for improving computers and mobile phones. Credit: Daniel Mejia

Kubis sees this concept as an advance on the other nano-transistor technologies that are being developed. “They all face the challenge of, you want a significantly high enough on-current, the one state, so that you can distinguish with back ground noise even when the transistor is hot.” He points to the need for these designs to have a huge difference between the current densities of one and zero, a four to five times magnitude difference. He also said that there had been attempts to create nanoscale layered transistors, but they had no progressed.

Kubis would be happy to take his cascade laser, conventional transistor concept further, but a funding partner is needed. The priorities of the funding partner would also help decide how the concept should become a working design. “There is some design work necessary to have a convincing prototype,” he explains. “We need to decide if it is for low power or rapid switching. We are looking for a funding source that would help us decide what the application is, and therefore the design.” The Purdue Office of Technology Commercialization helped file a patent application for the technology.

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