Elimination of random doping enables reproducible fabrication of quantum devices

A UNSW-led collaboration has found that removing random doping in quantum electronic devices dramatically improves their reproducibility – a key requirement for future applications such as quantum information processing and spintronics.

The challenge of quantum reproducibility

The challenge in manufacturing quantum devices is that until now it has not been possible to fabricate two quantum transistors with identical performance characteristics.

Although the devices appear to be physically identical, their electrical performance can vary widely from device to device. This makes it difficult to integrate multiple quantum components into a complete quantum circuit.

In the new study led by UNSW, researchers show that the problem lies with the random spatial position of dopants in quantum devices.

The classic approach to making semiconductors conductors of electricity is to chemically dope it with another element. For example, a very small amount of phosphorus atoms added to silicon produces an excess of free electrons, allowing an electric current to flow

But in nanoscale quantum devices, the random positioning of these dopants means that no device has identical characteristics.

The UNSW-led team worked with collaborators at Cambridge to show that removing dopants makes quantum devices significantly more reproducible.

Lead author Ashwin Srinivasan commented: “The electrical gain of undoped quantum point contact transistors is up to three times more uniform for the new approach, compared to conventional doped devices.”

Professor Hamilton, head of the Quantum Devices lab at UNSW, Sydney, said: “We had suspected that removing the random doping would improve the reproducibility of the device, but the results were much better than we expected. Ashwin made nine devices, and all of them were shown to have identical quantum properties and electrical performance. I had never seen anything like it before. This work shows that it is possible to manufacture quantum devices in a reproducible manner. “

Improving the reproducibility of quantum devices with completely undoped architectures has been published in Applied Physics Letters.