Novel Compound Semiconductor Devices for Digital Cryo-Electronics

About the project

About the Project Huge resources, both nationally and internationally, are being deployed for the development of quantum computing. While there are several different quantum computing platforms, one of the leading ones is based on superconducting qubits, because solid state solutions are more scalable. However, superconducting qubits require an awkward combination of mK temperatures and several RF signals per qubit to operate them. As the qubit count goes up, increasing numbers of carefully engineered RF lines are need to link room temperature to mK, which takes up space, is inefficient, expensive and a substantial heat leak. A far better solution is cryo-electronics, ultimately a cryo-, conventional, computer, as close to the quantum computer as possible, to interface with it and run it. With careful design and specifications conventional Si-based electronics can operate at several K, but will inevitably give out at lower temperatures. Semiconductors rely on doping to make even the most basic devices, and because dopants have ionisation energies of 10’s of meV, they don’t work well, or even at all, at low temperatures: the charge carriers ‘freeze out’. We are working on a novel approach to digital electronics [1], using compound semiconductors AlSb, GaSb and InAs, called the 6.1-Å family because of their very comparable lattice constants. Despite this structural similarity, they have very different band gaps and conduction and valence band offsets, which can be exploited to make devices with unique properties. To date, much of this work has focused on the development of ULTRA RAM ™ memory [2] and field-effect inverter (FEI) logic [3] at room temperature. However, as a direct consequence of the remarkable properties of the 6.1-Å semiconductors, our devices are made without doping. Instead, they rely on band offsets to provide charge carriers, making them capable of operating down to absolute zero. This PhD will be dedicated to the design, fabrication and testing of ULTRA RAM ™ and FEI-logic individual devices and simple integrated circuits for use at low temperatures. It will involve fine-tuning of device and array design to optimise low-temperature operation, fabrication in the QTC cleanrooms in Physics and room temperature and low temperature testing (in collaboration with Dr Michael Thompson and/or Prof Jon Prance).

Research areas