Deepening our understanding of how and where electrons scatter in conventional electronic devices such as transistors, diodes, and LEDs, has been critical for meeting the ever-increasing demand for greater miniaturization, functionality, and energy efficiency of solid-state devices. Similarly, in quantum devices, where performance relies on manipulating the phase coherence of single electrons, photons, phonons, it is vital to understand how the wave-like scattering of matter is impacted by bandstructure, reflection at interfaces, finite-size effects, doping, and disorder.
The Quantum Device Microscope (QDM) is designed to visualize these effects by pinpointing where charge flow is enhanced/impeded using a sharp metallic stylus, and correlating this with other features (topographic/electrostatic) in the device.
The need for QDM?
In a typical device development process, the performance is tested in initial trial devices, usually described by a lithography layout and set of functional and atomic-scale requirements of the planar and vertical structure of materials. During device manufacture these materials and interfaces are exposed to chemical and thermal environments that can cause damage or unwanted changes that prevent basic characterisation. A powerful arsenal of standard characterisation techniques can be deployed to identify these events/processes and develop mitigation strategies. Once a viable trial device has been made, measurements are used to assess the device and benchmark various figures of merit. Growth conditions and lithographic designs are revised based on these measurements, and the cycle proceeds until device meets the target performance. Crucial figures-of-merit about quantum performance, however, escape optimisation because they are only accessible at mK temperatures, when momentum relaxation and phase breaking processes, electron-phonon and electron-electron scattering, are suppressed. The QDM meets the need for critical in-operando insights about factors affecting device performance at mK temperatures. Examples include imaging localized states that induce scattering and device instability in semiconductor-based qubits, imaging two-level systems responsible for losses in superconducting microwave circuits, and identifying edge states in topological devices
Current Projects:
- Imaging Andreev bound states in super-semi nanowires
- Scattering in topological insulators
- Edge channels in magnetic topological insulators (MAGMA)