5 March 2018 16:54

A novel use of X-ray photoelectron spectroscopy (XPS) is being pioneered by Lancaster physicists working with technology firm Kratos Analytical.

XPS has the potential to become an important technique in the development and production quality control of compound semiconductor devices such as vertical-cavity surface-emitting lasers (VCSELs). 

Compound semiconductors are becoming more common in modern devices, such computers and mobile phones, as they can add features and functionality demanded by consumers.  

The global compound semiconductor market was worth $66bn in 2016, and is predicted to be worth $143bn by 2023. 

But, despite the importance of elemental composition in compound semiconductors, its accurate determination remains a challenge, especially in devices where there are many different layers. 

Professor Manus Hayne from Lancaster University’s Department of Physics said: “XPS is used almost exclusively used on surfaces as it has an extremely small penetration depth into the material of only a few atomic layers. 

“However, by slowly and carefully etching the material in situ in the XPS machine we have shown that the technique can be applied to allow the accurate determination of the elemental composition of compound semiconductor materials with multiple layers of different alloys.” 

The ability to engineer the electronic and optical properties of compound semiconductors, for example in terms of their alloy composition, and grow multiple layers of different semiconductors on top of each other (heterostructures), is a key part of their success. 

Professor Hayne’s work with Kratos is an offshoot of his QR-SPLED project, funded through Innovate UK and the Engineering and Physical Sciences Research Council (EPSRC), in the framework of the UK National Quantum Technologies Programme. 

The project is assessing the feasibility of mass-producing low-cost, single-photon sources in the form of single-photon light emitting diodes (SPLEDs), by exploiting the unique properties of semiconductor nanostructures called self-assembled quantum rings. It follows on from a recent project in which Professor Hayne and collaborators demonstrated novel quantum-ring VCSELs. 

Professor Hayne is a world authority on self-assembled GaSb/GaAs quantum rings and their use in devices such as telecoms-wavelength VCSELs.