Dr Gunnar Kusch

Characterisation, Manipulation, and Design of Defects in Semiconductors

Defects in semiconductors are crucial for determining device performance. By understanding and controlling the population and type of these defects, we can create new opportunities for advanced device design and innovate semiconductor based technologies.

Porous AlGaN

Our research explores the utilization of extended defects and controlled doping levels to create porous AlGaN materials. The introduction of porosity provides an additional engineering parameter, allowing me to enable otherwise hard to achieve device structures and designs. 
I am particularly interested on using porous AlGaN to enable high efficiency UV-B devices, which will help, among other things, to create new and improved medical devices for treatment of psoriasis and other skin diseases. The current low output power of UV-B LEDs is to a considerable extent due to the lack of high quality templates. The available templates are either leading to relaxation, creating detrimental defects, or exhibiting significant surface roughness, inducing inhomogeneities. Porous material has been shown to aid in lattice relaxation, an instrumental effect in achieving red InxGa1-xN LEDs, presenting a new possible template opportunity for UV-B materials. These improved templates will significantly enhance the performance and reliability of UV-B LED devices.

An Atom at a Time: Characterisation of Point Defects

Optical characterisation of point defects in semiconductors has been limited by the spatial resolution of standard techniques. This limitation means that only ensemble information about point defects is available, with no insight into their nanoscale behaviour.
My vision is to create a novel capability for characterizing point defect ensembles on the nanoscale as well as the full opto-electronic properties of single, isolated point defects based on hyperspectral time-resolved cathodoluminescence (TR-CL) in a scanning electron microscope. Recent developments by me and other research groups show that TR-CL is the ideal technique to provide the capability to close the knowledge gap of the behavior of point defects on the nanoscale. While the underlying measurement principle is similar to that of the established TR-PL technique - measuring transient lifetimes from which the point defect properties can be inferred - TR-CL not only offers a significantly higher spatial resolution, well below the optical diffraction limit, but is also capable of providing the excitation energy to excite even the widest bandgap semiconducting materials. Additionally, TR-CL is able to combine those aspects with a temporal measurement resolution of the order of 10 ps, across a wide spectral range (200 nm to 850 nm), making it capable of investigating optical transient spectra across a broad range of materials, enabling new opportunities to quantify and qualify point defects by their impact on localized carrier dynamics.