Speaker
Description
We investigated the nonlinear absorption behaviours in wide bandgap semiconductors such as silicon carbide, SiC and gallium nitride, GaN and explored their photophysics behind the electronic transitions. The former material is an indirect semiconductor while the latter is a direct semiconductor. Though their applications are more confined in comparison with the traditional silicon semiconductor, it can be found in high performance power electronics and demand is growing due to the rising popularity of electric vehicles and the rapid development of commercial satellites. To study the space radiation effects in these wide bandgap devices, typically heavy-ion beams are applied. However, instead of the conventional accelerator-based device testing, a picosecond/femtosecond pulsed laser can be used as an alternative high energy source to facilitate similar radiation effects based on the optical absorption in the semiconductor material. Besides evaluating the device susceptibility to radiation damage, a high resolution 2D/3D spatial mapping of sensitive regions in the circuitry can be extracted through raster-scanning the device under a pulsed laser beam tightly focused via high numerical aperture objective. This additional information can be difficult to obtain in heavy-ion testing. For the preliminary laser-based testing, commercial photodiodes were used as the sample devices to study their optical absorption characteristics in the infrared spectral regime. From the experiments, electron-hole pair generation was found to involve the absorption of multiple photons and, possibly, multiple phonons in relation to the indirect bandgap SiC. Thus, the feasibility of using an ultrafast infrared laser as the high energy source in simulating the radiation effects in wide bandgap devices is not unattainable. It offers an alternative way of fast device screening for defects. We will present full details of our experimental findings in the presentation.
