Power semiconductor devices are used for switching large loads in cars, trains, industrial applications or other fields of daily life. The harsh environmental conditions and the extended operation ranges in such applications are extreme and bring the classical semiconductor material Silicon to its physical limits. Due to their outstanding material properties, wide band gap materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) shift these physical limits to much higher values. However, the degradation mechanisms at high-voltage, high-power, high-temperature and/or high-current conditions have to be understood. By tracing down degradation under such conditions by various paths, one ends up at the smallest possible range, the atomic composition of the semiconductor material. Changes in the atomic structure of the materials, which build up the device, alter the macroscopic performance such as the threshold voltage or the drain current and eventually lead to device failure. These atomic transitions which impact the macroscopic behavior of a device are usually referred to microscopic defect creation and charging. Only few researchers are in the lucky position to work on such phenomena under harsh conditions...
To understand the impact of microscopic defects on the performance and reliability of wide band gap devices KAI established several electrical measurement and analysis approaches in the last years. Keywords for a few of the available approaches are on-chip polycrystalline silicon heater structures, charge pumping, impedance spectroscopy, deep level transient spectroscopy and many others.
In order to prevent future failures of power devices, exploring composition and properties of microscopic defects is crucial. Researchers do so by suggesting microscopic defect models and validating these models through sophisticated electrical measurements for differently processed devices.
Temperature is a key parameter in the behavior of crystal point defect creation and charging/discharging processes. By approaching the absolute zero point of temperature down to a few Kelvin, electronic process in a semiconductor become slower and slower. Processes which happen within a millionth or billionth of a second at room temperature now need seconds or minutes and thus become observable with electrical measurement equipment. Detailed analysis of the transient behavior at every temperature allows identification of electronic parameters and thus identification of the responsible point defects.