The CORPE (Center Of Reliable Power Electronics) project aims to improve the understanding of the failure modes and deterioration of power electronics components.
Power electronics is a term covering semiconductor components used for controlling electric power, typically large voltages and/or currents. Such components are used in wind turbine converters, solar cell inverters, electrical motor control, switch mode power supplies, electric grid converter bridges and in general almost everywhere where there is a need for voltage conversion or control. Needless to say it has a high impact to improve the reliability and predictability of these components.
As part of the CORPE project we are looking at the effect of the presence of defects in the base material used for manufacturing the power electronics semiconductor devices. The dominant material used is neutron transmutation doped (NTD) silicon since this material offers the necessary uniformity and low doping levels. The former feature ensures an even distribution of the current through the device while the latter is required to allow the blocking of high voltages. The NTD silicon is made by irradiating very pure silicon with neutrons at a nuclear reactor. Slow neutrons can be captured by the Si-30 making Si-31 which is unstable and will decay into P-31 thus doping the material with phosphorous. The fast neutrons will however introduce radiation damage that has to be removed by subsequent annealing. Despite the thermal treatment there may be some residual defects present which may be due to the neutron irradiation, the crystal growth or the presence of impurities.
Electrically active defects in the active region of a semiconductor device can cause unwanted leakage currents in the off state as well as increased development of heat in the on state due to recombination. This makes it important to understand the nature of defects that can be present as well as how to avoid such defects. Furthermore it is unknown how defects will evolve when subjected to large currents through the active region. These are the topics of the ongoing research related to power electronics in the semiconductor group.
