Introduction
GaN based power transistors can only gain market acceptance if they demonstrate switching properties superior to competing technologies. So far, mainly the improved static on-state resistance of these devices has been highlighted in literature demonstrating the principal suitability of GaN devices for power applications. According to Fig. 1 there is a tremendous advantage of GaN devices over Si devices in terms of the product “on-state resistance times gate charge” . This product can be considered as a figure of merit for switching efficiency. Any increase of Ron, for example due to dynamic switching effects, reduces the specific GaN advantages [1]–[4]. Indeed, dynamic switching properties of today's GaN power devices are often lagging behind significantly related to the performance expected from their DC parameters. The dynamic on-state resistance often scales exponentially with device switching voltage and thus significantly challenges high voltage GaN switching applications. A fundamental understanding of the physics responsible for this mechanism is indispensable for designing well justified technological countermeasures towards GaN high voltage switching devices.