For circuits such as switching power supply circuits and inverter circuits, semiconductor devices such as switching devices and diodes are used. Such semiconductor devices are required to have high breakdown voltage and low on-resistance. There is a trade-off relationship determined by device materials between the breakdown voltage and the on-resistance.
With the advancement in development of technology, low on-resistance for semiconductor devices has been realized down to the limit of silicon which is a major device material. In order to further improve the breakdown voltage and further reduce the on-resistance, it is necessary to change the device materials. By using GaN-based semiconductors such as GaN and AlGaN as switching device materials, it is possible to improve the trade-off relationship determined by the materials and to achieve rapidly-progressive high breakdown voltage and low on-resistance.
However, for example, in a switching device using a GaN-based semiconductor, there is a problem of “current collapse” in which on-resistance increases when a high drain voltage is applied.