ABSTRACT
The essence of the power device is its switch function, which can go back and forth between on-state and off-state. The ideal device behaves like a metal bar in the on-state and acts as an insulator in the off-state. A power device gets the voltage-holding ability by having a high resistive region as an insulator. And its current-conducting ability can be expressed as Ohm's on the whole. However, the diffusion current becomes dominant under a low- current operation. The free electron's motion breeds an electric current in the semiconductor. This can be increased or removed by adding the forward or reverse voltage. The region's vanishing "free electrons" can become excellent insulators, offering a resistance of more than several hundred M^cm with silicon, for instance. Furthermore, the traditional semiconductor theory intends for low-voltage, low-current-density operation or high-frequency operation, which were possible by the semiconductor element when it was announced.
