Using a mathematical model of an electrical component, device, circuit, or system to determine the performance of the real physical entity.

• • Equivalent-circuit modelling uses standard circuit elements – resistors, capacitors, voltage and current sources, etc. – to represent the electrical behaviour of transistors and other active devices and circuits, the behaviour being described by the semiconductor device physics. Thus straightforward circuit theory is used to model the physical behaviour of these devices and circuits.

• • Physical modelling uses the semiconductor equations describing drift and diffusion current flows, continuity equation, Poisson’s equation, etc., to describe the movement of the charge carriers within the semiconductor device, and hence describe the external current-voltage behaviour. Further detail can be incorporated at the quantum mechanical level for those devices where such phenomena play a role in their electrical behaviour (in the high electron mobility transistor or in nanoelectronics, for example).

The modelling itself can be analytical, though nowadays greater emphasis is placed on numerical modelling, which can be incorporated into computer-aided design (CAD) software.