Abstract :
The Linvill models and the more conventional equivalent circuits can be used to make roughly equally accurate predictions of terminal behaviour of semiconductor devices. An extreme case, the diode storage time, illustrates this point. The principal feature of the Linvill models, not found in other models, is that current is expressed in terms of excess hole and electron densities. Specifically, the distributed current in a semiconductor device is approximated in the Linvill model by a finite number of currents in corresponding current nodes, and each of the nodes is associated with a particular elementary volume. The relation between the hole- and electron-charge density and the current in any elementary volume is represented by elements of a lumped equivalent circuit. When the models are applied to a practical problem, it is not possible to use the very large number of lumped elements which would be needed closely to model the distributed current, and a small number of model elements is used. In such a ?simplified? model, the one-to-one correspondence between model space and device space is obscure, and, furthermore, conditions based on this correspondence are not sufficient to obtain correctly the model element values. Using, in the last analysis, arbitrary configurations, the model elements must be calculated in such a manner that they match some set of terminal characteristics. A further practical drawback is that the lumped elements cannot be measured directly because they are expressible in terms of hole and electron concentrations, themselves not measurable. Without altering the intent of the Linvill approach, both of the above difficulties can be mitigated. One can represent the currents in the device by an alternative set of lumped elements in which the notion of volume is absent. Such elements are not necessarily associated with physical volumes and no contradictions are encountered with the simplified models. The alternative set of elements proposed in th- is paper can, furthermore, often be measured in terms of current and voltage. A last by no means negligible advantage is that a special symbolism is not required.
