Special Types of Field-Effect Transistors

Abstract

In 1950 Shockley succeeded in overcoming the earlier difficulties caused by the influence of surface states which had until then prevented a practical field-effect transistor. He used a pn junction gate to eliminate the effect of the surface states. The main advantage of such transistors compared to MOS transistors is their low 1 /f noise. The reason for this is that in an MOS transistor the current flows in a very thin surface layer and is therefore very sensitive to temporary surface charges. In a JFET the current flows in a channel which may be so far away from the surface that its effect is negligible. Such transistors are therefore used primarily in low noise applications.