A MONTE‐CARLO PARTICLE MODEL AND ITS APPLICATION TO A STUDY OF THE INFLUENCE OF THE DOPING PROFILES ON THE CHARACTERISTICS OF FIELD‐EFFECT TRANSISTORS

Abstract

The Monte‐Carlo particle model is a technique of simulating small semiconductor devices. It consists briefly of following the detailed transport histories of individual carriers, their time of free flight and consequent scattering chosen by a random number technique. A description of the method is given. The method has proved itself successful in semiconductor analysis, and as an example of its application we are using it to study the influence the epitaxial doping has on the performance of field‐effect transistors. We are comparing a transistor with an epitaxially grown active layer, with one with an ion implanted active layer and with an ideal device with an abrupt transition between the epilayer and the substrate. The cut‐off bias for ideal transistor is found to be more sharply defined than for the other two types of transistors. The spatial distribution of the carriers follows roughly the doping profile near the source. Underneath the gate the peak of the carrier density is pushed further down and into the substrate as the gate bias increases. This peak also weakens as the gate bias rises, and vanishes at, and beyond cut‐off. In the high field region after the gate the upper valleys population increases with increased drain bias and decreases with increased gate bias. The power gain and the y‐parameters are examined for all devices, both near pinch‐off and for no external gate bias. In both cases the ion implanted transistor shows the greatest gain. This transistor also exhibits the lowest minimum noise figure.