Intrinsic and Extrinsic Semiconductors

Abstract

Pure (intrinsic) semiconductor materials have an extremely limited range of applications in the fabrication of semiconductor devices. The reason for the development of solid-state electronics based on semiconductor materials since the late 1950’s is that the conductivity of semiconductors can be tuned with introducing small quantities of selected impurity atoms into pure semiconductors in a highly controlled methods. This precisely controlled introduction of a range of useful impurity atoms into a pure semiconductor is referred to as doping of an intrinsic semiconductor to have a doped or extrinsic semiconductor. The significance of being able to dope semiconductors in this way lies in the fact that extremely small dopant density of the appropriate elements are capable of producing relatively large, but controlled changes in the electrical conductivity of semiconductor materials. A potentially infinite range of selectively doped extrinsic semiconductors forms the material basis of all semiconductor devices. The electrical conductivity of a material is determined by two material parameters, namely free charge carrier density in the material and their respective mobilities. To understand the physical basis of semiconductor device operation, it is necessary to acquire knowledge on how free carrier density changes by the addition of dopant atoms to semiconductor materials.