An investigation of the amorphous-silicon barrier and p-n junction

Abstract

With the growing interest in the properties and application of amorphous (a-) Si it is relevant to look in some detail into the formation and electronic properties of the amorphous barrier and p-n junction. In the first part of this paper a series of model calculations based on the experimentally determined density of state distribution in glow-discharge a-Si is presented. The net space charge in the barrier region is calculated as a function of energy for doped and undoped specimens. A step-by-step solution of Poisson's equation then leads to the barrier profile showing that the a-barrier for undoped and weakly doped specimens differs basically from its crystalline counterpart. The analysis is then extended to the amorphous p-n junction. In the second part of the paper the differential barrier capacitance, C, is calculated and its dependence on applied potentials and on frequency investigated. It is found that C‒V plots should be critically dependent on the measuring frequency because the latter determines the energy range of the localized states that can contribute to the barrier charge density. Agreement with preliminary experiments is encouraging. Finally, the interpretation of a-barrier capacitance measurements is discussed.