On the Role of Inversion Layer, Electronic Density of States and Interfacial Layer on the Barrier Height Formation of Amorphous-Silicon Schottky Diodes

Abstract

Large variations in barrier height of a-Si:H Schottky diodes can be achieved by introducing thin inversion layer at the interface. Electronic density of states in the basic film depends upon the growth and surface preparation conditions.However, the high density of surface states of the order of 10 13 cm -2 eV -1 usually found at a-Si:H film masks the role of bulk density of states which are ∼10 16 cm -3 eV -1 . As the density of surface states increases, the barrier height increases. At very large density (∼ 5 × 10 14 cm -2 eV -1 ), Fermi level of the film pins to the neutral level and the barrier height becomes independent of the metal work function. Poisson's equation has been employed to illustrate the role of various charges contributed by the basic semiconductor, the inversion layer and the eletronic states. The concept of interfacial layer of 2 to 3 atomic dimensions with the permittivity of free space is essential to understand the mechanism of barrier height formation in a-Si:H Schottky diodes like similar devices in other semiconductors.