On the current mechanism in reverse-biased amorphous-silicon Schottky contacts. I. Zero bias barrier heights and current transport mechanism

Abstract

A study of the zero-bias barrier heights of hydrogenated amorphous-silicon-based Schottky diodes and the prevailing current transport mechanisms in these structures is made using electrical and electro-optical techniques. Several series of devices were made using Cr, Mo, W, and Pt as Schottky metals. The current-voltage characteristics of the devices were obtained with their temperature dependence. The barrier heights were determined independently using internal photoemission experiments at three temperatures between 270 and 380 K. In devices where the Schottky barrier is deposited on top of the semiconductor material, the saturation current density is found to be most likely determined by combined drift and diffusion of the carriers. In devices where the Schottky barrier is formed at the bottom of the diode, the transport mechanism tends towards thermionic (field) emission, but only slight effects of the prevailing transport mechanism on the electrical performance of these diodes were observed. Also, in these devices a relatively defect-rich a-Si:H layer at the bottom (Schottky) contact could be detected opto-electronically, which prohibited barrier height determination using internal photoemission. For the influence of the metal work function φm on the electron-barrier height φb we obtain φb=(0.10±0.02)φm+(0.48±0.12), which is in good agreement with a previous determination of the dependence of the barrier for holes on φm.