ON THE CURRENT MECHANISM IN REVERSE-BIASED AMORPHOUS-SILICON SCHOTTKYCONTACTS .1. ZERO-BIAS BARRIER HEIGHTS AND CURRENT TRANSPORT MECHANISM

A study of the zero-bias barrier heights of hydrogenated amorphous-sil icon-based Schottky diodes and the prevailing current transport mechan isms in these structures is made using electrical and electro-optical techniques. Several series of devices were made using Cr, Mo, W, and P t as Schottky metals. The current-voltage characteristics of the devic es were obtained with their temperature dependence. The barrier height s were determined independently using internal photoemission experimen ts at three temperatures between 270 and 380 K. In devices where the S chottky barrier is deposited on top of the semiconductor material, the saturation current density is found to be most likely determined by c ombined drift and diffusion of the carriers. In devices where the Scho ttky barrier is formed at the bottom of the diode, the transport mecha nism tends towards thermionic (field) emission, but only slight effect s of the prevailing transport mechanism on the electrical performance of these diodes were observed. Also, in these devices a relatively def ect-rich a-Si:H layer at the bottom (Schottky) contact could be detect ed opto-electronically, which prohibited barrier height determination using internal photoemission. For the influence of the metal work func tion phi(m) on the electron-barrier height (phi(b) we obtain phi(b) = (0.10 +/- 0.02) phi(m) + (0.48 +/- 0.12), which is in good agreement w ith a previous determination of the dependence of the barrier for hole s on phi(m).