“STUDY AND REALIZATION OF SCHOTTKY BARRIER PHOTODIODES IN HYDROGENATED AMORPHOUS SILICON”

Thesis for the Laurea Degree

by

The University of Rome “La Sapienza”

(1983)

Thesis advisor: Dr. Piero Migliorato

Candidate: Alessandro Lucchesini

Opposer: Prof. Umberto Maria Grassano

SUMMARY

The present work concerns the realization and the study of hydrogenated amorphous-silicon (a-Si:H) metal-semiconductor (M-S) photodiodes. This type of semiconductor recently gained a great importance in the field of the solid-state electronic devices such as solar cells, field effect transistors, and image sensors. The M-S diodes on a-Si:H used as solar cells show potential advantages against the classical p-n junctions for the simplicity of realization. The reproducibility and the difficulty in obtaining low reverse currents are still open problems.

Beside conventional M-S diodes, new type of devices has been made in the present work. These consist of a thin layer (l00 ¸ 200 Å) of hydrogenated amorphous silicon-carbide (a-SiC:H) between the metal and the a-Si:H. The aim of the a-SiC:H layer is twofold: firstly it allows obtaining low reverse currents (~10^-10A/cm²) with good reproducibility; secondly it makes the diode spectral response to depend greatly on the applied inverse voltage. This property can have application in the detection of colors images.

The experimental work is based on the preparation of the samples by utilizing the device for the thin films growth that has been set up previously in the laboratory and on the characterization of the transport and photo-transport properties of the obtained diodes. The experimental results are discussed on the base of the charge transport diffusion theory in metal-semiconductor junctions by the introduction of suitable modifications to adapt the theory to the amorphous materials.