PRESSURE EFFECTS ON ELECTRICAL AND OPTICAL-PROPERTIES OF SI-AS-TE CHALCOGENIDE GLASSES FABRICATED IN THE GRAVITY ENVIRONMENT AND IN A MICROGRAVITY ENVIRONMENT

Pressure-induced changes in the electrical resistivity and optical-abs orption spectrum have been studied for two kinds of Si9As14Te21 ternar y chalcogenide amorphous semiconductor samples fabricated in a microgr avity environment and under the gravity environment of the earth. Band gap narrowing occurs for both materials as is found commonly in chalc ogenide glasses, whereas the change is less pronounced for the space-m ade material than for the terrestrial-made material. A significant dif ference is found in the pressure-induced change of the optical Urbach energy, that is, it increases for the space-made material but decrease s for the terrestrial-made material in the low-pressure regime. These observations are accounted for upon assuming that the origin of the el ectronic states at the top of the valence band differs for these two m aterials although the material composition is identical.