Multiple cell photoresponsive amorphous alloys and devices

Abstract

The production of improved multiple cell photoresponsive amorphous devices, such as photovoltaic, photoreceptive devices and the like; having improved wavelength threshold characteristics is made possible by adding one or more band gap adjusting elements to the alloys in one or more cells of the device. The adjusting element or elements are added at least to the active photoresponsive regions of amorphous cells containing silicon and fluorine, and preferably hydrogen. One adjusting element is germanium which narrows the band gap from that of the materials without the adjusting element incorporated therein. Other adjusting elements can be used such as carbon or nitrogen to increase the band gap. The silicon and adjusting elements are concurrently combined and deposited as amorphous alloys by vapor deposition, sputtering or glow discharge decomposition. The addition of fluorine bonding and electronegativity to the cell alloy acts as a compensating or altering element to reduce the density of states in the energy gap thereof. The fluorine bond strength allows the adjusting element(s) to be added to the alloy cells to adjust the band gap without reducing the electronic qualities of the cell alloy. Hydrogen also acts as a compensating or altering element to compliment fluorine when utilized therewith. The compensating or altering element(s) can be added to the alloy during deposition of the cells or following deposition. The addition of the adjusting element(s) to the cell alloys adjusts the band gap to a selected optimum wavelength threshold for particular cells to increase the photoabsorption efficiency to enhance the device photoresponsive without adding states in the gap of the cells which decrease the efficiency of the devices. The adjusting element(s) can be added in varying amounts, in discrete layers or in substantially constant amounts in the cell alloys.