Compensating semiconductor materials

#This invention is in the field of semiconductor materials and more specifically semiconductor materials for photovoltaic cells.

#Photovoltaic cells have been developed which generate electrical energy directly from sunlight. Typically, such cells have been fabricated from semiconductor materials containing a rectifying junction, such as a p-n junction or a Schottky barrier.

#A number of problems have been encountered, however, in attempts to produce photovoltaic cells which would have wide acceptance for use in producing energy from sunlight. One of the problems has been the cost of producing such cells, which has heretofore been relatively high. In fact, the cost of photovoltaic cells has generally been considered to be severely limiting except in applications where cost is not a controlling factor, such as in space applications or generation of power in remote areas.

#FIG. 1 is a cross-sectional view of a photovoltaic device employing polycrystalline materials suitably doped to provide a rectifying junction and containing grain boundaries passivated in accordance with the invention.

#FIG. 2 is an enlarged view of the section circled in FIG. 1.

#FIG. 3 is a schematic view of a photovoltaic cell in accordance with the invention.

#Preferred embodiments of this invention will now be described in more detail with reference to the Figures.

#FIG. 1 illustrates a photovoltaic device, based upon a rectifying junction 15 formed in polycrystalline semiconductor material. The device has a conducting substrate 10, which may be formed from a material such as graphite, molybdenum or tungsten. In some cases, the semiconductor itself can serve as a conducting substrate if it is appropriately doped. Successive layers 12, 14 and 16, respectively, of p.sup.+ -semiconductor material, p-semiconductor material, and n.sup.+ -semiconductor material, respectively, are deposited upon conducting substrate 10 by well known processes. Semiconductor layers 12, 14, and 16 are preferably formed from gallium arsenide, suitably doped to provide the desired electrical properties. Thus, semiconductor layer 12 may be gallium arsenide suitably doped with p-dopants such as zinc, cadmium, beryllium or magnesium to a carrier level of 10.sup.18 CC.sup.-1 or above; semiconductor layer 14 may be a gallium arsenide layer suitably doped with p-dopants to a carrier level of 10.sup.16 -10.sup.17 ; CC.sup.-1 and n.sup.+ -semiconductor layer 16 may be gallium arsenide suitably doped with n-dopants such as sulfur, selenium or silicon to a carrier concentration of 10.sup.17 CC.sup.-1 or above.

#Grain boundaries or other dislocation defects form interstices 22 which extend through each of semiconductor layers 12, 14 and 16. Such interstices may originate in p.sup.+ -semiconductor layer 12, which is formed from polycrystalline material, and extend through layers 14 and 16. These interstices produce a shorting effect across junction 15. Thus, the open circuit voltage of the device is significantly less than would be the case if such grain boundaries were not present, and this results in a much lower photovoltaic conversion efficiency.