A semiconductive junction device comprises a thin layer of a glassy amorphous material exhibiting one type of conductivity (either N or P) disposed upon a semiconductive substrate possessing the other kind of conductivity. The glassy layer is sufficiently thin that it exhibits a useful level of conductivity. Preferably, the glassy layer is ion impermeable so that the device remains stable under a wide range of operating conditions. These junctions behave as diodes and can be incorporated in a wide variety of complex semiconductive devices.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser. No. 122,420 filed by the same inventor on March 9, 1971 now abandoned.
A semiconductive heterojunction device particularly useful as a photovoltaic device such as a solar cell comprises a heterojunction formed between a first layer of semiconductor material exhibiting one type of electronic conductivity (N or P) and a second layer of a compositionally different material exhibiting the other type of electronic conductivity (P or N), which second layer has an energy bandgap relatively wider than that of the semiconductor material and an electron affinity less than or equal to the electron affinity of the semiconductor. Preferably, the wider bandgap material is a glassy amorphous material which possess or is doped to possess a low resistivity below about 10.sup.7 ohm-cm. In devices employing N-type wider bandgap layers, the conduction band energy level of the wider bandgap material is preferably at substantially the same energy level as the conduction band energy level of the narrower bandgap material at electrical neutrality. In devices employing P-type wider bandgap layers, the valence band energy level of the wider bandgap material is preferably at substantially the same energy level as the valance band energy level of the narrower bandgap material.
A method is described for fabricating electroluminescent devices exhibiting visible electroluminescence at room temperature, where the devices include at least one doped layer of amorphous hydrogenated silicon (a-Si:H). The a-Si:H layer is deposited on a substrate by homogeneous chemical vapor deposition (H-CVD) in which the substrate is held at a temperature lower than about 200.degree. C. and the a-Si:H layer is doped in-situ during deposition, the amount of hydrogen incorporated in the deposited layer being 12-50 atomic percent. The bandgap of the a-Si:H layer is between 1.6 and 2.6 eV, and in preferrable embodiments is between 2.0 and 2.6 eV. The conductivity of the a-Si:H layer is chosen in accordance with device requirements, and can be 10.sup.16 -10.sup.19 carriers/cm.sup.2. The bandgap of the a-Si:H layer depends at least in part on the temperature of the substrate on which the layer is deposited, and can be "tuned" by changing the substrate temperature.
A multijunction photovoltaic device includes first, second, and third amorphous silicon p-i-n photovoltaic cells in a stacked arrangement. The intrinsic layers of the second and third cells are formed of a-SiGe alloys with differing ratios of Ge such that the bandgap of the intrinsic layers respectively decrease from the first uppermost cell to the third lowermost cell. An interface layer, composed of a doped silicon compound, is disposed between the two cells and has a lower bandgap than the respective n- and p-type adjacent layers of the first and second cells. The interface layer forms an ohmic contact with the one of the adjacent cell layers of the same conductivity type, and a tunnel junction with the other of the adjacent cell layers.
