High-quality, single-crystalline silicon-germanium (Si.sub.(1-x)Ge.sub.x) having a high germanium content is provided. Layers of the high-quality, single-crystalline silicon-germanium can be grown to high sub-critical thicknesses and then released from their growth substrates to provide Si.sub.(1-x)Ge.sub.x films without lattice mismatch-induced misfit dislocations or a mosaic distribution of crystallographic orientations.

A photovoltaic device includes a digital alloy buffer layer including a plurality of alternating layers of semiconductor material. An absorption layer epitaxially is grown on the digital alloy buffer layer, an intrinsic layer is formed on the absorption layer and a doped layer is formed on the intrinsic layer. A conductive contact is formed on the doped layer.

An avalanche photodiode includes a silicon layer on a substrate; a germanium layer on the silicon layer; a cathode and an anode on any of the silicon layer and the germanium layer; and a plurality of contacts on the germanium layer, in addition to the cathode and the anode. The silicon layer can include a highly doped region at each end, an intrinsic doped region in a middle, and an intermediately doped region between the highly doped region at each end and the intrinsic doped region, and the cathode and the anode are each at a respective a highly doped region at each end. The germanium layer can include a plurality of highly doped regions with each including one of the plurality of contacts.

A photovoltaic device is provided. It comprises at least two electrical contacts, p type dopants and n type dopants. It also comprises a bulk region and nanowires in an aligned array which contact the bulk region. All nanowires in the array have one predominant type of dopant, n or p, and at least a portion of the bulk region also comprises that predominant type of dopant. The portion of the bulk region comprising the predominant type of dopant typically contacts the nanowire array. The photovoltaic devices' p-n junction would then be found in the bulk region. The photovoltaic devices would commonly comprise silicon.

A photo-sensitive device includes a uniform layer, a gradated buffer layer over the uniform layer, a silicon layer over the gradated buffer layer, a photo-sensitive light-sensing region in the uniform layer and the silicon layer, a device layer on the silicon layer, and a carrier wafer bonded to the device layer.

An electrical device includes a counterdoped heterojunction selected from a group consisting of a pn junction or a p-i-n junction. The counterdoped junction includes a first semiconductor doped with one or more n-type primary dopant species and a second semiconductor doped with one or more p-type primary dopant species. The device also includes a first counterdoped component selected from a group consisting of the first semiconductor and the second semiconductor. The first counterdoped component is counterdoped with one or more counterdopant species that have a polarity opposite to the polarity of the primary dopant included in the first counterdoped component. Additionally, a level of the n-type primary dopant, p-type primary dopant, and the one or more counterdopant is selected to the counterdoped heterojunction provides amplification by a phonon assisted mechanism and the amplification has an onset voltage less than 1 V.

A solar cell comprising a bulk germanium silicon growth substrate; a diffused photoactive junction in the germanium silicon substrate; and a sequence of subcells grown over the substrate, with the first grown subcell either being lattice matched or lattice mis-matched to the growth substrate.

A semiconductor device comprises a plurality of quantum structures comprising predominantly germanium. The plurality of quantum structures are formed on a first semiconductor layer structure. The quantum structures of the plurality of quantum structures have a lateral dimension of less than 15 nm and an area density of at least 810.sup.11 quantum structures per cm.sup.2. The plurality of quantum structures are configured to emit light with a light emission maximum at a wavelength of between 2 m and 10 m or to absorb light with a light absorption maximum at a wavelength of between 2 m and 10 m.

A photodetector is provided. The photodetector includes a first electrode region in a semiconductor layer, a light absorption material on the semiconductor layer, and a second electrode region above the light absorption material. The light absorption material is electrically connected to the first electrode region through a first superlattice structure and electrically connected to the second electrode region through a second superlattice structure, and each of the first superlattice structure and the second superlattice structure includes multiple SiGe layers spaced apart from each other.

An avalanche photodiode includes a silicon layer on a substrate; a germanium layer on the silicon layer; and a plurality of contacts including a cathode, an anode, and at least two separate gain tuning contacts configured to adjust an electric field to tune multiplication of carriers. The at least two separate gain tuning contacts are configured to control the electric field in the germanium layer and silicon layer. The at least two separate gain tuning contacts are configured to tailor the electric field such that the multiplication of carriers is greater in the silicon layer than the germanium layer. This added gain tuning control can be used to tailor the electric field profile such that multiplication happens mostly in silicon to achieve lower excess noise and little to no bandwidth variation.