SiGe photodiode
The lattice mismatching between a Ge layer and a Si layer is as large as about 4%. Thus, when the Ge layer is grown on the Si layer, penetration dislocation is introduced to cause leakage current at the p-i-n junction. Thereby, the photo-detection sensitivity is reduced, and the reliability of the element is also lowered. Further, in the connection with a Si waveguide, there are also problems of the reflection loss due to the difference in refractive index between Si and Ge, and of the absorption loss caused by a metal electrode. In order to solve said problems, according to the present invention, there is provided a vertical type pin-SiGe photodiode having a structure which is embedded in a groove formed in a part of a Si layer, in which a p-type or n-type doped layer is formed in a lower section of the groove, and in which a i-SiGe layer having a rectangular shape or a reverse tapered shape is formed on a layered structure formed by laminating a i-Si layer and a SiGe buffer layer on the lower section and the side wall of the groove. Further, in an optical connection section with a Si waveguide, impedance matching is effected by the layered structure composed of the i-Si layer and the SiGe buffer layer, and an upper metal layer is separated therefrom so that a poly-Si bridge structure is employed to electrically connect the upper metal layer therewith.
1. A SiGe photodiode, which is a p-i-n type photodiode composed of a Si x Ge 1-x semiconductor absorption layer, an upper electrode layer provided on the top face thereof, and a lower electrode layer provided under the rear face thereof,
wherein
the p-i-n type photodiode has a structure in which the Si x Ge 1-x semiconductor absorption layer is embedded in a groove formed in a part of a Si layer, and which comprises:
a p-type or n-type doped lower electrode layer which is formed in a lower section of the groove;
a layered structure composed of, a Si semiconductor layer and a SiGe buffer layer, which structure is formed on the lower section and the side wall of the groove;
the Si x Ge 1-x semiconductor absorption layer which is formed on the layered structure; and
a n-type or p-type doped upper electrode layer which is formed in an upper section of the groove.
2. The SiGe photodiode according to claim 1 ,
wherein the upper electrode layer is formed on the top surface of the Si x Ge 1-x semiconductor absorption layer, and
wherein the area size S upper-electrode layer of the upper electrode layer and the area size S bottom surface of the bottom surface of the Si x Ge 1-x semiconductor absorption layer are selected so as to satisfy the relationship of S bottom surface >S upper-electrode layer .
3. The SiGe photodiode according to claim 1 ,
wherein the p-i-n type photodiode is optically connected to a Si waveguide, and
wherein, when the Si x Ge 1-x semiconductor absorption layer is optically connected to the Si waveguide via the layered structure of the Si intrinsic semiconductor layer and the SiGe buffer layer, impedance matching is effected at the optical connection portion.
4. The SiGe photodiode according to claim 1 ,
wherein the upper electrode layer is electrically connected to an upper metal electrode layer, and
wherein the electric connection between the upper electrode layer and the upper metal electrode layer is achieved by a bridge structure made of polycrystalline Si.
5. The SiGe photodiode according to claim 4 ,
wherein the bridge structure made of polycrystalline Si is composed of a polycrystalline Si bridge array, and
wherein the polycrystalline Si bridge array has a structure in which a plurality of polycrystalline Si bridges are periodically arranged, and in which the selection of a wavelength region is made by the periodic structure.
6. An optical wiring system on an LSI, comprising, as a photo-detection section, the SiGe photodiode according to claim 1 .
7. An optical interconnection module comprising: a Si substrate in which the SiGe photodiode according to claim 1 is formed; and an LSI electronic circuit which is formed on the Si substrate monolithically with the photodiode.
8. The SiGe photodiode according to claim 2 ,
wherein the layered structure composed of the Si semiconductor layer and the SiGe buffer layer, which structure is formed on the lower section and the side wall of the groove, is a layered structure formed by laminating the Si intrinsic semiconductor and the SiGe buffer layer.
9. The SiGe photodiode according to claim 2 ,
wherein the Si x Ge 1-x semiconductor absorption layer which is formed on the layered structure is the Si x Ge 1-x semiconductor absorption layer having a rectangular shape or a reverse tapered shape.