thickness of 2 µm or more is required for use as a photoactive layer. Therefore, a very high forming speed is required for production. However, such forming speed cannot currently be achieved while maintaining good characteristics.
To solve these problems, this invention uses MC SiGe with a greater light absorption coefficient than MC Si, and makes a thinner photoactive layer. However, in order to make the photoactive layer 1 µm thick or less, the light absorption coefficient of the MC-SiGe must be at least three times as great as of the MC-Si. To achieve this, the composition ratio of Ge in the MC SiGe should be 20 at% or more.
This new device comprises a supporting substrate, a first electrode on the supporting substrate, a semiconductor layer (including a photoactive layer) on this electrode, and a second electrode on the semiconductor layer. The photoactive layer is a MC-SiGe layer with a Ge composition ratio of 20-40 at%; the signal intensity of the Ge-Ge bond is 30-60% of the signal intensity of an Si-Si bond observed by Raman spectroscopy, and the signal intensity of the Si-Ge bond lies in between. The thickness of the photoactive layer is 1 µm or less.
A PV device with this structure using thin MC-SiGe as the photoactive layer can provide good conversion efficiency.