Patent ID: 8859886

Claim:
A method for fabricating a multijunction solar cell, comprising: providing a germanium substrate comprising germanium material; depositing a first layer over and directly in contact with the germanium material of the substrate the first layer being a phosphorus-containing nucleation layer; depositing a second layer containing an arsenic dopant over the nucleation layer, the nucleation layer serving as a diffusion barrier to the arsenic dopant such that diffusion of the arsenic dopant into the germanium material of the substrate is limited in depth by the nucleation layer, wherein phosphorus material contained in the nucleation layer serves as a source of a dopant that forms a n-p junction in the germanium material of the substrate and wherein a two-step diffusion profile of arsenic and phosphorus forms a diffusion region in the germanium material of the substrate resulting in a shallow n-p junction in the substrate, and wherein an upper portion of the diffusion region has a higher concentration of phosphorus atoms than arsenic atoms, and a lower portion of the diffusion region has a higher concentration of arsenic atoms than phosphorus atoms; and depositing a sequence of layers over the second layer forming at least one solar subcell.