Heavily nitrogen-doped III-V semiconductors for high-efficiency solar cells

The authors demonstrate that the formation of an impurity band of the nitrogen-induced pair-bound states in GaAs_1-xN_x is responsible for the observed large band gap reduction, δE_g. δE_g is found to scale as x^2/3 (i.e., inversely proportional to the average separation of nitrogen pair centers). This is the same mechanism for the band gap reduction occurring in a heavily n-type or p-type doped semiconductor, where δE_g has been known to scale as x ^1/3 (i.e, inversely proportional to the average separation of the isolated impurity center). The nature of the impurity band leads to the intrinsically low carrier mobility in this material. Quantum confinement for the electron belonging to the impurity band has been demonstrated in GaAsN/GaAs quantum wells. The electron effective mass is found to decrease on increasing x, as expected for an impurity band