New Transparent Magnetic Semiconductor Ni_xCu_1–xI which Can Perform as Either P-type or N-type and Success in the P–N Homojunction Diode

A semiconductor that can be doped to be either p-type or n-type is of great importance, as p–n homojunctions are desirable for realizing various electronic devices and processes. However, because of pervasive doping asymmetry for wide band gap semiconductors, the achievement of both p-type and n-type in a single wide gap material is very difficult. Here, we report the success in developing a new transparent magnetic NixCu1–xI halide semiconductor that can be either p-type or n-type depending on Ni fraction in NixCu1–xI. For 0 ≤ x ≤ 0.10, NixCu1–xI films show p-type conductivity. For the range 0.15 ≤ x ≤ 0.35, NixCu1–xI films show an n-type character. The NixCu1–xI films are electrically conducting and optically transparent and show soft ferromagnetic behavior with an optimum conductivity of 42 S cm–1 (x = 0.03) and visible light transmission of 80%. Ultraviolet photoelectron spectroscopy studies on NixCu1–xI films reveal the systematic Fermi level shift toward the conduction band with respect to the valence band as a function Ni concentration. X-ray photoelectron spectroscopy analysis on Ni and I peak positions reveals Ni+2 valence for Ni in NixCu1–xI films, with signatures of Ni–I bonding. The observed p-type behavior originates from Cu vacancy, while the n-type character is identified to originate from the electron donor states generated by Ni incorporation in NixCu1–xI. The constructed homojunction with p-Ni0.0Cu1.0I/n-Ni0.16Cu0.84I shows a characteristic p–n junction behavior with a good rectification ratio of 2 × 102. This new type of NixCu1–xI transparent semiconductor with a tunable carrier type and magnetism may be a candidate for halide-based optoelectronic as well as spintronics development.