Nickel and iron—Multivalence impurities in GaP

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Abstract
Electron paramagnetic resonance and optical absorption measurements have been used to monitor the relative Ni0, Ni–, and Ni– – concentrations in various GaP samples with widely differing Fermi‐level positions. The data demonstrates that the two‐electron trap state Ni– – dominates in n‐type GaP, while Ni– and Ni0 are dominant in high‐resistivity p‐type material. Light‐induced valency changes with below band‐gap light were observed for all three charge states. The previously reported Fe– – level position is discussed in the light of the present Fe– – EPR data and the role of Ni and Fe as trapping centers in Zn‐diffused GaP light‐emitting diodes is emphasized.