摘要：

Cu 3 N layers with a thickness of 40 nm were depositedby reactive sputtering using Ar: 10% N 2 and 100% N 2 , after which they were annealed under NH 3 /H 2 between 300 and 500 °C. These exhibited distinct maximain differential transmission at 2.46, 2.30, 2.05, and 1.9eV on a picosecond time scale, as shown by ultrafast pump-probe spectroscopy.We show that the maxima at 1.9 and 2.05 eV correspond to the M andR direct energy band gaps of bulk Cu 3 N. In contrast, thehigher energy maxima at 2.46 and 2.30 eV are related to the occurrenceof strained Cu 3 N in the vicinity of the surface due tosurface oxidation upon exposure to the ambient. This is corroboratedby the fact that we observed a suppression of the high energy maximaat 2.46 and 2.30 eV by increasing the thickness of the Cu 3 N layers from 40 to 80 nm, which also rules out intervalley transfer.It is also consistent with the fact that we observed a suppressionof the low-energy peaks at 1.9 and 2.05 eV upon the intentional incorporationof oxygen during the deposition of Cu 3– x N 1– x O x . We describe these findings in conjunction with densityfunctional theory calculations of the electronic band structure ofCu 3 N and Cu 3– x N 1– x O x ,from which we find that oxygen is preferably incorporated as a shallowdonor without giving rise to midgap states and may be used to tailorthe direct energy band gaps of this defect-tolerant semiconductor,which in turn is important in the context of solar cells.

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