Oxygen-Doped Zinc Nitride as a High-Mobility Nitride-Based Semiconductor

While many types of transparent conducting oxides (TCOs) have been developed, nitride-based transparent conductors remain rare. We examined the properties of zinc nitride doped with oxygen (Zn3N2-xOx) as a potential nitride-based transparent conductor. Electron density on the order of 10(20) cm(-3) was achieved by heavy oxygen doping. A minimal resistivity (rho) of 6.2 x 10(-4) Omega cm, comparable to those of TCOs, was observed for x = 0.19. Notably, the Zn3N1.81O0.19 films had high electron mobility of 85 cm(2) V-1 s(-1), 2-3 times larger than the values for TCOs. Detailed analyses of mobility revealed that the electron transport was governed by ionized impurity scattering, and the dominant scattering center was substitutional oxygen. The contributions of additional scattering mechanisms were relatively minor. These findings explain the high observed mobility in Zn3N2-xOx films. Contrary to our expectations, visible transmittance of Zn3N2-xOx films was below 40%. X-ray photoelectron spectrometry suggested the existence of self-interstitial nitrogen (N-I) in Zn3N2-xOx films. Low transmittance was attributable to optical absorption by electron transitions between the in-gap state originated from N-I bonded to lattice nitrogen (N-N) and the band states. These results suggest that, when the formation of N-N-N-I bond is suppressed, Zn3N2-xOx can be a high-mobility transparent conductor.