Understanding and control of bipolar self-doping in copper nitride

• Published in: Journal of applied physics 2016-05, Vol.119 (18)
• Main Authors: Fioretti, Angela N., Schwartz, Craig P., Vinson, John, Nordlund, Dennis, Prendergast, David, Tamboli, Adele C., Caskey, Christopher M., Tuomisto, Filip, Linez, Florence, Christensen, Steven T., Toberer, Eric S., Lany, Stephan, Zakutayev, Andriy
• Format: Article
• Language: English
• Subjects: Applied physics; Combinatorial analysis; Copper; Defects; Doping; Electromagnetism; First principles; Hall effect; Nitrides; Positron annihilation; Seebeck effect; Semiconductor materials; Temperature; Temperature dependence; Temperature gradients; Thin films; X ray absorption
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4948244

Semiconductor materials that can be doped both n-type and p-type are desirable for diode-based applications and transistor technology. Copper nitride (Cu3N) is a metastable semiconductor with a solar-relevant bandgap that has been reported to exhibit bipolar doping behavior. However, deeper understanding and better control of the mechanism behind this behavior in Cu3N is currently lacking in the literature. In this work, we use combinatorial growth with a temperature gradient to demonstrate both conduction types of phase-pure, sputter-deposited Cu3N thin films. Room temperature Hall effect and Seebeck effect measurements show n-type Cu3N with 1017 electrons/cm3 for low growth temperature (≈35 °C) and p-type with 1015 holes/cm3–1016 holes/cm3 for elevated growth temperatures (50 °C–120 °C). Mobility for both types of Cu3N was ≈0.1 cm2/Vs–1 cm2/Vs. Additionally, temperature-dependent Hall effect measurements indicate that ionized defects are an important scattering mechanism in p-type films. By combining X-ray absorption spectroscopy and first-principles defect theory, we determined that VCu defects form preferentially in p-type Cu3N, while Cui defects form preferentially in n-type Cu3N, suggesting that Cu3N is a compensated semiconductor with conductivity type resulting from a balance between donor and acceptor defects. Based on these theoretical and experimental results, we propose a kinetic defect formation mechanism for bipolar doping in Cu3N that is also supported by positron annihilation experiments. Overall, the results of this work highlight the importance of kinetic processes in the defect physics of metastable materials and provide a framework that can be applied when considering the properties of such materials in general.