Probing the Nanoscale Interplay of Native Defects and Doping in Oxide Semiconductors

Nanoscale optical and electrostatic techniques can now directly measure the movement of native point defects inside oxide semiconductors and how they control space charge regions, tunneling, and contact rectification. Depth-resolved cathodoluminescence spectroscopy (DRCLS) with hyperspectral imaging measures 3-dimensional defect redistribution on a nanoscale for ZnO, Ga₂O₃, SrTiO_3, and BaSrTiO₃, revealing how intrinsic and applied electric fields drive defect movement. Defects at metal-ZnO diodes change carrier densities, tunneling, and trap-assisted hopping, altering Zn- vs. O-polar Schottky barriers. Native point defects are present inside, not only on the surfaces of ZnO nano- and microwires as commonly thought.^1,2 Nanoscale 3D measurement and imaging reveal electrically-active defects that extend deep inside wires, introducing new donors or acceptors that alter depletion widths, conducting channel volumes, and metal-ZnO nano-contact rectification. Using electron and ion beams, we altered defect distributions to create rectifying, ohmic, or blocking contacts with the same metal on the same nanowire, demonstrating the interplay between the nature of native point defects, the intrinsic doping, and the physical dimensions of the nanostructure itself in determining the electronic properties of the oxide interface.³ DRCLS also enabled us to correlate the dominant luminescence features of Ga₂O₃ with the most thermodynamically stable O vacancy, Ga vacancy, and Ga vacancy-hydrogen defect states in the band gap predicted theoretically.⁴ As with ZnO, the combined depth-resolved detection and processing of Ga₂O₃ suggests new avenues for identifying and controlling native point defects in semiconductors.
1. W. Ruane et al., Nanoscale 8, 7631 (2016).
2. A. Jarjour et al., Ann. Phys. (Berlin) 530, 1700335 (2018).
3. J. Cox et al., Nano Lett. 18, 6974 (2018).
4. H. Gao et al., Appl. Phys. Lett. 112, 242102 (2018).