| AVS 66th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Wednesday Sessions |
| Session EM+2D+AS+MI+MN+NS+TF-WeM |
| Session: | Nanostructures and Nanocharacterization of Electronic and Photonic Devices |
| Presenter: | Hantian Gao, Department of Physics, The Ohio State University |
| Authors: | H. Gao, Department of Physics, The Ohio State University M. Haseman, Department of Physics, The Ohio State University H. von Wenckstern, Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik M. Grundmann, Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik L.J. Brillson, The Ohio State University |
| Correspondent: | Click to Email |
Nanowires of the II-VI compound semiconductor ZnO have generated considerable interest for next generation opto- and microelectronics . Central to nanowire electronics is understanding and controlling native point defects, which can move1 and lead to dielectric breakdown under applied electric fields. We used nanoscale lateral and depth-resolved cathodoluminescence spectroscopy (DRCLS) with hyperspectral imaging (HSI) in a scanning electron microscope (SEM) to observe defect migration and redistribution directly under applied electric fields and after dielectric breakdown. HSI maps represent lateral intensity distributions of specific features acquired pixel by pixel across SEM-scanned areas and normalized to near band edge (NBE) emissions. A pulsed layer deposited (PLD) ZnO microwire (3 μm diameter) exhibited homogeneous distributions of common luminescence features at 2.0 eV (VZn cluster) and 2.35 eV (CuZn) as well as 2.7 and 2.9 eV (VZn) peaks near the wire surface. With increasing electrical bias up to 3x105 V/cm between two Pt contacts, these defects systematically redistribute, even at room temperature, moving toward and under one of the contacts, draining the “bulk” nanowire, especially its near-surface region. Since ionized VZn-related and CuZn antisite defects are acceptors, their removal reduces the compensation of electron density in the typically n-type ZnO and thus its resistivity.
Besides HSI lateral maps, DRCLS vs. incident beam energy yields depth profiles radially of defects at specific locations along the nanowire. These exhibit high near-surface and wire core densities that biasing reduces. Current voltage measurements with increasing field gradients show a gradual resistivity decrease until an abrupt dielectric breakdown of the microwire at 300 kV/cm (150 V/5 μm). The acceptor removal between the contacts and their accumulation under one of the contacts can both contribute to this breakdown due to the decrease in resistivity and higher current conduction between the contacts and possible defect-assisted tunneling2 across the increased defect density under the contact, respectively. These electric field-induced defect movements may be of more general significance in understanding dielectric breakdown mechanism not only in ZnO nanostructures but also bulk semiconductors in general.
HG, MH, and LJB gratefully acknowledge support from AFOSR Grant No. FA9550-18-1-0066 (A. Sayir). HVW and MG acknowledge Deutsche Forschungsgemeinschaft (Gr 1011/26- 1).
1. G. M. Foster, et al., Appl. Phys. Lett. 111, 101604 (2017).
2. J.W.Cox, et al., Nano Lett, 18, 6974 (2018).