| AVS 54th International Symposium | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS-TuM |
| Session: | Imaging of Nanostructures |
| Presenter: | A.A. Baski, Virginia Commonwealth University |
| Authors: | J.C. Moore, Virginia Commonwealth University M.A. Reshchikov, Virginia Commonwealth University J. Xie, Virginia Commonwealth University H. Morkoc, Virginia Commonwealth University A.A. Baski, Virginia Commonwealth University |
| Correspondent: | Click to Email |
A new combination of conducting atomic force microscopy (CAFM) and scanning Kelvin probe microscopy (SKPM) was used to study localized charge trapping for MBE-grown GaN films. Charge was injected into the near-surface region of a GaN film by scanning local regions using CAFM with a reverse bias applied to the sample. Time-resolved local surface potential measurements were then obtained using SKPM after charge injection, where an induced band bending caused by charging of surface/interface states was observed. In dark environments and for applied CAFM biases greater than 10 V, the density of charged states (2x1012 cm-2) doubled immediately after scanning as compared to unscanned regions. This increase in charged states resulted in an increase of surface band bending of ~3 eV that dissipated quasi-exponentially with time. Induced band bending greater than 0.5 eV was still observed up to 4 hr after charge injection, indicating that charge trapping is relatively stable in a dark environment. Initial values for band bending depend on the applied CAFM bias during injection, where nominal band bending (<0.5 eV) occurs for biases less than 8 V and a saturation value of ~3 eV occurs at biases greater than 10 V. A phenomenological model was used to model the CAFM charge injection via a tunneling mechanism, where electrons travel from the tip through a thin surface gallium oxide barrier and become trapped at the oxide/GaN interface. Saturation occurs due to the existence of a finite density of chargeable interface states. After charging occurs via CAFM, the decrease in induced band bending with time was found to be consistent with a thermionic model of charge transfer from the interface to the bulk. As expected, charged interface states could be rapidly neutralized (<1 s) via photovoltage caused by illumination with UV light. Funding provided by NSF and AFOSR.