NachhaltigF: Elektrotechnik und MedientechnikI: IQMA
Y. Ji, H. Fei, Y. Shi, V. Iglesias, D. Lewis, N. Jiebin, S. Long, M. Liu, Alexander Hofer, Werner Frammelsberger, Günther Benstetter, A. Scheuermann, P. McIntyre, M. Lanza
Characterization of the photocurrents generated by the laser of atomic force microscopes
Review of Scientific Instruments, vol. 87, no. 8
The conductive atomic force microscope (CAFM) has become an essential tool for the nanoscale electronic characterization of many materials and devices. When studying photoactive samples, the laser used by the CAFM to detect the deflection of the cantilever can generate photocurrents that perturb the current signals collected, leading to unreliable characterization. In metal-coated semiconductor samples, this problem is further aggravated, and large currents above the nanometer range can be observed even without the application of any bias. Here we present the first characterization of the photocurrents introduced by the laser of the CAFM, and we quantify the amount of light arriving to the surface of the sample. The mechanisms for current collection when placing the CAFM tip on metal-coated photoactive samples are also analyzed in-depth. Finally, we successfully avoided the laser-induced perturbations using a two pass technique: the first scan collects the topography (laser ON) and the second collects the current (laser OFF). We also demonstrate that CAFMs without a laser (using a tuning fork for detecting the deflection of the tip) do not have this problem.
F: Elektrotechnik und MedientechnikI: IQMA
V. Iglesias, M. Lanza, K. Zhang, A. Bayerl, M. Porti, M. Nafría, X. Aymerich, Günther Benstetter, Z. Shen, G. Bersuker
Degradation of polycrystalline HfO2 based gate dielectrics under nanoscale electrical stress
Applied Physics Letters, vol. 99
The evolution of the electrical properties of HfO2/SiO2/Si dielectric stacks under electrical stress has been investigated using atomic force microscope-based techniques. The current through the grain boundaries (GBs), which is found to be higher than thorough the grains, is correlated to a higher density of positively charged defects at the GBs. Electrical stress produces different degradation kinetics in the grains and GBs, with a much shorter time to breakdown in the latter, indicating that GBs facilitate dielectric breakdown in high-k gate stacks.