| AVS 55th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoA |
| Session: | ALD: Functionalization and Surface Chemistry |
| Presenter: | J.J.H. Gielis, Eindhoven University of Technology, The Netherlands |
| Authors: | J.J.H. Gielis, Eindhoven University of Technology, The Netherlands B. Hoex, Eindhoven University of Technology, The Netherlands N.M. Terlinden, Eindhoven University of Technology, The Netherlands M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
Thin films of Al2O3 synthesized by (plasma-assisted) atomic layer deposition (ALD) provide an excellent level of surface passivation of c-Si and III-IV compound semiconductors, which is vital for the performance of devices such as nanocrystal or wafer-based light emitting diodes, photodetectors, and high-efficiency solar cells. Recently, it was demonstrated that the surface passivation properties of Al2O3 thin films arise after a postdeposition anneal.1 In general, surface passivation can be achieved by a reduction of surface defects or by electrostatic shielding of charge carriers by internal electric fields (i.e., field-effect passivation). In this contribution the nonlinear optical technique of second-harmonic generation (SHG) has been applied to study Al2O3 thin films on c-Si substrates with interfacial SiOx layers, both before and after anneal. SHG is a surface and interface specific technique that is extremely sensitive to internal electric fields. Spectroscopic SHG, carried out with a femtosecond Ti:sapphire laser tunable in the 2.66-3.50 eV SHG photon energy range, has revealed the presence of negative fixed charge in the Al2O3. For as-deposited Al2O3 films the negative fixed charge density was found to be on the order of 1011 cm-2, which increased to 1012-1013 cm-2 after anneal. The corresponding internal electric field most likely accounts for the surface passivation properties of Al2O3 thin films after anneal. The important role of the negative fixed charge density in the passivation properties of Al2O3 was confirmed by carrier lifetime spectroscopy and capacitance-voltage measurements. In addition, real-time SHG experiments causing multiple-photon-induced charge trapping suggest a reduction of recombination channels after anneal, which could play an additional role in the surface passivation mechanism by Al2O3. It is straightforward to extend the approach discussed in this contribution to enable contactless characterization of charge and charging dynamics in c-Si/high-κ dielectric structures in situ and during processing, which provides not only relevant information on field-effect passivation but also for nonvolatile memory and CMOS transistor applications.
1 B. Hoex et al. Appl. Phys. Lett. 89, 042112 (2006); Appl. Phys. Lett. 91, 112107 (2007).