| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF+AS+EL+EM+NS+PS+SS-ThA |
| Session: | IoT Session: Thin Films for Flexible Electronics and IoT |
| Presenter: | Erwin Kessels, Eindhoven University of Technology, The Netherlands |
| Authors: | Y. Wu, Eindhoven University of Technology, The Netherlands B. Macco, Eindhoven University of Technology, The Netherlands A.D. Giddings, CAMECA Instruments Inc. T.J. Prosa, CAMECA Instruments Inc. D.J. Larson, CAMECA Instruments Inc. S. Kölling, Eindhoven University of Technology, The Netherlands P.M. Koenraad, Eindhoven University of Technology, The Netherlands F. Roozeboom, Eindhoven University of Technology, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands M.A. Verheijen, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
Transparent conductive oxides (TCOs) are ubiquitous in many of today’s electronic devices, including solar cells. Atomic layer deposition (ALD) is a promising method to prepare high quality TCO films due to its well-known virtues – i.e., precise growth control, excellent conformality and uniformity – combined with its damage-free character. Here we report on two types of TCO films that we have studied by a combination of atom probe tomography (APT) and high-resolution transmission electron microscopy (TEM). The aim was to get more insight into how the dopants are distributed in the films.
The first study was carried out on ZnO:Al prepared by alternating cycles of Zn(C2H5)2 and H2O with cycles of Al(CH3)3 and H2O in a supercycle fashion at 250 ⁰C. For this material it is known that the maximum conductivity achievable is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the 3-dimensional distribution of Al atoms in the ZnO host material matrix has been examined at the atomic scale by the aforementioned techniques [1]. Although the Al distribution in ZnO films prepared by so-called “ALD supercycles” is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers was observed with a full-width-half-maximum of ~2 nm. In addition, an enrichment of the Al at grain boundaries was seen.
The second study involved In2O3:H prepared by InCp and a mixture of O2 and H2O at 100 ⁰C. This material provides a record optoelectronic quality after post-deposition crystallization of the films at 200 ⁰C. Since both the H dopant incorporation and the film microstructure play a key role in determining the optoelectronic properties, both the crystal growth and the incorporation of H during this ALD process were studied [2]. TEM studies show that an amorphous-to-crystalline phase transition o ccurs in the low temperature regime (100-150 °C), which is accompanied by a strong decrease in carrier density and an increase in carrier mobility. Isotope studies using APT on films grown with D2O show that the incorporated hydrogen mainly originates from the co-reactant and not from the InCp precursor. In addition, it was established that the incorporation of hydrogen decreased from ~4 at. % for amorphous films to ~2 at. % after the transition to crystalline films.
[1] Y. Wu, A. Giddings, M.A. Verheijen, B. Macco, T.J. Prosa, D.J. Larson, F. Roozeboom, and W.M.M. Kessels, Chem. Mater. 30, 1209 (2018).
[2] Y. Wu, B. Macco, D. Vanhemel, S. Kölling, M.A. Verheijen, P.M. Koenraad, W.M.M. Kessels, and F. Roozeboom, ACS Appl. Mater. Interfaces, 9, 592 (2017).