Good bulk transport Poor interfacial transport Cu Reactive O Magnetron Sputtering: O2 gas flow h+ Jonas Deuermeier, PhD. Student h+ > 200 nm Cu2O Supervisors: Prof. Elvira Fortunato (UNL) Prof. Andreas Klein (TUD) ~ 12 nm Cu2O Defects at interface Objectives What is responsible for limited device Electronic defects? Diffusion? performance of p-type oxide TFTs? Where in the device? How can we measure this? Electrical characterization? X-ray and ultraviolet Photoelectron Spectroscopy Photoelectron Spectroscopy on interface? Can we overcome the limitations? Mechanisms intrinsic to the material? Complications induced by fabrication? What can we do to improve devices? Alternative combination of materials? New device structures? … ? chambers: Magnetron Atomic Layer Deposition Figure 1 Photolithography Devices Cu(0) 0.3-0.4 In situ X-ray and Ultraviolet Transport properties Photoelectron Spectroscopy (fig. 1) Comparison of bulk and thin film Cu2O EF 0.5 EF 0.2 0.3-0.4 2.8 Cu2O 4.5 *General characterization of material: X-ray diffraction, Scanning Electron Microscopy, Hall-Effect, UV-Vis-NIR Spectroscopy, ... EVBM Results [eV] Magnetron Sputtering More oxidized state (y>0) → more intrinsic acceptors VCu → higher hole concentration Al2O3 by [1] Atomic Layer Deposition → Keep Cu2O stoichiometric, even down to the interface level Top-gate geometry: Clear chemical damage to Cu2O channel by Al2O3 deposition Al2O3 by EVBM Non-stoichiometric Cu2-yO: • Cu(II) Cu2O Chemical analysis and energy band alignment of substrate and film e- hn [2] Figure 2 (fig. 2) Al2O3 by Atomic Layer Deposition → reduction to Cu(0), Schottky-barrier formation 0 • Al2O3 by reactive Magnetron Sputtering → oxidation to Cu(II), lower Fermi energy -2 • High Hall mobility (32 cm2/Vs) but low field-effect mobilty and on-off ratio in TFT (fig. 3) • In situ XPS: Cu(II) in Cu2O changes with increasing film thickness (fig. 4) • In progress: Temperature- and time-dependent electrical measurements of bulk Cu2O and TFTs -4 -6 0.4 VD= -1V W/L= 40/20 0.0 -10 -45 -30 -15 0 15 30 VG (V) -8 0 -100 VG 6 steps 30 to -45 V -200 2 Bottom-gate geometry: Evidence for defective growth of Cu2O on dielectric 0.8 -3 → No working transistor devices 1.2 fe (10 cm /VS) • ID (nA) Atomic Layer Deposition: gate dielectric Al2O3 UHV Sputtering, Methods and techniques Reactive Magnetron Sputtering: p-type Cu2O* Preparation ID (nA) -300 -40 -20 VD ( V) Publications [2] Deuermeier, J., Yanagi, H., Bayer, T. J. M., Martins, R., Klein, A., and Fortunato, E., Advanced Materials Interfaces (submitted) Figueiredo, V. , Pinto, J. V., Deuermeier, J., Barros, R., Alves, E., Martins, R., and Fortunato, E., J. Disp. Technol. 9, 735–740 (2013). Bayer, T. J. M., Wachau, A., Fuchs, A., Deuermeier, J., and Klein, A., Chem. Mater. 24, 4503– 4510 (2012). [1] Deuermeier, J., Gassmann, J., Brötz, J., and Klein, A., J. Appl. Phys. 109, 113704 (2011). 0 Figure 3 to tackle questions on defect mechanisms 0.05 Cu(II) in Cu2O (%) CENIMAT – Materials Research Centre, New University of Lisbon Transparent p-type transistors based on Cu2O – Understanding material properties to enhance device performance Cu/O: 1.98 1.91 2.05 2.05 2.11 0.04 0.03 0.02 0.01 0.00 1 10 thickness (nm) 100 Figure 4