C Team - Transparent Oxides

Key Publications

  • Yu, X. G.; Marks, T. J.; Facchetti, A., Metal oxides for optoelectronic applications. Nat. Mater. 2016, 15 (4), 383-396.

  • Wang, B. H.; Zeng, L.; Huang, W.; Melkonyan, F. S.; Sheets, W. C.; Chi, L. F.; Bedzyk, M. J.; Marks, T. J.; Facchetti, A., Carbohydrate-Assisted Combustion Synthesis To Realize High-Performance Oxide Transistors. J. Am. Chem. Soc. 2016, 138 (22), 7067-7074.

  • Huang, W.; Zeng, L.; Yu, X. G.; Guo, P. J.; Wang, B. H.; Ma, Q.; Chang, R. P. H.; Yu, J. S.; Bedzyk, M. J.; Marks, T. J.; Facchetti, A., Metal Oxide Transistors via Polyethylenimine Doping of the Channel Layer: Interplay of Doping, Microstructure, and Charge Transport. Adv. Funct. Mater. 2016, 26 (34), 6179-6187.

  • Yu, X.; Smith, J.; Zhou, N. J.; Zeng, L.; Guo, P. J.; Xia, Y.; Alvarez, A.; Aghion, S.; Lin, H.; Yu, J. S.; Chang, R. P. H.; Bedzyk, M. J.; Ferragut, R.; Marks, T. J.; Facchetti, A., Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors. Proc. Natl. Acad. Sci. USA 2015, 112 (11), 3217-3222.

  • Hennek, J. W.; Kim, M.-G.; Kanatzidis, M. G.; Facchetti, A.; Marks, T. J., Exploratory Combustion Synthesis: Amorphous Indium Yttrium Oxide for Thin-Film Transistors. J. Am. Chem. Soc. 2012, 134 (23), 9593-9596.

  • Kim, M.-G.; Kanatzidis, M. G.; Facchetti, A.; Marks, T. J., Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing. Nat. Mater. 2011, 10 (5), 382-388.

Transparent Oxide Thin Film Deposition

Metal-Organic Chemical Vapor Deposition (MOCVD)
C-team research in MOCVD is two-fold. First, we develop new molecular metal-organic precursors targeted for thin film growth by metal-organic chemical vapor deposition (MOCVD). These precursors must be volatile, low-melting, monomeric complexes of the metals desired. Additional desirable characteristics for potential MOCVD precursors include thermal stability, non-toxicity, and a high-temperature decomposition pathway that leads to zero ligand incorporation into the growing film at the heated substrate interface. Synthesis of these main group, transition metal, and lanthanide complexes requires versatile skills, from air-free Schlenk and glovebox techniques to strategic organic synthetic applications.



Figure 1. ORTEP drawing of Cd precursor, Cd(hfa) 2(N,N’-DE-N,N’-DMEDA)

The second component of our research is identifying metal oxide films of interest to the materials science community, and demonstrating in-house the MOCVD growth of these films using the precursors developed in our laboratory. MOCVD is often the preferred industrial method for thin film growth (it is used heavily in the semiconductor industry), but is limited by the availability of suitable precursors. The work our group carries out therefore makes a strong contribution to the field.



Figure 2. Cross-sectional TEM and SAED images of MOCVD-CdO films grown on glass (top) and MgO(100) (bottom)

Ion-Assisted Deposition (IAD)

Ion-Assisted Deposition (IAD) is a scalable process combining two active ion beams to simultaneously manipulate film growth, oxidation, and crystallization. Besides the background O2 partial pressure, additional O2 can be integrated into the assisted ion beam to produce active oxygen ions. High-quality transparent oxide films, including conductors, semiconductors, and insulators, can be deposited with this technique, even on organic or plastic substrates at room temperature. Our research focuses on novel oxide films for electronic device applications, as well as the film growth mechanisms.



Figure 3. AFM images of IAD-ITO at thicknesses of 2, 4, 17, 40, 90, and 150nm from (a) to (f)

Thin Film Applications in Electronic Devices

Transparent Conducting Oxide (TCO)
Because of the soaring In price and the modest conductivity of ITO, novel transparent conducting oxide (TCO) thin films with greater conductivity but lower cost are highly desired in optoelectronic devices, including light-emitting diodes (LEDs), photovoltaics (PVs), and eletro-optical (EO) modulators.


Figure 4. Cross-sectional TEM image of an EO modulator using MOCVD-ZnO and IAD-In2O3 as electrodes



Figure 5. Cross-sectional TEM image of a highly-conductive In-doped CdO/ITO bilayer

Transparent Oxide Semiconductor (TOS) & Transparent Oxide Insulator (TOI)
Both semiconductor and insulator are important components of thin film transistors (TFTs). Flexibility, transparency, light weight, low power consumption, and low operating voltage are among the most desirable characteristics for producing switching units in portable devices. We develop TOS films with high field mobility and TOI with high dielectric constant and good insulating properties to realize flexible transparent TFTs with low operation voltage and low power consumption.



Figure 6. Full transparent TFTs using IAD-In2O3 TOS channels with high mobility of ~120 cm^2/V•s at 1V

Collaborations
The C-team also actively contributes to many collaborating projects. We cooperate with material scientists, theorists, physicists, and electrical engineers from Northwestern, Purdue, UCLA, and BP Solar on numerous projects.



Figure 7. Conducting AFM image of transparent conductive pattern “NU TCO” written with Ga FIB in IAD-In2O3



Figure 8. Active Matrix OLED display driven by In2O3 nanowire transistor

Recent Publications

Recent Journal Covers

Inorganic Chemistry, October 7, 2002
Chemistry of Materials, January 10, 2006


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