Andrew W. Metz

Indium-cadmium-oxide films having exceptional electrical conductivity and optical transparency: Clues for optimizing transparent conductors

Materials with high electrical conductivity and optical transparency are needed for future flat panel display, solar energy, and other opto-electronic technologies. InxCd1-xO films having a simple cubic microstructure have been grown on amorphous glass substrates by a straightforward chemical vapor deposition process. The x = 0.05 film conductivity of 17,000 S/cm, carrier mobility of 70 cm2/Vs, and visible region optical transparency window considerably exceed the corresponding parameters for commercial indium-tin oxide. Ab initio electronic structure calculations reveal small conduction electron effective masses, a dramatic shift of the CdO band gap with doping, and a conduction band hybridization gap caused by extensive Cd 5s + In 5s mixing.

First-principles calculations for understanding high conductivity and optical transparency in InxCd1−xO films

Abstract We investigate In x Cd 1− x O materials, where x =0.0, 0.031, 0.063 and 0.125, to understand their high electrical conductivity and optical transparency windows, using the full-potential linearized augmented plane wave (FLAPW) method. In addition, we employ the screened exchange LDA (sX-LDA) method to evaluate accurate band structures including band gap that is underestimated by the LDA calculations. The results show a dramatic Burstein–Moss shift of the absorption edge by the In doping, reflecting the small effective mass of the Cd 5s conduction band. The calculated direct band gaps, 2.36 eV for x =0.0 and 3.17 eV for x =0.063, show excellent agreement with experiment. The effective mass of the conduction band of CdO is calculated to be 0.24 m e (in the ▵ direction), in good agreement with an experimental value of 0.27m e , explaining its high electrical conductivity. The hybridization between the Cd 5s and the In 5s states yields complex many-body effects in the conduction bands: a hybridization gap in the conduction bands and a band-gap narrowing which cancels the further Burstein–Moss shift for higher In doping.

Development and Implementation of New Volatile Cd and Zn Precursors for the Growth of Transparent Conducting Oxide Thin Films Via Mocvd

For the growth of thin zinc group metal oxide films [i.e. cadmium oxide (CdO), cadmium stannate (Cd 2 SnO 4 ), and zinc oxide (ZnO)] via metal-organic chemical vapor deposition (MOCVD), volatile Cd and Zn precursor families are needed. Starting with Cd, β-ketoiminates of varying substitution were prepared to elucidate structure-property relationships. The nature of the ligand substituents strongly influences the melting point (liquid precursors are desired). Unlike conventional Cd β-diketonates, these complexes are monomeric as determined by x-ray crystallography. Despite these advantageous characteristics, attempts to grow CdO thin films in a cold-wall MOCVD reactor using two such derivatives were not successful. This class of Cd complex appears to decompose thermally with time-- a likely cause of the poor performance. Therefore, a new series of more thermally stable Cd precursors was sought. Using the chelating diamine N,N,N 1 ,N 1 -tetramethylethylenediamine (TMEDA), monomeric β-diketonates were prepared. The molecular structure of Cd(hfa) 2 (TMEDA) (hfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) confirms the monomeric structural assignment. This series of Cd complexes is appreciably more volatile and sublime more cleanly than the aforementioned β-ketoiminates, as determined by vacuum thermogravimetric analysis (TGA). In addition to this advantageous characteristic, these complexes are easily prepared under ambient laboratory conditions from commercially available starting materials in a single step. Following the protocol established for Cd, a volatile series of Zn precursors was also prepared. For the Zn series, the melting point was effectively tuned through variation of both the β-diketonate and diamine ligands. The use of the Cd and Zn β-diketonate precursors in the successful growth of CdO and ZnO thin films, respectively, by MOCVD is also presented.

Highly transparent and conductive CdO thin films as anodes for organic light-emitting diodes: Film microstructure and morphology effects on performance

— Highly conductive and transparent CdO thin films have been grown on glass and on single-crystal MgO(100) by MOCVD at 400°C and were used as transparent anodes for fabricating small-molecule organic-light emitting diodes (OLEDs). Device response and applications potential have been investigated and compared with those of control devices based on commercial ITO anodes. It is demonstrated that highly conductive CdO thin films of proper morphology can efficiently inject holes into such devices, rendering them promising anode materials for OLEDs. Importantly, this work also suggests the feasibility of employing other CdO-based TCOs as anodes for high-performance OLEDs.

Highly Transparent and Conductive CdO Thin Films as Anodes for Organic Light-Emitting Diodes

In this paper, CdO thin films are used for the first time as transparent anodes for organic light-emitting diodes (OLEDs). Highly conductive and transparent CdO thin films have been grown on glass and on single-crystal MgO(100) by low pressure metal-organic chemical vapor deposition (MOCVD) at 400°C, and were implemented in small-molecule OLED fabrication. Device response and applications potential have been investigated and compared with those of commercial ITO-based control devices. It is found that as-deposited CdO thin films are capable of injecting holes into such devices, rendering them promising anode materials for OLEDs. A maximum luminance of 32,000 cd/m 2 and an external forward quantum efficiency of 1.4 %, with a turn-on voltage of 3.2 V are achieved on MgO(100)/CdO-based devices.

New Low-melting Cadmium Precursors for the Detailed Study of Texture Effects in MOCVD Derived CdO Thin-Films

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Volatile, Fluorine-Free β-Ketoiminate Precursors for MOCVD Growth of Lanthanide Oxide Thin Films

Lanthanide oxide thin films are of increasing scientific and technological interest to the materials science community. A new class of fluorine-free, volatile, low-melting lanthanide precursors for the metal-organic chemical vapor deposition (MOCVD) of these films has been developed. Initial results from a full synthetic study of these lanthanide-organic complexes are detailed.