An Amorphous IGZO Rare Earth Doped Luminescent Phosphor
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1111-D08-03
An Amorphous IGZO Rare Earth Doped Luminescent Phosphor Patrick Wellenius, Arun Suresh and John F. Muth Department of Electrical and Computer Engineering, NC State University, Raleigh, NC 27695 ABSTRACT Indium gallium zinc oxide (IGZO) has attracted recent attention as a high electron mobility amorphous material for high performance thin film transistors and subsequent use in active matrix backplanes for flexible displays. In this study, Eu:IGZO thin films were pulsed laser deposited at room temperature onto sapphire substrates and were investigated by cathodoluminescence and optical transmission. Photoluminescence was not observed with above band gap excitation at room temperature. Thin film electroluminescent (TFEL) devices were also fabricated from these thin films. These thin films and devices demonstrate characteristic europium emission, with the most intense emission at 611 nm corresponding to the 5D0 to 7F2 transition. Luminescence was observed to increase with increasing oxygen pressure during deposition of the Eu:IGZO thin films and may be related to the free carrier density in the films. The authors believe this to be the first report of an amorphous oxide thin film electroluminescent phosphor. INTRODUCTION Recent work on amorphous oxide semiconductors (AOS), particularly those based on the InxGayZn1-x-yOz (IGZO)1,2 system, has demonstrated this class of amorphous materials is capable of high carrier mobilities while being deposited and processed at room temperature. Comparisons to amorphous silicon suggest that amorphous IGZO holds promise as an optoelectronic material due to its wide bandgap and ionic structure. In this study, europium doped IGZO thin films have been deposited by pulsed laser deposition and subsequently characterized by cathodoluminescence and optical transmission. Furthermore, by fabricating thin film electroluminescent (AC-TFEL) devices from Eu:IGZO, we demonstrate a greater range of potential applications for this novel material system. We believe this is the first report of an AOS electroluminescent phosphor. IGZO is an n-type, high mobility, wide bandgap amorphous oxide semiconductor (AOS), first reported in 20042. IGZO and other AOS materials have been heavily researched for use as amorphous channels in transparent thin film transistors (TFTs) due to the ability to deposit and process these materials at or near room temperature. This capability makes IGZO compatible with commercially important polymer substrates such as polyethyleneterephtalate (PET), which begin to degrade at typical processing temperatures. Furthermore, the carrier density and mobility can be manipulated over a large range of values by changing the oxygen pressure during deposition3. This allows for fine tuning of channel properties in the fabrication of IGZObased enhancement or depletion mode transparent thin film transistors1. The relationship between oxygen pressure and conductivity is typically associated with the formation of n-type point defects in IGZO, such as oxygen vacancies or metal inters
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