Amorphous semiconducting transparent oxides like InGaZnO4 (a-IGZO) have a broad distribution of metal and oxygen vacancy defects that determine thin film transistor (TFT) characteristics and impact device reliability metrics such as hysteresis. Here, we demonstrate how hydrogen modifies the density of states (DoS) through a novel on-chip method that spectrally resolves trap concentration in a-IGZO spanning the bandgap. Requiring laser energies continuously tunable from 0:26 to 3:1 eV, this method also employs difference frequency generation to access shallow states near the conduction band. We characterize the effect of hydrogen incorporation on the sub-gap peaks of the DoS of an a-IGZO TFT. Specifically, our data suggests hydrogen hybridizes with vacancy defects through metal-hydrogen (M-H) bonds that passivate oxygen vacancy sites and O-H bonds that passivate metal vacancy sites. These interactions result in a suppression of oxygen vacancy and metal vacancy- related trap states in the sub-gap and an enhancement of a metal-hydrogen bonding peak near the VBM. Temperature dependent, photon energy-dependent hysteresis, and transient defect lifetime measurements further reveal the strong impact of hydrogen concentration on a-IGZO TFT performance germane to current optical display technology.
John Wager, Melinda Valencia, Jeffrey Bender, Benjamin Norris, Hai Chiang, David Hong, Luke Norris, Taran Harman, Sangmoon Park, Jeremy Anderson, Cheol-Hee Park, Douglas Keszler, Janet Tate, Hiroshi Yanagi, Matthew Price, R. Hoffman
Transparent electronics is a nascent technology whose objective is
the realization of invisible electronic circuits. Part of the
impetus for the development of transparent electronics is the
recent availability of p-type transparent conductive oxides
(TCOs). With the emergence of p-type TCOs, in addition to
conventional n-type TCOs such as indium-tin oxide, tin oxide, and
zinc oxide, fabrication of transparent bipolar electronic devices
becomes feasible. The first part of this paper reviews TCOs and
discusses our work in the development of p-TCOs and alternative TC
materials (e.g. sulfides). We have recently invented a novel,
n-channel, accumulation-mode transparent thin-film transistor
(TTFT). This TTFT is highly transparent, has very little light
sensitivity, and exhibits electrical characteristics that appear
to be suitable for implementation as a transparent
select-transistor in each pixel of an active-matrix liquid-crystal
display (AMLCD). Moreover, the processing technology used to
fabricate this device is relatively simple and appears to be
compatible with inexpensive glass substrate technology. The second
part of this paper focuses on TTFTs. If transparent electronics is
employed to realize transparent back-plane electronic drivers on
transparent substrates, fabrication of a transparent display
becomes feasible. The third part of this paper offers an approach
for realization of a transparent display.
Photoluminescenc eand electroluminescence of CaSiN2:Eu materials were investigted to develop a new phosphor for thin film electroluminescence (TFEL) device applications. Ca3N2 and Si3N4 powders were mixed to form CaSiN2 hostmaterials and Eu was added as the luminescent center. The mixed powermatrials were cold pressed under the pressure of 1 Kg/cm2 to make pellets, and fired at 1400 degrees Celsius for 2 hours under N2H2 envrionemtn. Th ex-ry diffraction(CRD) patterns of synthesizd materals wer well matched with CaSiN2 of joint committee for powder diffraction standards (JCPDS) csrad. When illuminated by ultravilet rays, th enew phosphors emitted very bright red ligh of peak wav lenegth centered at 620 nm. Th TFEL devices with CaSiN2:Eu phosphor layser swre grown by sputter depositonof CaSiN2:Eu target. Red light emission was observed when the peak amplitude of the applied voltge exceeded 116 V.l The luminance was shown to increase sharply withth increase of the applied voltage. The maximum luminance was 1.62 Cd/m2 at the applied peak voltage of 276 V. The red emission from CaSiN2:Eu TFEL device seems to result from electronic transition of Eu3+ ions.The emission spectra of TFEl devices matchwell withth ephotoluminescence spectra of CaSiN2:Ey powders. The new devices structure and fabrication processes for the iimprovement of emission intenityof CaSiN2:Eu TFEl devices ar under investigation.
A new class of blue thin-film electroluminescent (TFEL) devices based on thiogallate phosphors has been reported recently. The purpose of this work reported herein is to compare and contrast the electrical properties of CaGa2S4:Ce TFEL blue phosphor devices to those of conventional evaporated ZnS:Mn TFEL devices. Capacitance-voltage (C-V) and internal charge-phosphor field (Q-Fp) techniques are employed for electrical characterization.
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