Multicolor photoluminescence (PL) and electroluminescence (EL) were observed from newly developed Bi- and rare
earth (RE)-co-doped (La1-XGaX)2O3 ((La1-XGaX)2O3:Bi,RE) phosphor thin films. (La1-XGaX)2O3:Bi,RE phosphor thin
films were prepared by varying the Ga content (Ga/(La+Ga) atomic ratio) or the co-doped RE content (RE/(RE+La+Ga)
atomic ratio) under co-doping Bi at a constant content (Bi/(Bi+La+Ga) atomic ratio) of 3 at.% using a combinatorial r.f.
magnetron sputtering deposition method. High PL intensity was obtained in postannealed (La0.9Ga0.1)2O3:Bi,RE
phosphor thin films prepared with a Ga content around 10 at.%; TFEL devices fabricated using the phosphor thin films
exhibited high luminance. The obtained luminance intensities in EL and PL in the phosphor thin films prepared with
various contents of co-doped RE, such as Dy, Er, Eu, Tb and Tm changed considerably as the kind and content of RE
were varied. Color changes from blue and blue-green to various colors in PL and EL emissions, respectively, were
obtained in postannealed (La0.9Ga0.1)2O3:Bi,RE phosphor thin films, i.e., films prepared by co-doping Bi at a constant
content with various REs at varying levels of content. All the observed emission peaks in PL and EL from
(La0.9Ga0.1)2O3:Bi,RE phosphor thin films were assigned to either the broad emission originating from the transition in
Bi3+ or the visible emission peaks originating from the transition in the co-doped trivalent RE ion.
Reductions of the obtainable resistivity as well as improvements of the crystallinity in transparent conducting impuritydoped
ZnO thin films prepared on low-temperature glass substrates are demonstrated using a newly developed d.c. or r.f.
superimposed d.c. magnetron sputtering (dc-MS or rf+dc-MS) deposition technique. The improvements of the obtainable
lowest resistivity as well as the crystallinity in Al- and Ga-doped ZnO (AZO and GZO) thin films were achieved by
inserting a very thin buffer layer that was deposited using the same d.c. MS apparatus with the same target used to
deposit the AZO and GZO thin films. In addition, the insertion of the very thin buffer layer also improved the resulting
resistivity distribution on the substrate surface in AZO and GZO thin films. The buffer layer between the thin film and
the glass substrate was prepared by dc-MS or rf+dc-MS depositions using a target surface that was more strongly
oxidized than usually used during depositions conventionally optimized to obtain lower resistivity; the resulting thin
films could exhibit better crystallinity. A resistivity of approximately 3×10-4 Ωcm was obtained in 150-nm-thick-GZO
and -AZO thin films prepared on glass substrates at 200oC.
A new technique incorporating combinatorial deposition to develop new multicomponent oxide and oxynitride thin-film phosphors by r.f. magnetron sputtering is demonstrated using subdivided powder targets. By sputtering with a powder target that is subdivided into two or more parts, phosphor thin films with a chemical composition that varied across the substrate surface could be successfully prepared. In Zn2Si1-XGeXO4:Mn thin films, for example, the chemical composition (Ge content (X)) could be optimized to obtain higher electroluminescent and photoluminescent emission intensities by using only one deposition with the new technique. As a result, a high luminances of 11800 and 1536 cd/m2 for green emission was obtained in Zn2Si0.6Ge0.4O4:Mn TFEL device driven at 1 kHz and 60 Hz, respectively. In ((AlN)1-X-(CaO)X):Eu thin films, for example, the chemical composition (CaO content (X)) could be optimized to obtain higher electroluminescent and photoluminescent emission intensities by using only one deposition with the new technique. As a result, a luminance of 170 cd/m2 for red emission was obtained in an ((AlN)0.1-(CaO)0.9):Eu TFEL device driven at 1 kHz.
The effect of a buffer layer and/or interface region on the photovoltaic properties of Al-doped ZnO (AZO)/Cu2O heterojunction solar cells was investigated. The I-V characteristics and photovoltaic properties in AZO/ZnO-In2O3/Cu2O devices were considerably improved by increasing the Zn content (Zn/(In+Zn atomic ratio)) of the ZnO-In2O3 thin-film buffer layer. In addition, the photovoltaic properties of AZO/Zn1-XMgXO/Cu2O devices were found to degrade significantly as the composition (X) was increased above approximately 0.1 because of the increase in resistivity of the buffer layer. Although the spectral response of photocurrent observed in AZO/Zn1-XMgXO/Cu2O devices was considerably affected by altering the value of X, the photo-generated hole in the buffer layer of these devices was not successfully injected into the Cu2O. AZO/Cu2O heterojunctions fabricated using Cu2O sheets with a sulfurized surface exhibited ohmic I-V characteristics.
This article introduces newly developed multicomponent oxide host materials for electroluminescent phosphors. These are composed of Y2O3 and another binary compound such as Al2O3, Ga2O3, Gd2O3, In2O3, B2O3 or GeO2. The various Mn-activated (Y2O3)1-x-(oxide)x phosphor thin films were deposited while varying the composition by r.f. magnetron sputtering and postannealed. The obtained electroluminescent and photoluminescent emissions from the [(Y2O3)1-x-(oxide)x]:Mn phosphor thin-film emitting layers were strongly dependent on the preparation and postannealing conditions as well as on the composition. The highest luminance and photoluminescent intensity were obtained by using a (Y2O3)1-x-(oxide)x:Mn thin-film emitting layer prepared with an optimized composition. Both the obtained electroluminescent and photoluminescent characteristics were correlated to the crystallinity of the thin-film emitting layers. High luminances above 7000 cd/m2 were obtained in [(Y2O3)0.6-(GeO2)0.4]:Mn and [(Y2O3)0.5-(Ga2O3)0.5]:Mn thin-film electroluminescent devices fabricated under optimal condition and driven by an ac sinusoidal wave voltage at 1 kHz.
This paper describes the fabrication of pn heterojunction thin-film diodes using polycrystalline oxide semiconducting thin films. Al-oped ZnO (AZO) and Mg-doped CuCrO2 (CuCrO2:Mg) thin films used as n- and p-type oxide semiconducting layers, respectively, were prepared on glass substrates by r.f. magnetron sputtering using a powder target. The resulting p-type CuCrO2:Mg thin films prepared with a Mg content of 7 at.% exhibited at resistivity as low as 1.3x10-2Ωcm and a band-gap energy of 3.3 eV. The voltage-current (V-I) characteristic of a pn junction fabricated using p+-CuCrO2:Mg and n+-AZO thin films exhibited an ohmic, or linear, relationship. In addition, a pin heterojunction diode was fabricated by depositing high resistivity undoped ZnO and CuCrO2 thin-film layers, or i-layers, between the n+ -AZO and the p+-CuCrO2:Mg thin-film layers. The resulting p+-CuCrO2:Mg/i-CuCrO2/i-ZnO/n+-AZO thin-film pin junction diode exhibited a rectifying V-I characteristic and a photovoltage under UV light illumination.
High-luminance EL emissions were found to be obtainable using newly developed Mn-activated Y2O3-based multicomponent oxide phosphors composed of Y2O3 in combination with another binary compound, B2O3, Al2O3, Ga2O3, In2O3, Gd2O3, GeO2 or SiO2. The EL characteristics were investigated using a thick ceramic sheet-insulating-layer-type TFEL device. The Mn-activated Y2O3-based phosphor thin films were deposited by rf magnetron sputtering and postannealed. Luminances above 1000 cd/m2 were obtained in TFEL devices fabricated using a ((Y2O3)X-(Ga2O3)1-X):Mn, a ((Y2O3)X-(Gd2O3)1-X):Mn, a ((Y2O3)X-(Al2O3)1-X):Mn or a ((Y2O3)X-(GeO2)1-X):Mn thin film prepared with various compositions (X) and driven at 1 kHz. In particular, high luminances above 7000 cd/m2 for yellow emission were obtained in 1 kHz-driven TFEL devices using a ((Y2O3)0.6-(GeO2)0.4):Mn or a (Y2O3)0.5-(Ga2O3)0.5):Mn thin film prepared with a Y2O3 content of 60 or 50 mol.percent, respectively. In addition, high luminances above 500 cd/m2 and luminous efficiencies of approximately 10 lm/W were obtained in these TFEL devices driven at 60 Hz. High-luminance multicolor emissions that changed from yellow to green could be obtained in TFEL devices using a ((Y2O3)1-X-(Ga2O3)X):Mn thin film by increasing the Y2O3 content from 0 to 100 mol. percent.
KEYWORDS: Thin films, Gas sensors, Sensors, Chlorine, Thin film deposition, Chlorine gas, Temperature metrology, Glasses, Atmospheric sensing, Thin film devices
Chlorine (C12) gas sensors were newly developed using metal-phthalocyanines (MPc) such as CuPc, MgPc, ZnPc and FePc. All gas sensors using MPc thin films deposited by a vacuum evaporation method exhibited an increase in conductance with exposure to C12 gas at an operating temperature in the rage from 25 to approximately 200°C. The obtainable sensitivity of sensors was considerably affected by the MPc material used and the deposition conditions. The transient response of sensitivity was strongly dependent on the operating temperature of the MPc thin-film sensors. The increase in conductivity of the MPc thin films used in sensors that results from an increase in C12 gas concentration can be explained by the increase of carrier concentration dominating the effect of a decrease in Hall mobility. A high sensitivity as well as a fast response were realized for CuPc and MgPc thin-film sensors operated at approximately 200°C; C12 gas at a concentration of 0.18 ppm could be detected using these thin-film sensors operated in the range from 25 to 200°C.
Thick-insulating-ceramic-type thin-film electroluminescent (TFEL) devices with an oxide phosphor thin-film emitting layer have been fabricated by a sol-gel process that uses various source materials and eliminates the need for vacuum processes. The oxide phosphor thin-film emitting layer consisted of host materials such as Ga2O3, SnO2, ZnGa2O4 and (Ga2O3-Al2O3) multicomponent oxides activated with a transition metal element such as Mn and Cr or a rare earth element such as Eu. High luminances were obtained in TFEL devices with a Ga2O3:Mn, Ga2O3:Cr, SnO2:Eu, ZnGa2O4:Mn or (Ga2O3-Al2O3):Mn phosphor thin-film emitting layer. Luminances above 400 cd/m2 were obtained in green-emitting TFEL devices using Ga2O3:Mn thin films prepared by the sol-gel process, irrespective of source materials, when driven at 60 Hz. It was found that the EL characteristics of oxide phosphor TFEL devices improved as the driving frequency was increased from 60 Hz to 1 kHz. In a Mn- and Cr-co-doped Ga2O3 phosphor TFEL device, an emission color change from green to red as well as high luminances above 100 cd/m2 were obtained when driven at 10 kHz.
Cl2 and O3 gas detection at high sensitivity has been realized by newly developed thin-film gas sensors incorporating multicomponent oxides such as ZnO-In2O3, MgO-In2O3, and Zn2In2-MgIn2O4 systems. The sensors exhibited an increase in resistance with exposure to Cl2 or O3 gas. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the multicomponent oxide films used as well as the operating temperature. The highest sensitivity for Cl2 and O3 gases was obtained in sensors using a Zn2In2O5- MgIn2O4 thin film prepared with Zn2In2O5 contents of about 60 and 20 mol. percent respectively: Cl2 gas detected at a minimum concentration of 0.01 and O3 gas at 0.4ppm. A fast response as well as a high sensitivity were obtained in these sensors operated with alternating exposures in air and Cl2 or O3 gas. The resistivity, carrier concentration and Hall mobility of the thin-film sensors were measured under operation conditions using the van der Pauw method. It should be noted that a decrease or increase of resistivity in the thin-film sensors resulted from a simultaneously increase or decrease of both carrier concentration and Hall mobility. The increase in resistivity is attributed to the trapping of free electrons resulting from Cl2 and O3 being adsorbed on grain boundaries and/or the film surface, the same as that produced by adsorption of oxygen. A Zn2In2O5- MgIn2O4 thin-film gas sensor exhibited very stable long term operation in an atmosphere with a high concentration of Cl2 gas.
The possibility of practical thin-film electroluminescent (TFEL) displays using oxide phosphor emitting layers has been investigated with a single-insulating-layer device structure using a thick insulating ceramic sheet. Highluminance TFEL devices using rare earth- or transition metal-activated oxide phosphors consisting of binary, ternary and multicomponent oxide compounds are demonstrated. It is concluded that oxide phosphors are very promising as emitting layer materials for TFEL devices, because they can exhibit EL characteristics comparable with those of sulfide phosphors. It was found that various oxide phosphor TFEL devices can emit the three primary colors without the use of color filters. The emissions from the following highluminance oxide phosphor devices were found to be suitable for full-color displays: Ga2O:Mn, ZnGa2O4:Mn and Zn2SiO4:Mn for the green color and ZnGa2O4:Cr for the red color. In addition, a luminance of 592 cd/rn2 for yellow emission was obtained in a CaGa2O4:Mn TFEL device driven at 60 Hz. Keywords: Oxide Phosphor, Thin-Film Electroluminescent Device, Electroluminescence, Thin Film, Phosphor, Display, Flat Panel-Display, Oxide
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