Nitride Phosphors for Low Voltage Cathodoluminescence Devices
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Nitride Phosphors for Low Voltage Cathodoluminescence Devices
Hisashi Kanie, Takahiro Kawano, Kose Sugimoto, Ryoji Kawai Dept of Applied Electronics, Science Univ of Tokyo, Noda, Chiba, 278-8510, JAPAN.
ABSTRACT Undoped and Zn doped InGaN microcrystals were synthesized by a two-step method. The InGaN microcrystals have a wurtzite structure and brownish body color. The InGaN samples prepared at 900 °C did not contain a metal In phase. The InGaN:Zn microcrystals showed blue photoluminescence (PL) at 77K different from that of GaN:Zn. Reflectivity and photoluminescence excitation (PLE) measurement showed that the fundamental absorption edge of the InGaN:Zn phosphors is 3.47 eV, which implies that the In content in the InGaN:Zn phosphors is less than 0.2%. GaN:Zn and InGaN:Zn showed a Zn related PLE peak at 3.34 eV. InGaN and InGaN:Zn showed an In related PLE peak at 3.14 eV. When the InGaN:Zn samples were selectively excited at 3.15 eV, an In-related emission band centered at 2.2 eV emerged. The InGaN:Zn phosphors mounted on vacuum fluorescent displays (VFDs) showed room-temperature blue cathodoluminescence (CL) and the CL peak shifted slightly toward the low energy compared to that of the GaN:Zn phosphors because of the superimposed In related band. The InGaN:Zn phosphors had a luminance of 50 cd/m2 and a luminance efficiency of 0.03 lm/W at an anode voltage of 50 V.
INTRODUCTION GaN is a wide band gap semiconductor and has low resistivity, high luminescence efficiency, and chemical stability [1]. GaN:Zn or InGaN is used for an active layer in a highly efficient blue light emitting diode [1-4]. We synthesized microcrystaline GaN and InGaN by a reaction between the mixture of Ga2S3 and In2S3 and NH3 at 1050 °C [5-7] and reported that GaN:Zn microcrystals are applicable to phosphors for low-voltage CL devices, such as a field emission display (FED) or a VFD [5]. The current vs. anode voltage characteristics of VFDs using the GaN:Zn phosphors showed a threshold voltage as low as ZnO:Zn phosphors because of low resistivity of GaN. The CL spectra showed that a band in the violet region was dominant and a luminance efficiency in the blue region was not enough for practical use. To shift the emission band from the violet to the blue region and to increase the intensity
Q5.11.1
of emission band we prepared InGaN:Zn with better crystalline quality. Structural and optical properties of InGaN:Zn phosphors were studied. Structural properties of synthesized GaN, GaN:Zn and InGaN:Zn were measured using a conventional x-ray diffractometer. Low temperature PL and PLE spectra of InGaN:Zn phophors were recorded using a Xenon lamp. CL spectra and electric properties of InGaN:Zn phosphors mounted in VFDs were measure at room-temperature.
EXPERIMENTAL
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InGaN(21·3)
Si(53·1)
InGaN(10·5)
Si(51·1) InGaN(21·1) InGaN(11·4)
Si(42·2)
InGaN(20·3)
InGaN:Zn Nitridation Temperature 900 • InGaN(10·3) InGaN(20·0) InGaN(11·2) InGaN(20·1) Si(33·1) InGaN(20·2)
Si(31·1) InGaN(11·0)
Si(22·0) InGaN(10·2)
InGaN(10·1) In(101)
InGaN(10·0) In
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