2004 Fiscal Year Final Research Report Summary
Studies on CdS diodes emitting light of various colors.
| Project/Area Number |
15360179
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electron device/Electronic equipment
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| Research Institution | Iwate University |
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Principal Investigator |
KASHIWABA Yasube Iwate Univ., Faculty of Eng., Prof., 工学部, 教授 (30003867)
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| Co-Investigator(Kenkyū-buntansha) |
BABA Mamoru Iwate University, Graduate School of Eng., Prof., 工学研究科, 教授 (20111239)
NISHIDATE Kazume Iwate University, Graduate School of Eng., Assoc.Prof., 工学研究科, 助教授 (90250638)
SATO Hiroaki Iwate University, Faculty of Eng., Assistant, 工学部, 助手 (90359498)
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| Project Period (FY) |
2003 – 2004
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| Keywords | LED / CdS / thin film / p-type / pn junction / photoluminescence / XPS / Cd-Zn-S |
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| Research Abstract |
The aims of this study were (1)to determine the role of Cu in Cu-doped CdS films, (2)to fabricate diodes emitting light of various colors using CdS thin films, and (3)to achieve de current operation of the diodes at room temperature. The following results were obtained.
1.Photoluminescences (PLs) of CdS : Cu and CdS films were measured to determine energy levels of Cu in CdS films. Excitonic emissions were observed in the PL spectra of CdS : Cu films. Shallow acceptor levels lower than 100 meV were also observed with deep acceptor levels. It is thought that these shallow acceptor levels show p-type characteristics on CdS : Cu films.
2.Light emissions from ITO/CdS : Cu/CdS/Al thin-film diodes were investigated under the condition of a forward pulse current at 77 K. Colors of emitted light changed depending on the current level : yellow to blue-green for samples with a low concentration of Cu and red to yellow for samples with a high concentration of Cu with increases in current density
It was shown that In in the ITO glass substrate of an ITO/CdS : Cu/CdS/Al thin-film diode diffused into CdS : Cu films and that it compensated the Cu acceptors in CdS : Cu films. An SnO_2-coated ITO (ITO/SnO_2) substrate prevented diffusion of In from ITO, and the use of an ITO/SnO_2 substrate enabled bright lights to be obtained.
3.Light emission from an ITO/SnO_2/CdS : Cu/CdS/Al thin-film diode was observed under the condition of de current at 77 K and room temperature. The colors changed depending on current density at 77 K, but the color was red at room temperature.
4.Mixed crystals of CdS and ZnS were also fabricated. Energy band gaps of the mixed crystals changed in the range of 2.4 to 2.8 eV depending on the ratio of ZnS to CdS. Cd_<1-x>Zn_xS : Cu films also showed p-type characteristics. Diodes using the films may emit blue and white lights.
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