2003 Fiscal Year Final Research Report Summary
Step structure control of Molecular ciystals and Multiplication-type Photosensing devices
| Project/Area Number |
14550009
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | Osaka University |
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Principal Investigator |
HIRARNOTO Masahiro Osaka Univ., Grad.School.Eng, Associate Professor, 大学院・工学研究科, 助教授 (20208854)
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| Co-Investigator(Kenkyū-buntansha) |
YOKOYAMA Masaaki Osaka Univ., Grad.School.Eng., Professor, 大学院・工学研究科, 教授 (90029281)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Photocurrent Multiplication / Molecular Blind Alley / Molecular Crystals / Molecular Step / Kink Structure / Organic / Metal Interface / Structural Trap / Epitaxial Growth |
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| Research Abstract |
We have observed the large photocurrent multiplication phenomenon reaching 10^5-fold at metal/organic interface. Multiplication mechanism is the tunneling injection of electrons from metal electrode to organic layer triggered by the accumulation of photogenerated holes captured by the interfacial structural trap, namely, blind alleys at imperfect organic/metal contact which capture holes under the concentrated electric field toward metal.
Spatial gaps at metal/organic interface providing the hole capturing area, which is formed due to the partial contact of metal nanospheres to organic surface, were confirmed to exist.
Molecular steps on the organic crystal surface were revealed to act as blind alleys (molecular blind alley, MBA). As expected, single crystal surface having little molecular steps hardly showed multiplication. Moreover, multiplication rate increased with the number of MBA trap sites, i.e., the number of kinks in steps. Intentional fabrication of steps by epitaxial growth on the molecular-level flat crystal surface was confirmed to arise multiplication.
Both molecular blind alleys and spatial gaps are indispensable to cause photocurrent multiplication. Design of step structure at crystal surface would be an effective way to control the carrier injection to organic semiconductors.
High-speed photocurrent multiplication devices using co-deposited films of copper phthalocyanine and fullerene were fabricated. Photoresponse time for light on and off reached 3 and 15 ins, respectively, which were in striking contrast to those for single fullerene films requiring several seconds. Performance of the present device is promising for the application to multiplication-type photodetector.
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