2005 Fiscal Year Final Research Report Summary
Study of spin injection and its device application in ferromagnetic/semiconductor hybrid system
| Project/Area Number |
14076213
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | Japanese Advanced Institute of Science and Technology |
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Principal Investigator |
YAMADA Syoji Center for Nano Materoals and Technology, Prof, ナノマテリアルテクノロジーセンター, 教授 (00262593)
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| Co-Investigator(Kenkyū-buntansha) |
AKABORI Masashi Center for Nano Materoals and Technology, Assoc., ナノマテリアルテクノロジーセンター, 助手 (50345667)
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| Project Period (FY) |
2002 – 2005
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| Keywords | spin-orbit interaction / spin-injection / inverted heteroiunction / zero-field spin-splitting / narrow-gap semiconductor / spin transistor / side-gate / quantum computing device |
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| Research Abstract |
We have three major targets in this research project ; a) Development of novel narrow-gap heterojunction materials, b) Realization of high efficient spin-injection, c) Optimum design and device fabrication of Rashba type spin transistor. The main results obtained here are as follows ;
1) By adopting thick InAlSb buffer structure, we have succeeded to grow modulation-doped InGaSb/InAlSb (In content~0.9) hetero-junction on (001) GaAs substrates. Highest low temperature mobility is 1.2 x 10^5 cm^2/Vsec for sheet electron density of 3x10^11/cm^2, which is comparable to the record value so far obtained. The values of spin-orbit coupling constant are within 20-30 x 1042 eVm, which are similar to those obtained in high In-content InGaAs/InAlAs heterojunctions. In addition, from the detailed analysis of the Zeeman spin-splitting a under high magnetic fields, Dresselhaus contribution is found to be dominate even under low magnetic fields. This result contrasts to that in the InGaAs/InAlAs system
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not entirely expected previously. This is the result confirmed first time in our group, although the origin of this important and interesting phenomenon is not fully clear at present
2) As an example of important structure toward the Rashba-type spin-FM' realization, we have fabricated InGaAs/InAlAs narrow wires with the gates in the both sides. And investigated the effect of the side-gate voltage on the Rashba spin-orbit interaction in those wires. When the gate voltage is small, the effect of horizontal electric field due to the side-gates are confirmed, but it is replaced by the effect of vertical electric field when the gate voltages become large. That is, the value of the spin-orbit coupling constant takes a minimum when the two-gate voltages applied the each side-gate are balanced. But it increases monotonically when we increase the negative side-gate voltages further. This suggests the possibility of controlling the spin-orbit interaction by the side-gates as well as by the top-gates and could be developed to realize the Q-bit devices based on this type of spin-FET
3) We have developed high In-content inverted InGaAs/InAlAs heterojunction as a promising candidate of the material, in which high spin-injection could be realized with keeping high electron mobility as well as large spin-orbit coupling constant. The samples with thin (< 60 nm) surface InGaAs channel thickness are grown and the mobilities and the spin-orbit coupling constants similar to those in the same material normal type heterojunctions were confirmed. In the spin-injection experiments, reduced contact resistances of ferromagnetic electrodes attached on the heterijunction surface and reproducible spin-valve signals were successfully confirmed. Less
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