| Budget Amount *help |
¥2,810,000 (Direct Cost: ¥2,600,000、Indirect Cost: ¥210,000)
Fiscal Year 2007: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2006: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Formation dynamics of electric field domains in semiconductor superlattices were investigated, and the following results were obtained.
1. Electric field domain formation in multiple finite-superlattice systems has been observed by photocurrent and photoluminescence measurements, and the experimental results supports the domain formation. Since the experimental current-voltage characteristics did not show any subband-resonance peaks, the electric field domain formation is novel phenomenon. We assumed a new mechanism originating Fowler-Nordheim tunneling for thick barriers separating the finite-superlattices, and performed a simulation. The simulated results agreed very well with the experimental results, and thus the mechanism was proved as novel origin of electric field domain formation in the multiple finite-superlattice structure. In addition, we have firstly be able to observe period by period movement of the domain boundary by photoluminescence measurement of the Stark-ladder trans
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ition in the finite-superlattices.
2. We found current oscillation originating from instability of electric field domain boundary in asymmetric multiple quantum well superlattices. Ordinarily, asymmetric multiple quantum well system does not show electric field domain formation. However, when a very thin barrier separates multiple asymmetric quantum wells, formation of electric field domain was observed experimentally. We have investigated this phenomenon by photoluminescence measurement, and found novel luminescence line which indicated spatially indirect hole transition. In addition, from our calculation, efficient electron wave function tunneling between a far separated quantum wells is supported due to very thin barrier. This resonance is the origin of the electric field domain formation in the asymmetric multiple quantum well superlattice. The evidence for this mechanism was supported by photoluminescence measurement from samples under electric field domain formation. The sample showed approximately 200 MHz current oscillation output. By using asymmetric multiple quantum well structures, allowance of structure design for electronic oscillators of semiconductor superlattice type will be extended more than the usual simple structured superlattices.
3. Investigation on higher energy subband states and the related carrier transports was performed, which may affect electric field domain formation. Less
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