2007 Fiscal Year Final Research Report Summary
Self-assembled quantum dots based on use of dilute nitride semiconductors
| Project/Area Number |
17360135
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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 |
Electronic materials/Electric materials
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| Research Institution | University of Tsukuba |
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Principal Investigator |
OKADA Yoshitaka University of Tsukuba, Graduate School of Pure and Applied Sciences, Associate professor (40224034)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Quantum dots / Self-assembled growth / Dilute nitride semiconductors / Strain-control / Molecular beam enitaxy(MBE) / High efficiencv solar cells |
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| Research Abstract |
First, self-assembled Ga_xIn_<1-x> N_yAs_<l-y> quantum dot structures fabricated on GaAs (001) substrates have been studied with atomic-Hydrogen assisted molecular beam epitaxy and a radio frequency nitrogen plasma source. The GaInNAs quantum dots are promising for extending emission wavelengths from 1. 3 to 1.55 um and beyond. We succeeded in achieving high densities on the order of 1. 1x10^<11> cm^<-2> for Ga_<0.53> In_<0.47> No_<0.02> As_<0.98> quantum dots on GaAs (001). Further, we studied the effect of H_2 flux on both the growth dynamics and the optical properties, and found that an optimum H_2 flux rate for Ga_<0.53> In_<0.47> No_<0.02> As_<0.98> quantum dot growth in our system is at around 0.6sccm. These results are attributed to originate from improvement of crystal quality of GaInNAs quantum dots by irradiation of atomic H.
Next, we investigated a growth technique to fabricate multiple-stacked InAs self-assembled quantum dots on GaAs (001) substrates. The stacking of dots is achieved by strain compensation technique, in which GaNAs is used as a spacer layer to bury a quantum dot layer. No dislocations are observed even after 20 layers of stacking, and the area density of quantum dots amounted to the order of 10^<12> cm^<-2>. From photoluminescence measurements, a single emission peak from quantum dots is clearly observed at around 1200 nm at room temperature. Further, the emission peak energy straightforwardly shifts to longer wavelengths with increasing N composition in GaNAs spacer layer due to the lowering the quantum confinement energy or barrier height.
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