| Project/Area Number |
06452102
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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 |
Applied materials science/Crystal engineering
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| Research Institution | University of Tsukuba |
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Principal Investigator |
TAKITA Koki Institute of Materials Sciences University of Tsukuba Professor, 物質工学系, 教授 (00011213)
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| Co-Investigator(Kenkyū-buntansha) |
KURODA Shinji Institute of Materials Sciences University of Tsukuba Lecturer, 物質工学系, 講師 (40221949)
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| Project Period (FY) |
1994 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 1996: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 1995: ¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1994: ¥3,500,000 (Direct Cost: ¥3,500,000)
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| Keywords | diluted magnetic semiconductors / multiple quantum well / magneto-optics / gigantic Zeeman splitting / type I-type II transition / heterointerface / interdiffusion / segregation / 磁気光吸収 / typeI→II転移 |
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| Research Abstract |
Artificial heterostructures consisting of diluted magnetic semiconductors (DMS) and non-magnetic semiconductors, such as CdTe/Cd_<1-x>Mn_xTe superlattices (SLs), electronic states quantized in the SL potential are modified by the exchange interaction which takes place only in the DMS layr. In other words, electronic properties of CdTe/Cd_<1-x>Mn_xTe SLs can be tuned by applying magnetic fields through the gigantic Zeeman splitting of DMS layr (Zeeman tuning). In this study, the magneto-optical properties of CdTe/Cd_<1-x>Mn_xTe multiple quantum wells (MQWs) were investigated with a special emphasis on the following two topics.
a) Magnetic-field induced type I-type II transition
We studied the type I-type II transition in MQWs with relatively large Mn concentration of about 0.3. In such MQWs with large valence-band offset, the type transition is expected to take place at very high magnetic fields. Then we measured magneto-absorption spectra under pulsed magnetic fields up to 150 T produced
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by the single-turn coil technique. As a result, we found evident features associated with the type transition-diminution of the absorption intensity and the onset of a red-shift of the heavy-hole exciton energy. These observed features were reproduced qualitatively well by a variational calculation when valence-band offset ratio is assumed to be 30-40%.
b) Magneto-optical study of broadening at the heterointerface
In the heterointerface of an actual SLs, there always exists broadening-the change of composition across the interface is not parfectly abrupt but broadened owing to various process in the crystal growth. This interface broadening is expected to enhance the gigantic Zeeman splitting of the exciton confined in the CdTe well layr, because the magnetization of the broadened region becomes larger than that of the Cd_<1-x>Mn_xTe layr. Therefore from the observed Zeeman splitting the degree of the interface broadening can be estimated by comparing it with a model calculation. We investigated the degree of the interface broadening in MQW samples grown at various growth conditions, such as flux ratio of II/VI elements, substrate temperatures and thermal annealing after the growth. As a result, it was found that the dependence of the broadening lengths on the substrate temperature is different according as the MBE growth was performed in the excess of Cd or Te flux. From this it is deduced that the interface broadening is caused by the thermal diffusion of Cd and Mn atoms in the case of Te-excess growth and is caused by the segregation in the case of Cd-excess growth. Less
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