1999 Fiscal Year Final Research Report Summary
Photoconductivity of Quasicrystalline Alloys : Electronic Structure Investigation as a Semiconductor
| Project/Area Number |
09450232
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Physical properties of metals
|
|---|
| Research Institution | The University of Tokyo |
|---|
Principal Investigator |
KIMURA Kaoru The University of Tokyo, Graduate School of Frontier Sciences, Professor, 大学院・新領域創成科学研究科, 教授 (30169924)
|
|---|
| Project Period (FY) |
1997 – 1999
|
| Keywords | Quasicrystal / β-rhombohedral Boron / V-doping / Modulation Method / Photoconductivity / Phase Shift / Icosahedral Cluster Solid |
|---|
| Research Abstract |
Modulated photocurrent measurements, originally developed for analyzing the electronic states of semiconductors have been performed on an Al-Pd-Re quasicrystal having high electrical resistivity using two kinds of Lasers with different excitation energies. No noticeable difference has been found in the phase shift between the two excitation energies. The data of the amplitude and phase shift of modulated photocurrent can be explained well by a simple model in which only the two processes, carrier generation and recombination, are involved. The recombination time is by about six orders larger than those reported for conventional semiconductors. The results obtained are discussed in terms of electron density of states and energy dependence of carrier mobility.
The modulated photocurrent method has been applied to pure and vanadium (V) doped β-rhombohedral boron (β-B), aiming at investigating the difference in the distribution of electronic states in the band gap between them. Excitation light intensity dependence of the amplitude and phase shift of photocurrent shows that V-doped β-B has a much larger trapping states density for photoexcited carriers than pure β-B.With increasing temperature, the amplitude increases and decreases for pure and V-doped β-B, respectively, indicating that the conduction mechanism for photo-excited carrier is completely different between the two samples. The unusual negative temperature dependence for V-doped β-B is similar to that for Al-Pd-Re quasicrystal and the change of dependence from positive to negative is consistent with the approach to aluminum-based icosahedral quasicrystals in atomic structure and in transport properties by V-doping to β-B.The modulated frequency dependence of the amplitude and phase shift cannot be explained by the usual photoconduction processes, which are indicating that the gap states distribution and photoconduction processes in these materials are complicated.
|
