Photoconductivity of Quasicrystalline Alloys : Electronic Structure Investigation as a Semiconductor

用两种不同激发能量的激光器对高阻Al-Pd-Re准晶进行了调制光电流测量，该测量最初是为分析半导体的电子态而发展的。两种激发能之间的相移没有明显的差别。调制光电流的幅值和相移数据可以用一个简单的模型很好地解释，该模型只涉及载流子产生和复合两个过程。复合时间比传统半导体的报告时间大了大约六个数量级。从电子态密度和载流子迁移率与能量的关系两个方面对所得结果进行了讨论。将调制光电流法应用于纯的和掺钒的β-菱面体B(β-B)，研究了它们之间禁带中电子态分布的差异。激发光强对光电流幅值和相移的依赖关系表明，掺V的β-B对光激发载流子的俘获态密度比纯β-B大得多。随着温度的升高，纯和掺V的β-B的光激发载流子的俘获态密度分别增大和减小，表明两种样品的光激发载流子的导电机制完全不同。掺V的β-B与Al-Pd-Re准晶的反常负温度依赖关系相似，从正到负的变化与掺V到β-B的铝基二十面体准晶的原子结构和输运性质一致。振幅和相移的调制频率依赖关系不能用通常的光导过程来解释，这表明这些材料的带隙态分布和光导过程是复杂的。

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.