Photoconductivity of Quasicrystalline Alloys : Electronic Structure Investigation as a Semiconductor

本文用两种不同激发能量的激光对高电阻率Al-Pd-Re准晶进行了调制光电流测量。在两个激发能量之间的相移中没有发现明显的差异。调制光电流的幅度和相移数据可以用一个简单的模型很好地解释，其中只涉及两个过程，载流子的产生和复合。复合时间比传统半导体的报告大约六个数量级。用调制光电流方法研究了纯β-菱面体硼（β-B）和钒（V）掺杂β-菱面体硼（β-B）带隙中电子态分布的差异。光电流的振幅和相移与激发光强的关系表明，掺V β-B比纯β-B具有更大的光生载流子俘获态密度;随着温度的升高，纯β-B和掺V β-B的振幅分别增大和减小，表明两种样品的光生载流子导电机制完全不同。V掺杂的β-B的反常的负温度依赖性与Al-Pd-Re准晶相似，并且这种由正到负的温度依赖性的变化与V掺杂的β-B在原子结构和输运性质上接近于铝基二十面体准晶相一致。这表明这些材料中的差距态分布和光电导过程是复杂的。

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.