InP半导体闪烁体中空穴的Levy飞行
Levy Flight of Holes in InP Semiconductor Scintillator
摘要：
高辐射效率在中度掺杂的n-InP的结果在传输的空穴占主导地位的光子辅助跳跃，当在一个点的辐射空穴复合产生一个光子，其带间吸收产生另一个孔，可能很远。由于跳跃概率中的“重尾”，这是一个具有发散扩散率的随机行走（称为Levy飞行的过程）。我们的关键证据是来自透射和反射的发光光谱的比例，在不同厚度的样品中测量。这些实验证明了空穴浓度从初始光激发点开始的非指数衰减。幂律衰减是利维飞行的特征，在短距离下（比指数更陡），足以拟合薄样本的数据，而在长距离下，则足够慢，足以解释厚样本。高辐射效率使得具有有效光子收集的半导体闪烁体成为可能。这种材料在其自身闪烁的波长下是“不透明的”，这是相当不寻常的。然而，在重复循环之后，大多数光子找到了它们的方式，到达集成在半导体板两侧的两个光电二极管中的一个。我们提出了一个光子在双面平板中收集的解析模型，该模型表明Levy-flight输运的重尾导致了接近理想的特性。最后，我们讨论了一种可能性，以增加板的厚度，同时仍然量化的沉积能量和相互作用的位置内的板。这个想法是使用一个分层的半导体与光子辅助收集的空穴在窄带隙层间隔的距离远远超过扩散长度。在这些辐射层中收集的空穴发射长波辐射，整个结构对长波辐射是透明的。毫米厚的层状闪烁体的接近理想的计算特性可以按比例放大到几厘米。
英文摘要：
High radiative efficiency in moderately doped n-InP results in the transport of holes dominated by photon-assisted hopping, when radiative hole recombination at one spot produces a photon, whose interband absorption generates another hole, possibly far away. Due to "heavy tails" in the hop probability, this is a random walk with divergent diffusivity (process known as the Levy flight). Our key evidence is derived from the ratio of transmitted and reflected luminescence spectra, measured in samples of different thicknesses. These experiments prove the non-exponential decay of the hole concentration from the initial photo-excitation spot. The power-law decay, characteristic of Levy flights, is steep enough at short distances (steeper than an exponent) to fit the data for thin samples and slow enough at large distances to account for thick samples. The high radiative efficiency makes possible a semiconductor scintillator with efficient photon collection. It is rather unusual that the material is "opaque" at wavelengths of its own scintillation. Nevertheless, after repeated recycling most photons find their way to one of two photodiodes integrated on both sides of the semiconductor slab. We present an analytical model of photon collection in two-sided slab, which shows that the heavy tails of Levy-flight transport lead to near-ideal characteristics. Finally, we discuss a possibility to increase the slab thickness while still quantifying the deposited energy and the interaction position within the slab. The idea is to use a layered semiconductor with photon-assisted collection of holes in narrow-bandgap layers spaced by distances far exceeding diffusion length. Holes collected in these radiative layers emit longwave radiation, to which the entire structure is transparent. Nearly-ideal calculated characteristics of a mm-thick layered scintillator can be scaled up to several centimeters.
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