Observation of photo-excited carrier dynamics in semiconductors with time, space, and energy resolutions
Observation of photo-excited carrier dynamics in semiconductors with time, space, and energy resolutions
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在时间、空间和能量分辨率下观察半导体中的光激发载流子动力学
DOI：
10.11470/jsaprev.220406
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Keiki Fukumoto/Shin-ya Koshihara
中科院分区：
文献类型：
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作者：
蓑和怜央;櫻井英博;佐々木成朗;Keiki Fukumoto/Shin-ya Koshihara
自1950年左右晶体管发明以来，半导体已被用于太阳能电池、发光二极管（LED）和各种其他器件。虽然Si是典型的半导体材料，但最近基于材料探索开发了其性能无法通过使用Si实现的器件。这种器件的示例包括利用诸如SiC和GaN的宽禁带半导体的电力电子器件、利用有机半导体的柔性的可穿戴器件以及使用诸如石墨烯或过渡金属二硫属化物的二维材料的低能耗晶体管。这些发展使得能够通过高纯度晶体生长显著降低作为电荷转移障碍的缺陷密度，并且通过成分选择和优化异质界面控制能带结构来控制电荷转移。在半导体器件中，电荷载流子（电子和空穴）在从飞秒到秒的广泛时间尺度上移动，并且在从纳米到微米的空间范围内移动。然而，直接观察这些电荷载体运动的方法，即跟踪导电电子在时间和空间上的运动的方法尚未建立。电荷载流子的动态特性，特别是它们的迁移率和复合寿命，是决定半导体器件工作性能的关键因素。迁移率与器件的工作速度直接相关，可以使用霍尔效应和微波电导率测量等方法进行测量。在红外光或微波吸收的时间变化中观察到寿命，并且使用光学泵浦-探测光谱法测量光电子谱。必须考虑器件工作频率的寿命。将这些方法用于纳米级空间分辨率是具有挑战性的。具有高空间分辨率的扫描显微镜需要延长的时间来观察时间演化过程，同时从纳米空间映射微小信号，这在技术上很难实现时间分辨率。为了解决这些问题，我们已经开发出一种飞秒光电子发射显微镜（fs-PEEM），结合成像型光电子发射显微镜和泵浦探测光谱使用飞秒脉冲激光。
Since the invention of the transistor around 1950, semiconductors have been used in solar cells, light-emitting diodes (LEDs), and various other devices. Although Si is a typical semiconductor material, devices whose properties cannot be achieved by using Si have been recently developed based on material exploration. Examples of such devices include power electronics that utilize wide-gap semiconductors such as SiC and GaN, wearable devices that utilize the flexibility of organic semiconductors and low energy consumption transistors using two-dimensional materials such as graphene or transition metal dichalcogenides. These developments have enabled the significant reduction of defect density, which is an obstacle to charge transfer, through high purity crystal growth, and the control of charge transfer by controlling the band structure through composition selection and optimizing hetero-interfaces. In semiconductor devices, charge carriers (electrons and holes) move on a wide range of time scales from femtoseconds to seconds, and in the space rage from nanometer to micrometer. However, a method for directly observing the movement of these charge carriers, that is, for tracking the movement of the conducting electrons in time and space, has not yet been established. The dynamic properties of charge carriers, particularly their mobility and recombination lifetime, are critical factors determining the operating performance of semiconductor devices. Mobility is directly related to the operating speed of the device and can be measured using methods such as the Hall effect and microwave conductivity measurements. The lifetime is observed in the time variation in the infrared light or microwave absorption and the photoelectron spectra measured using optical pump-probe spectroscopy. The lifetime must be considered for the operating frequency of the devices. It is challenging to use these methods for nanoscale spatial resolution. Scanning microscopes with high spatial resolution require extended time to observe the time evolution process while mapping minute signals from nano-space, technically making it difficult to achieve temporal resolution. To solve these problems, we have developed a femtosecond photoelectron emission microscope (fs-PEEM) that combines imaging-type photoelectron emission microscopy and pumpprobe spectroscopy using a femtosecond pulse laser.