Spatial and temporal spectroscopy of the luminescence generated by hot carriers in narrow-gap-semiconductor quantum dots

几十年来，半导体中热载流子的动力学一直是一个深入的研究课题。从基本的观点来看，高激发态的、几乎自由的载流子的行为以及它们与其他载流子、声子、光子等的相互作用引起了人们极大的兴趣。在应用方面，了解热载流子动力学对于推进纳米级半导体器件至关重要，其中小电压很容易产生纳米级尺寸的热载流子。利用飞秒强激光脉冲（λ=780 nm）在InAs中产生热载流子，不仅观察到Stokes发光，还观察到了非常强的反Stokes发光。此外，在反斯托克斯光谱中发现了一个周期性的强度变化，这可能是由于热载流子的两个LO声子级联发射。双光子吸收过程中产生的热载流子在复合发射光子之前可能会产生多对LO声子，并对InAs和InSb的发光空间范围进行了探讨。它比激光光斑尺寸（102 μ m）大几倍。我们的研究结果表明，窄禁带半导体中的热载流子可能会在惊人的长距离上进行弹道旅行。此外，我们还利用FIB装置和加热炉制备了具有点结构的双结构（核壳结构和轴向超晶格结构）纳米线。双结构纳米线由InSb和In_2O_3晶体组成。该方法简单，可用于大规模制备化合物半导体纳米线。对Ga离子束进行纳米尺度的操控可以使我们制作纳米电子器件和纳米光电器件。目前，产生这种新型纳米结构的详细条件和机制尚不清楚，但我们希望这些发现可以引起人们对化合物半导体纳米线研究的兴趣。

The dynamics of hot carriers in semiconductors has been an intensive research subject for some decades. From a fundamental point of view, the behavior of highly excited, almost free carriers and their interactions with other carriers, phonons, photons and so on is of great interest. Application-wise, understanding the hot carrier dynamics is essential in advancing nano-scale semiconductor devices, where a small voltage easily generates hot carriers in nano-scale dimensions. Intense femto-second laser pulses (λ=780 nm) were used to generate hot carriers in bulk InAs, where not only Stokes luminescence, but also surprisingly strong anti-Stokes luminescence were observed. Moreover, a periodic intensity variation found in the anti-Stokes spectrum was found and may be attributed to two-LO-phonon cascade emission by the hot carriers. Hot carries produced in two-photon absorption process may generate several pairs of LO phonons before they emit a photon by recombination.The luminescence spatial extent was also probed in InAs and InSb. It was several times larger than the laser spot size (〜2 μ m). Our results suggest that hot carriers in the narrow-gap semiconductors may travel ballistically over a surprisingly long distance. It is also noted that the luminescence intensity exhibited large non-linearity with the excitation laser energy.In addition, fabrication of the double structured (core-shell and axial superlattice) nanowires with some dots was conducted with FIB apparatus and a furnace. The double structured nanowires consist of crystalline InSb and In_2O_3. The method is simple and can be used to mass-produce compound semiconductor nanowires. Manipulation of Ga-ion beams in nanoscale may enable us to fabricate nanoelectronics devices and nanophotodevices. The detailed conditions and mechanism for creating such novel nanostructures are not clear at this time, but we hope these findings may invoke more interests in compound semiconductor nanowire research.