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

半导体中热载流子的动力学几十年来一直是一个密集的研究课题。从根本上讲，高激发态、几乎自由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发展纳米级半导体器件是至关重要的，因为在纳米级半导体器件中，小电压很容易产生纳米级的热载流子。用强飞秒激光脉冲(λ=780 nm)在块状InAs中产生了热载流子，不仅观察到了斯托克斯发光，而且观察到了令人惊讶的强反斯托克斯发光。此外，在反斯托克斯光谱中发现了一个周期性的强度变化，这可能归因于热载流子的双LO声子级联发射。在双光子吸收过程中产生的热载流子在复合发射一个光子之前可能会产生几对LO声子，并对InAs和InSb的发光空间范围进行了探讨。它比激光光斑大几倍(~2μm)。我们的结果表明，窄禁带半导体中的热载流子可能会以弹道方式传输到令人惊讶的长距离。实验还发现，发光强度与激发激光能量呈现出很强的非线性关系。此外，在FIB装置和加热炉上制备了具有一定点状的双层结构(核壳和轴向超晶格)纳米线。这种双层结构的纳米线由晶态的InSb和In_2O_3组成。该方法简单，可用于大规模生产化合物半导体纳米线。在纳米尺度上操纵镓离子束可以制造纳米电子器件和纳米光电器件。创造这种新型纳米结构的具体条件和机制目前尚不清楚，但我们希望这些发现能引起人们对化合物半导体纳米线研究的更多兴趣。

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.