Dhindsa Navneet, Kohandani Reza, Saini Simarjeet S
Department of Electrical and Computer Engineering, University of Waterloo, 200, University Avenue West, Waterloo, ON, N2L 3G1, Canada. Currently with ASML, Connecticut, United States of America.
Nanotechnology. 2020 May 29;31(22):224001. doi: 10.1088/1361-6528/ab764a. Epub 2020 Feb 13.
Resonant optical mode excitations in semiconductor nanowires result in enhanced absorptions. Nominally, only the diameter dependent radial mode excitations have been considered for the increased absorption. In this paper, we try to understand how the length of the nanowires affects the resonant wavelength and peak absorption wavelengths. We answer two questions viz (1) at what minimum length are radial optical modes stabilized and dominate the absorption characteristics and (2) do longitudinal modes play a role in absorption characteristics especially in determining the resonant wavelength. Two different semiconductors are studied viz silicon and gallium arsenide. We find that even nanowires as short as 200 nm exhibit absorption characteristics dominated by the radial mode excitation. However, for lengths smaller than 200 nm, the optical characteristics are dominated by scattering. Further, we observe that longitudinal modes are excited in low absorption semiconductor materials like silicon for lengths up to 700 nm and the absorption peak depends both on the diameter and the wavelength. Further, shorter length nanowires may have higher absorption than the longer ones in this regime. We also observed that scattering from the nanowires is less than 2% of the incident light. For higher absorption semiconductor like GaAs, absorption characteristics are mainly determined by the radial mode excitations even for shorter lengths. The results provide further insight into the radial mode excitations in semiconductor nanowires.
半导体纳米线中的共振光学模式激发会导致吸收增强。通常，仅考虑了与直径相关的径向模式激发对吸收增加的影响。在本文中，我们试图了解纳米线的长度如何影响共振波长和峰值吸收波长。我们回答两个问题，即（1）径向光学模式在什么最小长度下稳定并主导吸收特性，以及（2）纵向模式在吸收特性中是否起作用，特别是在确定共振波长方面。研究了两种不同的半导体，即硅和砷化镓。我们发现，即使短至200 nm的纳米线也表现出以径向模式激发为主导的吸收特性。然而，对于长度小于200 nm的情况，光学特性以散射为主导。此外，我们观察到，在长达700 nm的硅等低吸收半导体材料中会激发纵向模式，并且吸收峰取决于直径和波长。此外，在这种情况下，较短长度的纳米线可能比较长的纳米线具有更高的吸收。我们还观察到，纳米线的散射小于入射光的2％。对于像GaAs这样的高吸收半导体，即使对于较短的长度，吸收特性也主要由径向模式激发决定。这些结果为半导体纳米线中的径向模式激发提供了进一步的见解。
