Kohandani Reza, Saini Simarjeet S
Department of Electrical and Computer Engineering, University of Waterloo, 200 University Ave West, Waterloo, ON, N2L 3G1, Canada.
Nanotechnology. 2022 Jul 7;33(39). doi: 10.1088/1361-6528/ac74cc.
A method based on extraction of the effective absorption coefficient using Beer-Lambert's law on simulated transmissions is used to understand the optical absorption characteristics of semiconductor nanowire arrays. Three different semiconductor nanowire arrays, viz. silicon (Si), gallium arsenide (GaAs) and amorphous silicon (a-Si), are evaluated using the method. These semiconductors were chosen since two of them have similar real parts of the refractive index in the visible range, while the other two have comparable imaginary parts of the refractive index in the visible range. We examine the roles of the real and imaginary parts of the refractive index in enhancing the absorption characteristics in the nanowire arrays due to the excitation of radial and photonic Bloch modes. We observe that high absorption peaks at modal resonances correspond to the resonance peaks in reflections from the nanowire-air interface. Further, the wavelengths of these two peak resonances are slightly detuned according to the Kramers-Kronig relation for an oscillator system. The study confirms that the resonance wavelengths of radial HE modes are diameter and refractive index dependent. The study extends the understanding to the absorption characteristics due to the excitation of the photonic Bloch modes caused by near-field coupling. Excitation of Bloch modes leads to increased absorption and quality factor as compared to only radial mode excitation. We also conclude that the imaginary part of the refractive index of the semiconductor, influence the diameters at which Bloch modes are excited for a given lattice spacing. We observe that semiconductors with a higher bulk value of absorption coefficient need to be ordered more densely in the nanowire array to be able to excite the photonic crystal modes within the array. Interestingly, we see that for Si, GaAs and a-Si arrays with an equal diameter of 80 nm and lattice spacing of 400 nm, the peak absorption is almost the same, even though GaAs and a-Si are highly absorptive materials compared to Si. Thus, both radial and Bloch mode excitations can be used to design absorption profiles in a semiconductor nanowire array.
一种基于利用比尔-朗伯定律从模拟传输中提取有效吸收系数的方法，被用于理解半导体纳米线阵列的光吸收特性。使用该方法评估了三种不同的半导体纳米线阵列，即硅（Si）、砷化镓（GaAs）和非晶硅（a-Si）。选择这些半导体是因为其中两种在可见光范围内具有相似的实部折射率，而另外两种在可见光范围内具有可比的虚部折射率。我们研究了折射率的实部和虚部在由于径向和光子布洛赫模式的激发而增强纳米线阵列吸收特性方面的作用。我们观察到，模态共振处的高吸收峰对应于纳米线-空气界面反射中的共振峰。此外，根据振荡器系统的克拉默斯-克勒尼希关系，这两个峰值共振的波长略有失谐。研究证实，径向HE模式的共振波长与直径和折射率有关。该研究将理解扩展到由于近场耦合引起的光子布洛赫模式激发导致的吸收特性。与仅径向模式激发相比，布洛赫模式的激发导致吸收增加和品质因数提高。我们还得出结论，半导体折射率的虚部会影响在给定晶格间距下激发布洛赫模式的直径。我们观察到，具有较高体吸收系数值的半导体需要在纳米线阵列中更密集地排列，以便能够激发阵列内的光子晶体模式。有趣的是，我们发现对于直径均为80nm且晶格间距为400nm的Si、GaAs和a-Si阵列，即使GaAs和a-Si与Si相比是高吸收性材料，其峰值吸收几乎相同。因此，径向和布洛赫模式激发都可用于设计半导体纳米线阵列中的吸收分布。
