Fourier transform study of the complex electric field induced on axially heterostructured nanowires

Abstract

We present in this work a study of the effect of Raman enhancement on axially heterostructured semiconductor nanowires (NWs). The investigation is motivated by the recent detection of a Raman signal enhancement effect at the heterojunction (HJ) of axially heterostructured NWs. Semiconductor NWs offer very interesting properties as compared to their bulk counterparts, making them the building blocks of future optoelectronic nanodevices. The use of HJs turns out to be essential for a great variety of devices. As a result, understanding the optical properties of heterostructured NWs is a fundamental step for their possible application on future technologies. In order to unveil the underlying physics of the light/NW interaction, the complex-valued electromagnetic (EM) field distribution induced inside heterostructured NWs under light exposure is studied. The use of the Fourier transform is presented as a key tool in order to ascertain the different components of the EM field generated inside the NW. The results show the presence of two components: one associated with the incident light beam and a second one which appears as a consequence of the presence of the axial HJ. This second component explains the emergence of the Raman enhancement effect as a result of the interaction of the incident beam with the dielectric discontinuity associated with the HJ.

3D field confinement in the near-field interaction between graphene and Si/SiGe axially heterostructured NWs

“…In order to confirm this, a 2D laser scan of the NW was performed in order to study the role of the HJs with respect to the Raman signal of graphene. As shown in previous works, [26][27][28]32 the axial HJs give additional light absorption resonances enhancing the Raman signal with respect to the homogeneous segments of the NW. The results of the 2D scanning are summarized in Fig.…”

“…The graphene signal level is rather homogeneous throughout the NW; however, a minimum can be observed when the laser beam runs across the Si/SiGe HJ. A priori we expected the graphene Raman signal to be enhanced by the HJ because of the resonance absorption at the HJ, 26,32 similarly to the SiGe Raman intensity in Fig. 3.…”