Abstract
A method to detect optical modes from vertical InGaAs nanowires (NWs) using cross-polarization microscopy is presented. Light scattered from the optical modes in the NWs is detected by filtering out the polarized direct reflection with a crossed polarizer. A spectral peak and a valley were seen to red-shift with increasing NW diameter in the measured spectra. The peak was assigned to scattering from the TE01 optical mode and the valley was an indication of the HE11 mode, based on finite-element and scattering matrix method simulations. The cross-polarization method can be used to experimentally determine the spectral positions of the TE01 and HE11 optical modes. The modes are significantly more visible in comparison to conventional reflectance measurements. The method can be beneficial in the characterization of NW solar cells, light-emitting diodes and lasers where precise mode control is required.
Highlights
Reflectance spectroscopy has emerged as an important tool for the optical characterization of NWs
The InGaAs NW arrays were fabricated on a GaAs (111)B substrate using atmospheric pressure selective-area metalorganic vapour phase epitaxy (MOVPE)
The diameters of the NW arrays were measured from topview scanning electron microscope (SEM) images
Summary
Reflectance spectroscopy has emerged as an important tool for the optical characterization of NWs. A method to detect the optical modes from vertical InGaAs NW arrays with a reflectance setup in cross-polarization configuration is presented and compared to conventional reflectance spectroscopy. With this cross-polarization method, the directly reflected light from the NWs and substrate is filtered out using a polarizer, allowing the detection of scattered light only from the NWs. By using finite-element method and scattering matrix method simulations, the scattered light can be attributed to light interacting mainly with the TE01 optical mode. Here the optical modes are characterized directly from NW arrays vertically standing on the substrate without additional processing. The information could be used to estimate the positions of other optical modes, and it is beneficial when NWs are to be used in solar cells, LEDs or in other optoelectronical applications where the optimization of the optical modes is essential
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