Measuring Photonic Bands with Energy-Momentum Spectroscopy

The Monarc® Pro system offers the most comprehensive analysis of cathodoluminescence (CL) emissions on the market. The system empowers users of all experience levels to capture the highest quality data.

Context

There is increasing interest in the development of novel optical devices fabricated from photonic crystals (PhCs) and metamaterials. This attention is primarily due to these devices’ wide range of potential applications, for example, telecommunications, optical computing and micro-LED displays.

PhCs and metamaterials leverage the distinct benefits of coherent scattering and near-field interactions, affording researchers diverse opportunities to manipulate and control light down to the nanoscale.

It is also possible to design PhCs to accommodate specific photonic band structures, allowing these to selectively control the propagation or transmission of light at defined frequencies and directions, in line with the PhC’s periodicity and lattice form.

Optimizing these devices necessitates the precise control of PhC components’ nanoscale arrangement, shape and size and the implementation of experimental techniques to characterize devices’ physical and optical properties.

Materials and Methods

The example presented here illustrates the measurement of a PhC’s photonic bands via energy-momentum (E-k) spectroscopy. It also provides a detailed analysis of the PhC’s physical properties using a scanning electron microscope (SEM) and wavelength- and angle-resolved CL (WARCL).1

The PhC under investigation was comprised of an array of six-sided micro-pillars. Each of these pillars was 810 ± 20 nm wide and had been fabricated from GaN. Each pillar also featured In13Ga87N quantum wells on its outer surfaces. The pillars had been arranged in a two-dimensional hexagonal lattice at 2.0 ± 0.03 μm pitch.

During the experiment, CL emission was excited via a conventional SEM operating at 10 kV. The emitted photons’ emission anisotropy and wavelength distribution were analyzed using the WARCL mode of the Monarc Pro (model 450.P.WAR).

The Monarc Pro system is aberration-corrected, meaning it can facilitate the capture of WARCL data with no reduction or loss in spectral or angular resolutions.

 

 Figure 1. (left) SE image of InGaN/GaN core-shell pillar array in plane-view with (left inset) tilted view of a single pillar, (middle) symmetrically averaged WARCL emission pattern of pillar array extracted from 545 nm, and (right) energy-momentum basis observing k along the a-direction captured with a total acquisition time of 90 s. Image Credit: Gatan Inc.

Summary

The Monarc was employed to capture a semiconductor PhC’s photonic band structure. This allowed the direct correlation of the PhC’s optical properties to its nanoscale structure.

Wavelength-resolved emission patterns were collected in 90 seconds, including patterns from the ultraviolet (350 nm) wavelengths through the visible spectrum (750 nm). These were then converted to the energy-momentum basis to expose the photonic band structure.

The Monarc Pro’s WARCL mode expands researchers’ capacity and ability to characterize light-matter interactions at the nanoscale, offering new avenues in the development of innovative new optical devices.

References

  1. Bertilson, M.; et al., Microscopy and Microanalysis Conference Proceedings (2018)

This information has been sourced, reviewed and adapted from materials provided by Gatan Inc.

For more information on this source, please visit Gatan Inc.

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