Nanoscale Relative Emission Efficiency Mapping Using Cathodoluminescence g⁽²⁾ Imaging

Abstract

Cathodoluminescence (CL) imaging spectroscopy provides two-dimensional optical excitation images of photonic nanostructures with a deep-subwavelength spatial resolution. So far, CL imaging was unable to provide a direct measurement of the excitation and emission probabilities of photonic nanostructures in a spatially resolved manner. Here, we demonstrate that by mapping the cathodoluminescence autocorrelation function g(2) together with the CL spectral distribution the excitation and emission rates can be disentangled at every excitation position. We use InGaN/GaN quantum wells in GaN nanowires with diameters in the range 200–500 nm as a model system to test our new g(2) mapping methodology and find characteristic differences in excitation and emission rates both between wires and within wires. Strong differences in the average CL intensity between the wires are the result of differences in the emission efficiencies. At the highest spatial resolution, intensity variations observed within wires are the result of excitation rates that vary with the nanoscale geometry of the structures. The fact that strong spatial variations observed in the CL intensity are not only uniquely linked to variations in emission efficiency but also linked to excitation efficiency has profound implications for the interpretation of the CL data for nanostructured geometries in general.

Efficient Green Emission from Wurtzite AlxIn1–xP Nanowires

“…The intensity variations observed in Figure 2 e when probing the core are likely due to lower excitation efficiency and therefore lower emission from the edges and tip of the nanowire. 24 , 25 …”

Nanoscale Structural and Emission Properties within “Russian Doll”‐Type InGaN/AlGaN Quantum Wells

“…Then, CL spectroscopy was performed to investigate the specific local optical properties of the synthesized InGaN/AlGaN QWs@GaN NR leading to direct information on the local optical response of such NRs as demonstrated in Figure 2. [38] Figure 2a shows the HAADF-STEM image of the cross sectional view of the FIB sample, which was thinned down to one-nanorod thick (about 200 nm) at very low ion beam voltage (5 keV) in order to study the light emission performance of the whole InGaN/AlGaN QWs stack within the NR. The spatially resolved CL emission wavelengths mapping for the InGaN/ AlGaN QWs, overlaid on the corresponding SEM image, is shown in Figure 2b.…”

Carrier dynamics near a crack in GaN microwires with AlGaN multiple quantum wells

“…Thanks to the specificity of the electron-matter interactions (a single incoming electron creates multiple electron-hole pairs), this technique allows us to measure the carrier lifetime. 23 Its main advantage is the ability to measure carrier lifetime at the nanometer scale without the expense of a pulsed electron gun or ultrafast beam blanker. In details, the collected CL light is sent to two fast photodetectors (PMA Hybrid 06 from Picoquant) thanks to a 50/50 beam splitter.…”

“…To overcome these limitations, time-resolved CL (TR-CL) techniques have been proposed. 21,22 Here, using a spatially resolved time-correlated CL (SRTC-CL) setup, 23,24 we probe the carrier dynamics near cracks in core-shell GaN/AlGaN microwires with a spatial resolution of 50 nm and a temporal resolution better than 40 ps (see supp. material Sec.…”