High-Resolution Photocurrent Microscopy Using Near-Field Cathodoluminescence of Quantum Dots
Heayoung Yoon, Youngmin Lee, Christopher C. Bohn, Seung H. Ko, Anthony G. Gianfrancesco, Jonathan S. Steckel, Seth Coe-Sullivan, Albert A. Talin, Nikolai B. Zhitenev
We report a fast, versatile photocurrent imaging technique to visualize the local photo response of solar energy devices and optoelectronics using near-field cathodoluminescence (CL) from a homogeneous quantum dot layer. This approach is quantitatively compared with direct measurements of high-resolution Electron Beam Induced Current (EBIC) using a thin film solar cell (n-CdS / p-CdTe). Qualitatively, the observed image contrast is similar, showing strong enhancement of the carrier collection efficiency at the p-n junction and near the grain boundaries. The spatial resolution of the new technique, termed Q-EBIC (EBIC using quantum dot phosphor), is determined by the absorption depth of photons, ≈150 nm in the CdTe solar cell at the wavelength of ≈620 nm. The results demonstrate a new method for high-resolution, sub-wavelength photocurrent imaging measurement relevant for wide range of applications.