Babak Nikoobakht, Amit Agrawal, Scott A. Wight, Jonathan Lee, Michael Shur
Nanostructured semiconductors have shown great promise toward miniaturization of electrically driven semiconductor lasers. Previously, we reported on an electrically driven sub-micron size ZnO-GaN fin LED architecture that at high current densities showed a droop-free behavior and achieved lasing. In this work, we provide a deeper analysis of lateral ZnO fins as an optical gain medium and an optical resonator to better understand their unexpected performance. As a gain medium, its ultraviolet (UV) excitonic emission is explored, and contrasted with upright ZnO nanostructures and bulk ZnO single crystals. Using cathodoluminescence (CL) and electroluminescence (EL) spectroscopies, the impact of temperature on excitonic transitions in two temperature ranges of 5K to 298 K and 298K to 383 K is investigated. Results show the efficiency of electron-hole (e-h) pair collection in lateral nanofins (fins) is directly dependent on the temperature, i.e., as the heterojunction temperature increases, more carrier confinement occurs within the fin. Furthermore, its planar geometry and large interface with the GaN substrate becomes advantageous in heat dissipation. As an optical cavity, we analyzed the fin in terms of the extracted light and the light that is trapped within the cavity. Wavelength- and angle-resolved CL spectroscopy of the emitted light reveal interference fringes due to light reflection from the internal sidewalls. These fringes depend on the fin cavity height and, interestingly, are only observed for UV wavelengths of light. Results show ZnO due to its large exciton binding energy, and the fin-shape could be a great candidate both for enhancing the internal quantum efficiency, and for realization of bright, small footprint cavities for LED and surface emitting UV laser applications.
, Agrawal, A.
, Wight, S.
, Lee, J.
and Shur, M.
ZnO fin optical cavities, Journal of Physical Chemistry C, [online], https://doi.org/10.1021/acs.jpcc.2c02068, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934439
(Accessed November 29, 2023)