Probing Local Emission Properties in InGaN/GaN Quantum Wells by Scanning Tunneling Luminescence Microscopy

Abstract

Scanning tunneling electroluminescence (STL) microscopy is performed on a 3 nm‐thick InGaN/GaN quantum well (QW) with [In] = 0.23 such that the main light emission occurs in the green. The technique is used to map the radiative recombination properties at a scale of a few nanometers and correlate the local electroluminescence map with the surface topography simultaneously imaged by scanning tunneling microscopy. While the expected green emission is observed all over the sample, measurements performed on a 500 nm × 500 nm area around a 150 nm‐large and 2.5 nm‐deep hexagonal defect reveal intense emission peaks at higher energies close to the defect edges, features which are not visible in the macrophotoluminescence spectrum of the sample. Via a fitting of the local tunneling electroluminescence spectra, quantitative information on the fluctuations of the intensity, peak energy, width, and phonon replica intensity of the different spectral contributions is obtained, which provides information on carrier localization in the QW. This procedure also indicates that the carrier diffusion length on the probed area of the QW is shorter than 50 nm.

Injection mechanisms in a III -nitride light-emitting diode as seen by self-emissive electron microscopy

“…Since then, various reports on the improvement of forward voltage and thus wall-plug efficiency of LEDs with intentional V-defect nucleation have been published, experimentally demonstrating that V-defects provide beneficial carrier injection [12,[21][22][23]. There are reports on higher-energy emission from the lower In content QWs in V-defect sidewalls measured via local excitation by scanning tunneling luminescence in a green LED [24]and observed in the electroluminescence (EL) spectra of green -red LEDs, confirmed to be coming from V-defect sidewalls via micro-photoluminescence [25], suggesting that V-defect sidewalls may have significant population of carriers from injection. Simulations also suggest that V-defects provide beneficial carrier injection [16,17], however there have not been any direct experimental demonstrations on whether carriers do in fact inject laterally.…”