We report on diffusion-driven and excitation-dependent carrier recombination rate in multiple InGaN/GaN quantum wells by using photoluminescence, light-induced absorption, and diffraction techniques. We demonstrate gradually increasing with excitation carrier diffusivity and its correlation with the recombination rate. At low carrier densities, an increase in radiative emission and carrier lifetime was observed due to partial saturation of non-radiative recombination centers. However, at carrier densities above ∼5 × 1018 cm−3, a typical value of photoluminescence efficiency droop, a further increase of diffusivity forces the delocalized carriers to face higher number of fast non-radiative recombination centers leading to an increase of non-radiative losses.

The measurement of the energy distribution of vacuum emitted electrons from InGaN/GaN light-emitting diodes (LEDs) has proven essential in understanding the efficiency loss mechanism known as droop. We report on the measurement and identification of a new low-energy feature in addition to the previously measured three peaks present in the electron emission spectrum from a forward biased LED. Photoemission measurements show that the two low-energy peaks correspond to photoemitted electrons from each of the p-contact metals, palladium and gold. We confirm that the mid and high-energy peaks are due to electrons which have transited the p-type region of the device and have been emitted from the semiconductor surface from the bulk Γ-valley or a high-energy side valley.

We report on the direct measurement of hot electrons generated in the active region of blue light-emitting diodes grown by ammonia molecular beam epitaxy by electron emission spectroscopy. The external quantum efficiency of these devices is <1% and does not droop; thus, the efficiency losses from the intrinsic, interband, electron-electron-hole, or electron-hole-hole Auger should not be a significant source of hot carriers. The detection of hot electrons in this case suggests that an alternate hot electron generating process is occurring within these devices, likely a trap-assisted Auger recombination process.

Energy measurements of electrons emitted from a semiconductor can reveal internal physical processes hitherto elusive. Signatures of hot-electron processes in heterostructures have been observed from cesiated, light-emitting and p-in diodes. In pin devices with AlGaN barriers, a high energy peak was measured and ascribed to a trap-assisted Auger recombination process. Temperature dependent measurements of light-emitting diodes with AlGaN electron blocking layers also show such hot carriers when electrons thermally reach these barriers, identifying carrier escape as the mechanism of thermal droop and demonstrating the efficacy of such barriers to partially mitigate thermal droop.

Articles you may be interested inTemporally and spatially resolved photoluminescence investigation of ( 11 2 ¯ 2 ) semi-polar InGaN/GaN multiple quantum wells grown on nanorod templates Appl. Phys. Lett. 105, 261103 (2014); 10.1063/1.4905191Highly polarized photoluminescence and its dynamics in semipolar ( 20 2 ¯ 1 ¯ ) InGaN/GaN quantum well Appl. Phys. Lett.High optical polarization ratio of semipolar ( 20 2 ¯ 1 ¯ ) -oriented InGaN/GaN quantum wells and comparison with experiment J. Appl. Phys. 112, 093106 (2012); 10.1063/1.4764316 Dynamics of polarized photoluminescence in m -plane InGaN/GaN quantum wellsScanning near-field optical spectroscopy was applied to study spatial variations of emission spectra at room temperature in semipolar ð20 21Þ In x Ga 1Àx N/GaN single quantum wells (QWs) for 0:11 x 0:36. Photoluminescence (PL) was found to be highly uniform, with peak wavelength deviations and peak intensity deviations divided by average values in the range of 6-12 meV and 0.03-0.07, respectively. Near-field maps of PL parameters showed large, $5 to 10 lm size areas of similar values, as opposed to 100 nm scale variations, often reported for InGaN QWs. The nearfield PL spectra were found to broaden with increasing InN molar fraction. In the low In content QWs, the broadening is primarily determined by the random cation distribution, while for larger InN molar fractions 10 nm scale localization sites with increasingly deeper band potentials are suggested as the linewidth broadening cause. V C 2015 AIP Publishing LLC.

Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202¯1) InGaN quantum wells (QWs) emitting in violet, blue, and green-yellow spectral regions. With increased excitation power, an untypical PL peak energy shift to lower energies was observed. The shift was attributed to carrier density dependent carrier redistribution between nm-scale sites of different potentials. Near-field PL scans showed that in (202¯1) QWs the in-plane carrier diffusion is modest, and the recombination properties are uniform, which is advantageous for photonic applications.

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