Spatial distribution of photoluminescence ͑PL͒ with spectral, spatial, and/or time resolution has been assessed in an In x Ga 1Ϫx N single-quantum-well ͑SQW͒ structure using scanning near-field optical microscope ͑SNOM͒ under illumination-collection mode at 18 K. The near-field PL images revealed the variation of both intensity and peak energy in PL spectra according to the probing location with the scale less than a few hundredths of a nanometer. PL linewidth, the value of which was about 60 meV in macroscopic PL, was as small as 11.6 meV if the aperture size was reduced to 30 nm. Clear spatial correlation was observed between PL intensity and peak wavelength, where the regions of strong PL intensity correspond to those of long wavelength. Time-resolved SNOM-PL study showed the critical evidence that supports the model of diffusion of carriers to potential minima.
Nonradiative recombination processes of carriers in InGaN/GaN probed by the microscopic transient lens spectroscopy Rev. Sci. Instrum. 74, 575 (2003); 10.1063/1.1519666Time-resolved photoluminescence of quaternary AlInGaN-based multiple quantum wells Precise identification of recombination dynamics based on local, radiative, and nonradiative recombination has been achieved at room temperature in a blue-light-emitting In x Ga 1Ϫx N/GaN single-quantum-well structure by comparing the photoluminescence ͑PL͒ spectra taken by illumination-collection mode ͑I-C mode͒ and those by illumination mode ͑I-mode͒ in scanning near-field microscopy. The PL data mapped with PL lifetimes, as well as with PL spectra, revealed that the probed area could be classified into four different regions whose dominating processes are ͑1͒ radiative recombination within a probing aperture, ͑2͒ nonradiative recombination within an aperture, ͑3͒ diffusion of photogenerated excitons/carriers out of an aperture resulting in localized luminescence, and ͑4͒ the same diffusion process as ͑3͒, but resulting in nonradiative recombination.
Optical properties induced by two major effects, potential fluctuation and piezoelectric fields, have been assessed to interpret the emission mechanism in low-dimensional nitride semiconductors because the former leads to the exciton/carrier localization, and the latter to the quantum confined Stark effect (QCSE). Degenerated white-light pump-and-probe spectroscopy has been employed to assess which factor plays an important role in the series of In x Ga 1-x N multiple quantum well (MQW) structures whose well widths are 3 nm, 5 nm and 10 nm. Moreover, photoluminescence (PL) mapping with scanning near-field optical microscopy (SNOM) has revealed the dense distribution of island-like structures, the size of which ranges from 20 nm to 70 nm in a 3 nm-thick In x Ga 1-x N single quantum well (SQW) structure emitting at blue spectral region. The most devices are grown toward c-direction with hexagonal structures, so that large internal electric field is induced to the growth direction. This electric field is in the order of MV/cm, so the optical dipole, as well as transition energies is reduced due to the separation between electron and hole wavefunctions. Such effects are called as Franz-Keldysh effect and quantum confined Stark effect (QCSE). The second one is potential fluctuation induced by inhomogeneity of both In compositions and well widths. This limits the number of density of states due to the formation of localized tail states. Because of these effects, large Stokes shift between absorption and emission is observed, as well as significant blue shift of emission energy with increasing injected-carrier density. The problem is that it is very difficult to know with conventional optical measurement which factor limits the recombination mechanism because both two effects can contribute to observed phenomena. It should be noted here that the major factor changes with the sample, because the effect of internal electric field is enhanced with increasing well width, and is reduced with increasing background doping concentration and with carrier injection, and also the degree of potential fluctuation is changed with the difference in growth conditions. Therefore, the precise optical characterization is needed in each sample to determine the recombination mechanism.
PACS: 68.37.Uv; 78.60.Fi Electroluminescence (EL) mapping has successfully been performed for In x Ga 1--x N single quantum well (SQW)-based light emitting diodes (LEDs) by employing scanning near-field optical microscopy (SNOM) at room temperature. The relative EL intensity fluctuates in the range from 1 to 4 with the spatial scale less than a few hundred nanometers. Clear correlation has been found between EL peak wavelengths and EL intensities where the regions of long wavelength correspond to those of strong EL intensity, suggesting that the injected carriers redistribute toward local potential minima within In x Ga 1--x N SQWs.
Spatial distribution of photoluminescence (PL) spectra has been assessed in an InGaN single quantum well (SQW) structure by means of fluorescence microscopy and scanning near-field optical microscopy (SNOM) under illumination-collection mode. The PL intensity of fluorescence image is uniform at 77 K, but the dark spot areas were extended with increasing temperature. The nearfield PL images revealed the variation of both peak energy and intensity in PL spectra according to the probing location with the scale less than a few hundreds nm. phys. stat. sol. (b) 228, No. 1, 153-156 (2001) # WILEY-
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.