Semipolar (202¯1) plane InxGa1−xN quantum wells (QWs) of varying alloy composition were studied by time-resolved photoluminescence. A large difference in effective radiative lifetimes, from sub-ns for x=0.11 to ∼30 ns for x≈0.35 was found. This effect is attributed to different properties of carrier localization. In low In content QWs, recombination at extended states with short recombination times is prevalent. In QWs with a high In content, the lifetimes are increased by localization of electrons and holes at separate sites. The zigzag shape of the QW interfaces and the resulting in-plane electric field are proposed as the cause for the separate electron and hole localization.

A multimode scanning near-field optical microscopy technique that allows the mapping of surface morphology, photoluminescence (PL) spectra in illumination and illumination-collection modes, and PL dynamics, all in one scan, has been developed along with a method to use it for evaluation of carrier diffusion. The method allows measuring diffusion lengths as small as ∼100 nm and their anisotropy and spatial distribution, parameters remaining inaccessible to conventional far-field techniques. The procedure has been applied to study ambipolar carrier diffusion in a nonpolar m-plane InGaN/GaN quantum well. The diffusion was found to be highly anisotropic with diffusion coefficients along and perpendicular to the wurtzite c axis equal to 0.4 and 1.9 cm 2 /s, respectively. The large diffusion anisotropy confirms band structure calculations that suggest that the topmost valence band in an m-plane InGaN quantum well is highly anisotropic.

Very high polarization degree of 0.98, considerably larger than theoretical predictions, has been measured in (202¯1¯) In0.24Ga0.76N/GaN quantum well by low temperature photoluminescence. With increasing temperature, the polarization degree decreases due to thermal population of the excited valence band level. This effect suggests an accurate method to determine the interlevel energy, which, for the studied well, is 32 meV. Time-resolved photoluminescence measurements set radiative recombination times between 2 and 12 ns for temperatures from 3 to 300 K. Nonradiative recombination was found to be slow, over 2 ns at 300 K, taking place via traps with activation energy of 0.19 eV.

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.

Time-resolved scanning near-field photoluminescence (PL) spectroscopy was applied to map carrier lifetimes in wide m-plane InGaN/GaN quantum wells grown on on-axis and miscut substrates. Both radiative and nonradiative lifetimes were found to be spatially nonuniform. Lifetime variations were smaller for quantum wells grown on miscut, as compared to on-axis substrates. Correlation with surface topography showed that largest deviations of recombination times occur at +c planes of pyramidal hillocks of the on-axis sample. Observed correlation between radiative lifetimes and PL peak wavelength was assigned to a partial electron localization.