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1

Signal processing for time resolved photoluminescence spectroscopy

Grodecki Kacper, Murawski Krzysztof, Rutkowski Jarosław, Kowalewski Andrzej, Sobieski Jan

Opto-Electronics Review

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2021

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Vol. 29, No. 3

91--96

EN

Accurate determination of material parameters, such as carrier lifetimes and defect activation energy, is a significant problem in the technology of infrared detectors. Among many different techniques, using the time resolved photoluminescence spectroscopy allows to determine the narrow energy gap materials, as well as their time dynamics. In this technique, it is possible to observe time dynamics of all processes in the measured sample as in a streak camera. In this article, the signal processing for the above technique for Hg1-xCdxTe with a composition x of about 0.3 which plays an extremely important role in the mid-infrared is presented. Machine learning algorithms based on the independent components analysis were used to determine components of the analyzed data series. Two different filtering techniques were investigated. In the article, it is shown how to reduce noise using the independent components analysis and what are the advantages, as well as disadvantages, of selected methods of the independent components analysis filtering. The proposed method might allow to distinguish, based on the analysis of photoluminescence spectra, the location of typical defect levels in HgCdTe described in the literature.

2

Optical spectroscopy of polyazomethine-PCBM nanostructures

Korona K. P., Grankowska S., Iwan A., Korona T., Rutkowska-Zbik D., Kamińska M.

Elektronika : konstrukcje, technologie, zastosowania

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2014

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Vol. 55, nr 9

92-94

EN

We report optical properties of a recently synthesized 25Th-cardo polyazomethine (PAZ) and of its mixture with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The polymer film had significant absorption for wavelengths shorter than 480 nm (2.6 eV). The external quantum efficiency of 25Thcardo: PCBM solar cell was the highest (about 0.3%) in the near UV range. Theoretical calculations show that HOMO energy levels are equal to –5.99 eV and –5.95 eV for PAZ and PCBM, respectively. Such a small energy difference enables hole leaking from PAZ to PCBM, what can explain low photo-current yield and presence of PCBM absorption bands in the photocurrent spectrum. Time-resolved photoluminescence revealed the emission band at 2.10 eV with a fast decay time of 7 ps, and the more stable band at 1.88 eV. It was observed that PCBM caused quenching of the PAZ emission, what indicates the energy transfer from PAZ to PCBM.

PL

W niniejszej pracy przedstawiamy właściwości optyczne otrzymanej poliazometiny 25Th-cardo i jej mieszaniny z estrem [6,6]-fenylo-metylowym-C61 kwasu masłowego (PCBM). Dla polimeru obserwujemy znaczącą absorpcję dla długości fal krótszych niż 480 nm (2,6 eV). Zewnętrzna wydajność kwantowa ogniw słonecznych na bazie 25Th-cardo:PCBM była najwyższa (około 0,3%) w zakresie bliskiego UV. Obliczenia teoretyczne pokazują, że energie poziomów HOMO są równe -6,0 eV i -5,99 eV, odpowiednio dla 25Th-cardo i PCBM. Tak mała różnica energii umożliwia wyciekanie dziur z 25Th-cardo do PCBM, co może tłumaczyć niską wydajność ogniw oraz obecność pasm absorpcyjnych PCBM w widmie fotoprądu. Fotoluminescencja czasowo-rozdzielcza daje pasmo emisji dla energii 2,10 Ev o szybkim czasie zaniku (7 ps) oraz bardziej stabilne pasmo przy 1,88 eV. Stwierdzono, że dodatek PCBM powoduje stłumienie emisji 25Th-cardo, co wskazuje na przenoszenie energii z 25Th-cardo do PCBM.

3

Exciton localization behaviour in different well width undoped GaN/Al₀.₀₇Ga₀.₉₃N nanostructures

Sabooni M., Esmaeili M., Haratizadeh H., Monemar B., Paskov P., Kamiyama S., Iwaya M., Amano H., Akasaki I.

Opto-Electronics Review

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2007

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Vol. 15, No. 3

163-167

EN

We report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al₀.₀₇Ga₀.₉₃N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the "S-shape" dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.

4

AlGaN and InAlGaN alloys : epitaxial growth optical and electrical properties, and applications

Jiang H. X., Lin J. Y.

Opto-Electronics Review

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2002

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Vol. 10, No. 4

271-286

EN

The paper summarises some of recent advances made by the author's group on the growth, characterization and applications of AlGaN and InAlGaN alloys. Electrical, optical as well as optoelectronic properties have been studied. It is shown that the effect of carrier localisation in undoped AlGaN alloys enhances with increased Al contents and is related to the insulating nature of AlGaN of high Al contents. Si-doping reduces the effect of carrier localization in AlGaN alloys and a sharp increase in conductivity occurs when the Si doping concentration increases to above 10¹⁸ cm⁻³. For the Mg- doped Alx Ga₁-xN alloys, p-type conduction was achieved for x up to 0.27. Due to the strong piezoelectric polarization and deep triangular potential notch in AlxGa₁-xN (x=0.5) heterointerface, a total of five emission lines related with the two-dimensional electron gas in heterostructure have been observed, which correspond to the recombination between the electrons from different sub-bands. The dominant optical transition at low temperatures in Inx AlyGa₁-xN quaternary alloys is due to localized exciton recombination, while the localisation effects were combined from those of InGaN and AlGaN ternary alloys with comparable In and Al compositions. Finally micro-size ultraviolet light emitters are demonstrated.