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3 Optica Applicata

3 2006

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Photoluminescence spectroscopy for the evaluation of band potential roughness of InGaN active layers

Kazlauskas K., Jursenas S., Miasojedovas S., Pobedinskas P., Tamulaitis G., Zukauskas A., Ivanov V.Y., Godlewski M.

Optica Applicata

2006

Vol. 36, nr 2-3

181-185

Photoluminescence spectroscopy in combination with Monte Carlo simulation of exciton hopping is demonstrated to be a valuable tool for quantitative analysis of the band potential profile in active layers for InGaN-based light emitters. Recently proposed double-scaled potential profile model is used to reveal the scale of potential fluctuations in the individual In-rich regions as well as the dispersion of the average exciton localization energy in these regions. The influence of the different potential fluctuation scales on the stimulated emission threshold and luminescence decay time of highly excited InGaN active layers is studied.

Fluorescence detection of biological objects with ultraviolet and visible light-emitting diodes

Kurilcik N., Vitta P., Zukauskas A., Gaska R., Ramanavicius A., Kausaite A., Jursenas S.

Optica Applicata

2006

Vol. 36, nr 2-3

193-198

Recent progress in fabrication of semiconductor light emitting diodes (LEDs) allows these devices to be used for excitation of fluorescence of aromatic amino acids and other biofluorophores. In our work, a deep-UV UVTOPTM LED (280 nm) developed by Sensor Electronic Technology, Inc., was used for fluorescence characterisation of natural protein fluorophores in enzyme glucose oxidase (GOx) and in Bacillus subtilus dry spores (B. subtilus). A longer-wavelength Nichia LED (375 nm) and high-power LuxeonTM LED (450 nm) were used for fluorescence detection of enzyme cofactors. Combined spectral and fluorescence lifetime measurements using selective LED excitation enabled us to recognise the impact of specific autofluorophores in complex biological systems. Inexpensive LED-based fluorescence detectors can be used in designing biosensors and detect-to-warn systems.

Characterization of InGaN structures grown by epitaxial lateral overgrowth over a-plane GaN template

Miasojedovas S., Jursenas S., Kuokstis E., Zukauskas A., Gaevski M.E., Lee J., Shatalov M., Gong Z., Adivarahan V., Sattu A., Mokina I., Yang J., Asif Khan M.

Optica Applicata

2006

Vol. 36, nr 2-3

351-358

We report on the luminescence characterization of InGaN/GaN multiple quantum well (MQW) structures with average 15% In content in the well layers, grown on polar and non-polar sapphire substrates utilizing epitaxial lateral overgrowth (ELOG) technique. Significant modification of the emission properties of MQWs grown over non-polar ELOG structure in comparison with non-polar orientation was observed. It was attributed to the formation of In-rich quantum dot like structures in the vicinity of substrate related defects along stripes formed during ELOG procedure. The absence of the stimulated emission and the significant reduction of carrier lifetime, observed under strong excitation, indicate the high density of nonradiative centers in the In-rich quantum dot regions of non-polar ELOG MQWs.