Andrea Pinos

Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy

Scanning near-field photoluminescence spectroscopy has been applied to evaluate bandgap fluctuations in epitaxial AlGaN films with the AlN molar fraction varying from 0.30 to 0.50. A dual localizat ...

High current-induced degradation of AlGaN ultraviolet light emitting diodes

Degradation under high current stress of AlGaN quantum well based light emitting diodes emitting at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence and current-voltage experimental techniques. The measurements have revealed that during aging decrease of the emission intensity is accompanied by increase of the tunneling current, increase of the nitrogen vacancy concentration and partial compensation of the p-doping. The main role in the device degradation has been ascribed to formation of tunneling conductivity channels, probably, via activation of the closed core screw dislocations with the help of nitrogen vacancies. Carrier lifetimes in the quantum wells and the p-cladding were found to be unaffected by the aging process, suggesting that the nonradiative recombination has a lesser influence on the device degradation.

Time-resolved luminescence studies of proton-implanted GaN

Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose of 1×1015 cm−2, decreases down to a few picoseconds. With annealing at temperatures between 250 and 750 °C, carrier lifetime, contrary to electrical characteristics, is only slightly restored, indicating that electrical compensation and carrier dynamics are governed by different defects. Ga vacancies, free and bound at threading dislocations, are suggested as the most probable defects, responsible for electrical compensation and carrier lifetime quenching.

Carrier localization in m-plane InGaN/GaN quantum wells probed by scanning near field optical spectroscopy

Scanning near field optical microscopy (SNOM) was applied to study the carrier localization in single InGaN/GaN quantum well structures grown on nonpolar m-plane GaN substrates. Dual localization p ...

Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy

Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas emitting with a higher intensity and at a longer wavelength; presumably, because of a lower AlN molar fraction in these regions. Experiments performed on different days have shown that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating a further change in the quantum well alloy composition. This has allowed distinguishing an aging mechanism that involves locally increased current, heating, and atom migration.

Screening dynamics of intrinsic electric field in AlGaN quantum wells

Shift of the transition energy after pulsed optical excitation in Al0.35Ga0.65N/Al0.49Ga0.51N quantum well (QW) structures with varying well width has been studied by time-resolved photoluminescenc ...

Optical studies of degradation of AlGaN quantum well based deep ultraviolet light emitting diodes

Aging under high current stress of AlGaN quantum well based light emitting diodes with high and low Al content in the wells emitting at 270 nm and 335 nm, respectively, has been studied by scanning near field optical spectroscopy and far field electroluminescence, photoluminescence and time-resolved photoluminescence. In the high Al content devices emission band related to optical transitions in the cladding involving nitrogen vacancies has been found. Evolution of this band during aging suggests that the role of N vacancies is crucial in the aging process by aiding defect generation and formation of high conductivity channels.

Carrier lifetimes in AlGaN quantum wells: electric field and excitonic effects

Photoexcited carrier dynamics in a 280 nm AlGaN quantum well (QW) light emitting diode has been studied by time-resolved photoluminescence at forward and reverse bias. Long (for AlGaN QWs with high Al content) room temperature carrier lifetimes of about 600 ps were measured with only a slight dependence on bias. These lifetimes are much longer than calculated free carrier tunnelling and thermionic emission times, pointing out the importance of excitonic effects for carrier dynamics in AlGaN QWs.

Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy

Time-resolved transmission and photoluminescence measurements were performed on Al0.35Ga0.65N/Al0.49Ga0.51N quantum well structures with different well widths. Comparison of transmission and lumine ...

Intrinsic electric fields in AlGaN quantum wells

Intrinsic electric fields in AlxGa1-xN/AlyGa1-yN quantum wells embedded into p-i-n structures are studied using photoluminescence experiments. Spectral shifts induced by external bias and screening ...