SINOPLE

Surface engineered InGaN heterostructures on N-polar and nonpolar GaN-substrates for green light emitters

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 Obiettivo del progetto (Objective)

'The goal of this project is to develop the potential of molecular beam epitaxy on nearly dislocation free GaN single crystals for semiconductor lasers in the green spectral range (520-550nm). The active structure will consist of In-rich InGaN layers. Our goal is to push the internal quantum efficiencies of green emitting InGaN devices at 520 nm beyond 30% and to obtain stimulated emission beyond 500 nm. This will be done by (i) engineering the active structure of the device to reduce the effects of piezeolectric fields that reduce the efficiency of these devices (ii) exploring molecular beam epitaxy on non-polar, semi polar and N-polar surfaces to obtain maximum In incorporation and by (iii) improving the structural perfection of the active layers by applying surfactants. It must be understood though that there is no fully established know-how, in terms of growth, optical and structural properties of In-rich InGaN/GaN heterostructures Spinodal decomposition, In-segregation and misfit dislocation formation are still major issues. Structural degradation caused by the specific growth conditions necessary for high In-content layers dramatically reduces the internal quantum efficiency. Piezoelectric fields, due to the high strain of In-rich structures contribute to further reduction in efficiency of devices. Realisation of nonpolar or semipolar devices can reduce the piezoelectric fields. However, high levels of In incorporation, a prerequisite for green emitters, is a challenge that has not been solved till now. Our project combines molecular-beam epitaxy with unique dislocation free GaN substrates, advanced structural analysis and state of the art modelling and simulation to overcome these limitations. The project will take full advantage of the know-how acquired at TopGaN in the growth of UV lasers by MBE and the progress made in dislocation free substrates. This will enable growth to be performed on any defined surface orientation required.'

Introduzione (Teaser)

Lasers emitting green light currently have limited efficiencies, power and lifetimes. EU-funded scientists have made important progress towards novel technology that could change that in the near future.

Descrizione progetto (Article)

The crystalline semiconductor gallium nitride (GaN) has opened the door to realize green lasers thanks to its unique optoelectronic properties. Indium GaN (InGaN) devices operating in the green spectral range region (wavelengths around 510 to 570 nm) are the result. However, despite recent progress, high-quality InGaN light-emitting and laser diodes (LEDs) are very difficult to produce.

EU-funded scientists tackled the technical basis for the deficiencies through the project http://www.sinople-iapp.eu/ (SINOPLE). The team focused on the use of molecular beam epitaxy (MBE) to deposit In-rich InGaN active layers onto nearly dislocation-free GaN single crystals. Incorporating high levels of In, a prerequisite for the green emitters, had not been achieved previously by MBE and there was no detailed knowledge of In-rich InGaN/GaN heterostructures.

Researchers achieved epitaxial growth of InGaN with high In content (up to 20 %) on various substrates using MBE. Scientists also had success exploiting InGaN on zinc oxide. On the road to device development, the team also produced a highly sensitive method to characterise In fluctuation based on transmission electron microscopy with unprecedented accuracy.

Investigators delivered a variety of lasers in the ultraviolet, blue and green spectral ranges. The novel MBE system facilitated growth of higher-quality InGaN and produced a record for electrically pumped nitride MBE laser diodes with wavelength emission at 482 nm.

Additionally, the team produced continuous-wave laser diodes with a wavelength of 450 nm, a power of 60 mW and a lifetime exceeding 5 000 h. The result shows that MBE can compete with conventional metal organic chemical vapour deposition (MOCVD). In addition, the technique facilitates flexibility in processing temperature and substrates that are not accessible with MOCVD.

SINOPLE has significantly advanced the state of the art regarding production of green LED lasers with higher efficiencies, power and lifetimes. The application potential is enormous for this elusive coherent-light source. From information displays to televisions to biomedicine, the world is on the brink of an eye-opening surprise.