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.
Field of science
- /natural sciences/physical sciences/optics/laser physics
Call for proposal
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