Selective Area Growth of III-Nitrides on Polar and Semi-Polar Orientations: from Light Emitters to Pseudo-Substrates

摘要

New advances on Selective Area Growth (SAG) of InGaN/GaN nanostructures by plasma-assisted MBE on GaN/sapphire templates and Si (111) substrates are presented. Both, axial and core-shell structures are considered. Very intense green electroluminescence (figure 1) is achieved on axial nanoLEDs grown on Si(111) with very little peak drift and droop effects with current injection. First results on core-shell InGaN/GaN structures grown by MBE on GaN templates are also presented (figure 2). Cylindrical micro-rods are etched down by ICP from a 3 micron thick GaN/sapphire template. GaN and InGaN layers are then grown both in axial and radial directions so that the initial GaN cylinder is covered in a conformal way. Hexagonal symmetry is fully recovered once the GaN shell layer is grown. Potential advantages of this core-shell structure as compared to the axial one are twofold: the increase of emission surface (lateral area) and the absence of internal electric fields (m-plane). The crystal perfection is much better than that of 2D InGaN films of similar In% composition. Ordered arrays of GaN and InGaN axial nanostructures are grown on non-polar and semi-polar directions and subsequently merged into a continuous film to produce high quality pseudo substrates. Results show that in both cases the resulting films exhibit a very strong luminescence, orders of magnitude higher that from the substrate used. Semi-polar GaN templates have a huge density of stacking faults (SFs) most of them are filtered upon coalescence of the nanostructures grown on top. In all cases there is a preferential growth direction along the c-plane (0001). PL and spatially resolved CL measurements on individual nanostructures, either polar, non-polar, or semi-polar show that the In% incorporation depends strongly on the crystal plane considered.