High quality lnxGa1-xN thin films with x> 0.2 grown on silicon

Using plasma-assisted molecular beam epitaxy (PA-MBE), high quality In x Ga 1-x N layers with x in the range from 25 to 31% have been grown on silicon (111) substrates. The polarity of the layers has been found to impact the incorporation of In, with Ga polar buffers promoting the deposition of uniform composition InGaN. We have achieved films with indium fraction up to 31 % and rocking curve width of 538 arcsec. Residual donor concentration as low as ∼ 1.2 × 10 18 cm -3 was measure in these films, suggesting that p-type doping with Mg can be achieved. The presence of AlN layers and the increasing thickness of the GaN buffer do not appear to have a significant contribution to the series resistance of the structure. The investigation of the InGaN layers by X-ray diffraction did not reveal any significant phase separation occurring during the MBE deposition although the photoluminescence spectrum exhibits low energy features that would require further investigation.