LP MOVPE growth and characterization of high Al content Al xGa 1−xN epilayers

Abstract

High quality Al x Ga 1− x N layers have been grown on sapphire (0 0 0 1) by low pressure metalorganic vapour phase epitaxy (LP MOVPE) at 1180 °C. The aluminum content covers a wide composition range varying from 0 to 65%. In order to ameliore the quality of these epilayers especially for high aluminum content ( X s Al >0.35), growth conditions are carefully optimized. The growth rate of AlGaN increases linearly with increasing group III elements partial pressure. The reduction of the growth pressure from 50 to 20×10 −3 atm induces an increase of the growth rate and raises the solid Al content from 19.6 to 53.3%. Additionally, a linear relationship (slope about 1) is observed between gas and solid aluminum content in the whole range of Al content in AlGaN alloys grown at 20×10 −3 atm. The structural properties of Al x Ga 1− x N layers, with different aluminum composition, are characterized by double X-ray diffraction (DDX) showing a high quality of our epilayers. A degradation of the crystalline quality of Al x Ga 1− x N films is observed with increasing aluminum content. The optical properties of these layers are investigated by photoluminescence measurements at low temperature (12 K). With increasing the Al content, the principal peak (neutral donor bound exciton) shifts to higher energies and the full width at half maximum (FWHM) increases significantly.