Modulated Ammonia Flow - Low Temperature AlN Buffer LP-MOVPE Growth for High Quality AlGaN Layers

The structural properties of AlGaN layers deposited on high- and low-temperature grown AlN buffer were analysed. Modulated ammonia flow method of preparing AlN buffer was compared with a constant ammonia flow process using metalorganic vapour phase epitaxy. Low-temperature growth of the AlN buffer led to an increase of surface roughness, nevertheless crystal quality was comparable to the AlN buffer grown in high-temperature. Low-temperature nucleation AlN on sapphire substrates was required due to differences in thermal expansion and possible reduction of the number of dislocation. Modulated ammonia flow method provides an alternative approach for the AlN buffer growth at reduced reactor temperature.