Paper presents the comparative analysis of Metal Modulated Epitaxy (MME) and Droplet Elimination by Thermal Annealing (DETA) techniques in the low-temperature plasma-assisted MBE of thick AlxGa1-xN layers with the medium Al content (x=0.4-0.6) grown under the highly metal-rich conditions. Atomically smooth surface with RMS of about 0.4 nm across the area of 2 x 2 mu m(2) has been achieved for AlGaN layers grown at F-III/F-N flux ratio of 25 and substrate temperature of 700 degrees C by using DETA. The MME growth of AlGaN epilayers leads to their cracking due to the tensile stress introduced by relaxed GaN interlayers which are formed during the nitrogen exposure of the Ga-enriched AlGaN surface. A new technique based on IR-pyrometry measurements has been developed to monitor in situ metal accumulation and depletion on the growth surface. (C) 2015 Published by Elsevier B.V.