We present results of our studies dealing with the early stages of growth of Ga-N and Al-N monolayers on the 4H-SiC {0001} substrates. These studies are based on first principles calculation in the framework of density functional theory. Some stable adsorption sites are found for Ga, N, and Al atoms on the 4H-SiC {0001} surfaces. These are in particular T-4 for Ga and N atoms adsorbed on the (0001) surface and on top of the topmost surface atom for Al at the 1 ML coverage. In the case of (000 (1) over bar) surface, it is the 'on-top' position for Ga and Al, as well as T-4 for N atoms, at the same coverage. Further, the energetics of the GaN and AlN monolayers formation on the SiC substrate is investigated. It can be stated that the best 4H-SiC substrate termination allowing the single unreconstructed GaN bilayer growth is the (0001) one Possible charge compensation patterns of interfaces are proposed together with the discussion on their stability. They involve the mixed Ga-C/SiC{0001} or Ga-Si/SiC{0001} layers that in consequence lead to the adsorption energy gain for nitrogen. (C) 2014 Elsevier B.V. All rights reserved.