Al0.31Ga0.69N/AlN/GaN/InxGa1-xN/GaN heterostructures grown with the metal-organic chemical vapor deposition (MOCVD) technique with different InxGa1-xN back-barriers with In mole fractions of 0.05 <= x <= 0.14 were investigated by using XRD measurements. Screw, edge, and total dislocations, In mole fraction of back-barriers, Al mole fraction, and the thicknesses of front-barriers and lattice parameters were calculated. Mixed state dislocations with both edge and screw type dislocations were observed. The effects of the In mole fraction difference in the back-barrier and the effect of the thickness of front-barrier on crystal quality are discussed. With the increasing In mole fraction, an increasing dislocation trend is observed that may be due to the growth temperature difference between ultrathin InxGa1-xN back-barrier and the surrounding layers. (C) 2012 Elsevier B.V. All rights reserved.