Embodiments of the present disclosure include a buffer structure suited for III-N device having a foreign substrate. The buffer structure can include a first buffer layer having a first aluminum composition and a second buffer layer formed on the first buffer layer, the second buffer layer having a second aluminum composition. The buffer structure further includes a third buffer layer formed on the second buffer layer at a second interface, the third buffer layer having a third aluminum composition. The first aluminum composition decreases in the first buffer layer towards the interface and the second aluminum composition throughout the second buffer layer is greater than the first aluminum composition at the interface.