Demonstrating the Effects of Growth Temperatures of Al(In)GaN Back Barrier on Transport Properties of InAlGaN/GaN Heterostructures

The growth and optimization of Al(In)GaN back barrier by MOCVD for InAlGaN-based heterostructures is successfully demonstrated. At zero growth temperature gap (which was defined by ΔT g = ∣T g , channel -T g , BB ∣), the coherent growth of the back barrier was confirmed by perfectly ordered atoms, sharp interface quality, and absence of threading dislocations at the buffer/back-barrier/channel interfaces, including the smoothest surface of heterostructures. The electron transport properties of InAlGaN/GaN heterostructures were consistently affected by the growth temperature of the back barrier. Significant increase of electron mobility from 1560 to 1740 (cm 2 Vs −1 ) and decrease of sheet carrier density from 1.57 × 10 13 to 1.31 × 10 13 (cm −2 ) were attributed to the improvement of electron confinement by adapting a thin ( 3.5 nm) optimized Al(In)GaN back barrier to the conventional InAlGaN/GaN heterostructure. XPS chemical shifts of the N1s core level and band alignment calculation have also confirmed the influence of the growth temperature of the back barrier on the electron confinement. Moreover, a large positive shift of the threshold voltage (2 V), a considerable increase in maximum transconductance from 180 to 216 (mS mm −1 ), and suppression of the Kink effect of the devices were realized, which paves the way for the employment of the Al(In)GaN back barrier for high-frequency applications.