Design of the low-temperature AlN interlayer for GaN grown on Si (1Â 1Â 1) substrate

We have investigated the effect of the thickness and layer number of the low-temperature AlN interlayer (LT-AlN IL) on the stress relaxation and the crystal quality of GaN epilayers grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition. It is found that the stress decreases with the increase of the LT-AlN IL thickness, but the crystal quality of the GaN epilayer goes worse quickly when the LT-AlN IL thickness is larger than 16 nm. This is because the increase of the LT-AlN IL thickness will increase the coalescence thickness of its upper GaN layer, which sensitively affects the crystal quality of the epilayer. Using multiple LT-AlN ILs is an effective method not only to reduce the stress, but also to improve the crystal quality of the GaN epilayer. With the increase of the interlayer number, the probability that dislocations are blocked increases and the probability that dislocations are produced at interfaces decreases. Thus, dislocations in the most upper part of GaN are reduced, resulting in the improvement of the crystal quality. Finally, it is suggested that when the total thickness of the epilayer is fixed, both the thickness and the number of the LT-AlN IL should be carefully designed to reduce the stress and improve the crystal quality of the epilayer simultaneously.