脉冲缓冲层对AlN外延层位错密度的影响

Effect of Pluse Buffer Layer on AlN Epilayer Dislocation Density

在蓝宝石衬底上采用交替通Al源和NH3的方法生长的100周期的AlN作为缓冲层,随后外延生长AlN薄膜。X射线衍射结果表明AlN外延层中的位错密度大大降低。通过透射电镜观察位错在样品中的形貌,发现在缓冲层和外延层之间存在明显的界面。界面之上的位错通过形成位错环互相湮灭或者直接终断于界面,使得在外延层中大量减少。研究表明,位错环的形成是由于在外延层的生长过程中侧向生长速率增加导致位错在镜像力的作用下互相吸引造成的。而位错在界面处的终断则被认为是由于界面上下应变发生变化引起的。

The AlN epilayer was grown on sapphire substrate with the introduction of a pulsed atomic-layer epiraxial(PALE)AlN buffer layer.Threading dislocations(TDs)densities in AlN epilayer were shown to be greatly decreased.From transmission electron microscopic images,a clear subinterface was observed between the buffer layer the subsequently continuous grown AlN epilayer.In the vicinity of the subinterface,the redirection,annihilation,and termination of TDs were observed.It is found that the redirection and annihilation of TDs are attributed to the increase in lateral growth rate.The strain variation between the two regions results in the termination of TDs owing to the dislocation line energy minimization.