Influence of substrate nitridation on GaN and InN growth by plasma-assisted molecular-beam epitaxy

Abstract

The influences of sapphire (Al₂O₃) substrate nitridation on the growth of GaN and InN by plasma-assisted molecular-beam epitaxy (PAMBE) were studied by using reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction (XRD). Three factors have been investigated, including (1) the effect of ionic nitrogen species; (2) nitridation time; and (3) substrate temperature (T_s). RHEED and AFM results have suggested that although AlN formation on sapphire during nitridation is faster when ionic nitrogen species are present or when T_s is higher, the resultant AlN layer is not as homogeneous as that formed without ionic nitrogen species and/or at lower T_s. An inhomogeneous AlN coverage on sapphire leads to GaN and InN growth with more defects, especially to a serious twist misorientation in the case of InN. Optimal nitridation conditions in this experiment have been found to be applying ion-free nitrogen species at T_s = 300°C for a duration about 300 min.