Reduction of threading defects in GaN grown on vicinal SiC(0001) by molecular-beam epitaxy

Abstract

We observe a significant reduction of threading dislocations in GaN grown on vicinal substrates of SiC͑0001͒. Using scanning tunneling microscopy, we find films grown on vicinal substrates maintain the surface misorientation of the substrate and display terraces with straight edges. On top of the terraces there is no spiral mound, which is the main feature found for films grown on singular substrates. Transmission electron microscopy studies confirm that threading screw dislocations are reduced by two orders of magnitude while edge dislocations are reduced by one order.

Structural Properties of GaN Films Grown by Molecular Beam Epitaxy on Singular and Vicinal 6H-SiC(0001)

“…TEM measurements have not been performed to date, so no further information in available concerning the mechanism for dislocation reduction in these films. Recently Xie et al [6] have reported results for dislocation reduction in GaN films grown on vicinal SiC. In their case the initial SiC substrates were not H-etched, so that their screw dislocation density for growth on singular substrates was very high.…”

“…Most growth has been performed on singular (no intentional miscut, or on-axis) (0001) Si-face substrates, although a few studies have employed vicinal (miscut, or off-axis) substrates. One report in particular, by Xie et al [6], has reported significantly improved film quality on the vicinal substrates, as discussed in more detail below.…”

“…A number of research groups have in recent years studied the growth using molecular beam epitaxy (MBE) of GaN on SiC [1][2][3][4][5][6][7]. Hydrogen etching of the substrates is becoming a standard preparation step for removing polishing damage [8].…”

Structural anisotropy in GaN films grown on vicinal 4H-SiC surfaces by metallorganic molecular-beam epitaxy

“…An early coalescence due to a higher nucleation density and preferential coalescence along step edges was found to substantially improve the GaN crystal quality of the film grown on the vicinal SiC surface. 17 …”

“…In both cases the majority of defects is a threading dislocations, which are introduced when two nuclei coalesce. [15][16][17] If the nuclei are incoherent and, in most cases, probably also twisted/tilted with respect to each other due to a mismatch relaxation process, the edge-type dislocation having a Burgers vector parallel to the basal plane is generated at the boundary to compensate incoherent lattices. The plan-view TEM study on GaN nuclei on SiC surfaces indicates a wandering feature of moiré fringes and the presence of dislocations as a result of incoherent nature of GaN nuclei.…”