Growth defects in GaN films on sapphire: The probable origin of threading dislocations

Abstract

Single crystal GaN films with a wurtzite structure were grown on the basal plane of sapphire. A high density of threading dislocations parallel to the c-axis crossed the film from the interface to the film surface. They were found to have a predominantly edge character with a Burgers vector. In addition, dislocation hal-loops, elongated along the c-axis of GaN, were also found on the prism planes. These dislocations had a mostly screw character with a [0001] Burgers vector. Substrate surface steps with a height of were found to be accommodated by localized elastic bending of GaN (0001)GaN planes in the vicinity of the film/substrate interface. Observations show that the region of the film, with a thickness of ∼100 nm, adjacent to the interface is highly defective. This region is thought to correspond to the low-temperature GaN “buffer” layer which is initially grown on the sapphire substrate. Based on the experimental observations, a model for the formation of the majority threading dislocations in the film is proposed. The analysis of the results leads us to conclude that the film is under residual biaxial compression.

Initial Growth Prismatic Domains in Cyclotron Assisted MBE of GaN/SiC

“…They are mainly threading dislocations and planar defects. Dislocations are reported to have a, c, or a + c Burgers vector [2] [3] and to form low angle grain boundaries which result from the coalescence of islands [2]. Different kinds of planar defects have also been reported: stacking faults [4] parallel to the film/substrate interface, and planar faults perpendicular to the interface.…”

Crack-free thick AlGaN grown on sapphire using AlN/AlGaN superlattices for strain management

“…Usually, strain can be released by the creation of misfit dislocations. In III nitrides, because of the absence of an effective slip system, 15 dislocations are difficult to generate and glide. On the other hand, the development of biaxial tensile strain in AlGaN grown on c-face sapphire is not well understood.…”

Surface Treatment and Layer Structure in 2H-GaN Grown on the (0001)Si surface of 6H-SiC by MBE

“…The screw dislocations introduce systematically a rotation of each island about the (0001) growth directions [9], [10].…”