The group III nitrides of AlN, GaN and InN possess direct bandgaps of ≒ 1.8eV ≒ 3.4eV$ and ≒ 6.2eV$, respectively. These compounds and their alloys have become key materials in the development and the commercial realization of short-wavelength photonic devices for display and data-storage applications, solar-blind UV detectors, as well as sources of white light. Essentially, all III-nitride films are heteroepitaxially grown on sapphire (α-Al2O3(0001)) or silicon carbide (SiC(0001)). These substrates have lattice parameters and coefficient of thermal expansion that are, respectively, +16% and +39% (sapphire) and -3.5% and -3.2%(SiC), Relative to GaN. The resulting residual stresses are accommodated by the formation of misfit and threading dislocations in the nitride layers. The latter dislocations occur throughout thin GaN films in densities of ≒109cm-2. These dislocations propagate up to the surface, deteriorating the performance of optical and electronic devices. Therefore, a primary goal in recent III-nitride research has been the reduction in the density of these defects.
In this paper, Maskless Pendeo Epitaxy that employs lateral growth from etched seed forms to achieve a marked reduction in dislocation in dislocation density in a material was investigated. For analysis, Pendeo Epitaxy GaN was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) for structural and optical properties of GaN layer. The crystallographic tilt and surface morphology in maskless Pendeo Epitaxy process is strongly related to the ratio of lateral to vertical growth rate (γ). Because γ is related to growth parameters such as growth temperature, reactor pressure and V/III ratio, Pendeo Epitaxy GaN with different growth parameters was systematically investigated.
The tilt at wing region is increased with relatively low γ but decreased with high γ. However extremely high γ rather tends to cause the degradation of surface morphology. Two-step growth process has been used for lower dislocation density in Pendeo Epitaxy GaN; the first-step has inclined facets, and then in the second step Pendeo Epitaxy GaN is easily buried by changing the growth conditions. In two step growth, the dislocation density is dramatically dropped.
