Microstructures of GaN islands on a stepped sapphire surface

Abstract

We investigated the structural evolution of GaN nucleation layers in the initial growth stages on commercial c-plane sapphires with atomic steps at the surface, using field-emission scanning electron microscopy, synchrotron x-ray scattering, and high-resolution electron microscopy. GaN nucleates into islands preferentially on the atomic steps. The initial small islands of 25 Å high have well-ordered cubic sequences and nearly coherent interfacial structures with a large compressive strain of ∼10%. As the islands grow to 50 Å high, the strain is drastically reduced, to less than 1%, by generating misfit dislocations at the interface and forming the six-to-seven matched interfacial structure. Interestingly, stacking faults are developed from the GaN/sapphire interface, which induces a cubic–hexagonal transformation. The changes in the stacking order during the initial growth are investigated quantitatively.

Morphology of ZnO grown by MOCVD on sapphire substrates

“…The true misorientation angle of the global surface with respect to the terrace plane can be estimated from the ratio between terrace width and step height. This angle ranges between 0.06 (r-plane) and 0.1 (c-plane), values which are similar to those observed by Kim et al [26] (i.e., well within manufacturing specifications). Interestingly, and contrary to a-, c-and r-planes, substrates with mplane orientation showed atomically flat surfaces without visible atomic steps.…”

“…Due to the presence of steps on the initial surface, the ZnO dots, surprisingly homogeneous in size, nucleate forming lines periodically distributed over the entire surface. Very similar structures were observed in the first stages of growth of GaN on c-plane sapphire [26]. Fig.…”

Rietveld refinement for indium nitride in the 105–295 K range

“…Therefore, detailed studies of InN thermal expansion may be useful in designing and improving the technologies involving this material as a component. It has been reported that heteroepitaxial growth of wurtzitetype GaN or InGaN starts through growth of zincblende islands; this phenomenon can be observed in situ ͑see, e.g., Wu et al, 1996;Li et al, 1998;Kim et al, 2002͒. It clearly shows that for any III-V nitride, the elastic properties of both, zincblende and wurtzite, polytypes have to be studied.…”

Control of initial bow of sapphire substrates for III-nitride epitaxy by internally focused laser processing

“…Lu et al [9] also verified the importance of the wafer carrier design, and good uniformity was reported by accommodating the pocket shape to be the same as the bowing of the sapphire substrate during the InGaN growth stage for diameters up to 200 mm. In addition to the approach using thicker substrates and pocket shape accommodation, epitaxy process optimization, such as modifying the nucleation layer, controlling the coalescence stage, and inserting straincompensation layers, has been reported to reduce the strain and related substrate bowing both during and after epitaxy [10,[13][14][15][16][17][18][19][20][21][22][23]. However, all of the above approaches have consequently presented us with complicated epitaxy processing and MOCVD design engineering, leading to a cost expansion.…”