Effects of Pre-Metallization on the MOCVD Growth and Properties of Ge-doped AlGaN on AlN/Sapphire Templates

The effects of pre-metallization of the growth surface on film stress and structural properties of undoped and Ge-doped AlxGa1-xN (x similar to 0.5-0.6) epilayers grown by metal-organic chemical vapor deposition (MOCVD) on 500 nm-thick hydride vapor-phase epitaxy (HVPE) AlN/sapphire templates were investigated. AlxGa1-xN typically grows under compressive stress on the AlN templates due to its larger lattice parameter, which can lead to increased surface roughness and V-pits in undoped and Ge-doped AlxGa1-xN. The introduction of the group III sources in the growth ambient for a short period of time (5 s) prior to the addition of NH3 induced a tensile growth stress in the AlxGa1-xN, as measured by in situ wafer curvature measurements, which correlated with an improvement in the surface morphology. However, the pre-metallization was also observed to result in the deposition of a carbon-rich layer at the AlxGa1-xN/AlN interface and an increased density of screw-type dislocations as measured by post-growth x-ray diffraction. By utilizing a pre-metallization step with a lower AlxGa1-xN growth rate, it was possible to eliminate the carbon interfacial layer and maintain low surface v-pitting and threading dislocation density in Ge-doped AlxGa1-xN. The results provide insight into the impact of pre-metallization on the AlxGa1-xN/AlN interface and the structural properties of the layers.

Automated summary

The effects of pre-metallization on film stress and structural properties of undoped and Ge-doped AlxGa1-xN epilayers were investigated on AlN/sapphire templates. Pre-metallization induced a tensile growth stress in the AlxGa1-xN and improved the surface morphology, but also led to the deposition of a carbon-rich layer and increased density of screw-type dislocations. However, by adjusting the AlxGa1-xN growth rate during pre-metallization, the carbon interfacial layer could be eliminated and low surface v-pitting and threading dislocation density in Ge-doped AlxGa1-xN could be maintained.