High‐Temperature Annealing and Patterned AlN/Sapphire Interfaces

Abstract

Using the example of epitaxial lateral overgrowth of AlN on trench-patterned AlN/sapphire templates, the impact of introducing a high-temperature annealing step into the process chain is investigated. Covering the open surfaces of sapphire trench sidewalls with a thin layer of AlN is found to be necessary to preserve the trench shape during annealing. Both the influence of annealing temperature and annealing duration are investigated. To avoid the deformation of the AlN/sapphire interface during annealing, the annealing duration or annealing temperature must be low enough. Annealing for 1 h at 1730 C is found to allow for the lowest threading dislocation density of 3.5 Â 10 8 cm À2 in the subsequently grown AlN, while maintaining an uncracked smooth surface over the entire 2 in. wafer. Transmission electron microscopy study confirms the defect reduction by high-temperature annealing and reveals an additional strain relaxation mechanism by accumulation of horizontal dislocation lines at the interface between annealed and nonannealed AlN. By applying a second annealing step, the dislocation density can be further reduced to 2.5 Â 10 8 cm À2 .

Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers

“…This layer was patterned into stripes along the [1-100] direction of AlN by standard lithography and ICP etching. The patterned template was subsequently overgrown with 5 μm thick AlN layers at temperatures of around 1180-1250 C. [30] NaOH/KOH and Ba(OH) 2 were first mixed with 10% MgO powder, respectively, and subsequently homogenized by melting in a nickel crucible at about 450 C. After cooling, a spatula tip of the resulting solid was placed on the surface of the cold sample. The etching process was started by placing the sample with solid etchant on the preheated heating plate and ended after 30 s by removing it again from the hot plate.…”

“…The patterned template was subsequently overgrown with 5 μm thick AlN layers at temperatures of around 1180–1250 °C. [ 30 ]…”

Progress on photovoltaic AlGaN photodiodes for solar-blind ultraviolet photodetection

“…Therefore, it is important that the annealing duration or temperature must be low enough. Several two-step approaches were reported for solving the problems [58][59][60] . For example, Hagedorn et al found that AlN epitaxial films were formed at 1250°C via using MOVPE and then annealed at 1730°C for 1 h, which not only stabilized the AlN/sapphire interface but also reduced TDD during annealing [58] .…”

“…Several two-step approaches were reported for solving the problems [58][59][60] . For example, Hagedorn et al found that AlN epitaxial films were formed at 1250°C via using MOVPE and then annealed at 1730°C for 1 h, which not only stabilized the AlN/sapphire interface but also reduced TDD during annealing [58] . Then, the AlN films subsequently were annealed at 1690°C for 3 h to further reduce TDD.…”

Radiative Recombination and Carrier Injection Efficiencies in 265 nm Deep Ultraviolet Light‐Emitting Diodes Grown on AlN/Sapphire Templates with Different Defect Densities

“…[36,40] As a consequence, misfit dislocations can be introduced in the AlN and AlGaN layers by the formation of dislocation half-loops (DHLs). [36,40,41] The DHLs have an in-plane misfit component with one TD aligned in the growth direction on each side, as shown in Figure 5. By interacting with each other, the threading components of the individual halfloops can annihilate and form DHLs of an irregular shape.…”