The band-gap bowing of AlxGa1−xN alloys

The band gap of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ is measured for the composition range $\text{0⩽x<0.45;}$ the resulting bowing parameter, $\text{b=+0.69\hspace{0.05em}}\mathrm{eV},$ is compared to 20 previous works. A correlation is found between the measured band gaps and the methods used for epitaxial growth of the ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}:$ directly nucleated or buffered growths of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ initiated on sapphire at temperatures $\text{T>800\hspace{0.05em}°}\mathrm{C}$ usually lead to stronger apparent bowing $\text{(b>+1.3\hspace{0.05em}}\mathrm{eV}\mathrm{);}$ while growths initiated using low-temperature buffers on sapphire, followed by high-temperature growth, lead to weaker bowing $\text{(b<+1.3\hspace{0.05em}}\mathrm{eV}\mathrm{).}$ Extant data suggest that the intrinsic band-gap bowing parameter for AlGaN alloys is $\text{b=+0.62(±0.45)\hspace{0.05em}}\mathrm{eV}.$