Crack-free GaN deposition on Si substrate with temperature-graded AlN buffer growth and the emission characteristics of overgrown InGaN/GaN quantum wells

• Use a temperature-graded AlN buffer for crack-free GaN growth on Si substrate.
• Show the emission behavior of InGaN/GaN QW with temperature-graded buffer.
• Weakest residual stress corresponds to the highest internal quantum efficiency.

The technique of depositing a temperature-graded AlN buffer layer for crack-free GaN growth on Si substrate is demonstrated. Compared with the previously reported methods of buffer growth, this technique has the advantages of a thinner buffer layer for effectively producing compressive stress and simple binary growth without the need of changing its composition. By combining with an inter-layer structure of three-period GaN/AlN superlattice, crack-free growth of thick GaN layers of 3.7 μm in total thickness is implemented. Also, the different emission behaviors of overgrown InGaN/GaN quantum wells (QWs) under different stress conditions with different graded temperature numbers are illustrated. It is found that the QW sample with the highest graded temperature number for depositing the AlN buffer has the weakest residual tensile stress, the shortest emission wavelength, the weakest carrier localization effect, the weakest quantum-confined Stark effect, and the highest internal quantum efficiency, even though the total indium content is about the same as those of other samples with significantly stronger residual stresses.