Effect of Growth Temperature on Strain during Growth and Crack Suppression in AlGaN Templates on Sapphire Substrates for Deep Ultraviolet Light‐Emitting Diodes

The crack formations in AlGaN templates for deep ultraviolet (DUV) light‐emitting diodes (LEDs) are investigated and successfully suppressed. The strain values in AlGaN thick layers on sapphire substrates by in situ wafer curvature measurements and ex situ X‐ray diffraction measurements are evaluated. It is found that the tensile strain during the AlGaN thick layer growth comes from a thermal expansion difference between the AlGaN thick layer and the sapphire substrate as the temperature changes from the AlN nucleation layer growth to the AlGaN thick layer growth. When the temperature change is 100 °C and less, the tensile strain of 0.1% and less is observed during the AlGaN thick layer growth, resulting in no crack formations in the AlGaN thick layer. Furthermore, a DUV LED layer structure grown on such a crack‐free AlGaN template shows no crack formations. Thus, to suppress crack formation in templates fabricated for DUV LEDs, their growth temperature must be optimized by considering thermal expansions caused by the changes in the growth temperature from the nucleation layer to the thick layer.