Strain-reduced GaN thick-film grown by hydride vapor phase epitaxy utilizing dot air-bridged structure

A 300 μm GaN thick-film, in diameter 1.5 in, was demonstrated without any crack by hydride vapor phase epitaxy (HVPE) growth. The technique used in relaxing the residual stress caused by differences of thermal expansion coefficients (TEC) and lattice constants between GaN and sapphire substrate to prevent GaN film from crack is called a dot air-bridged structure. After the laser lift-off process, 300-μm-thick freestanding GaN wafer, in diameter 1.5 in, could be fabricated. The compressive stress in the dot air-bridged structure was measured by micro-Raman spectroscopy with the E₂(high) phonon mode. The compressive stress could be reduced to as small as 0.04 GPa, which could prevent the crack during the epitaxial process for GaN growth by HVPE. It is important to obtain a large-area crack-free GaN thick-film, which can be used for fabricating freestanding GaN wafer.