Growth Mechanism and Strain Variation of GaN Material Grown on Patterned Sapphire Substrates With Various Pattern Designs

Growth mechanism and strain variation of GaN material grown on patterned sapphire substrates (PSS) with various pattern designs are investigated. Time evolutions of GaN epi-layer grown on trapezoid-shaped PSS (TPSS) and cone-shaped PSS (CPSS) are demonstrated by field emission scanning electron microscopy (SEM). From the transmission electron microscopy (TEM) observations, the threading dislocations (TDs) of CPSS is less than that of TPSS. Space-depended strain in GaN epi-layer grown on PSS is measured by micro-Raman spectroscopy. The magnitude of residual strain of 6-μm-period TPSS is Δσ ≈ 0.97 GPa and that of 6-μm -period CPSS is Δσ ≈ 0.17 GPa. On the other hand, a design of shorter period (3-μm-period PSS) could further release residual strain of epitaxial GaN thin film. Based on experimental results, it is suggested that the CPSS with short period has better epitaxial quality and less residual strain than TPSS.