Effect of Graded AlxGa1-xN Layers on the Properties of GaN Grown on Patterned Si Substrates

2.2-µm-thick crack-free GaN films were grown on patterned Si substrates. The crack-free GaN films were obtained by patterning Si substrate and optimizing the graded Al x Ga1-x N layers. With the increase of the graded Al x Ga1-x N layer thickness, the GaN crystal quality improved as judged from the X-ray diffraction data. By applying multi-Al x Ga1-x N layers on the patterned Si substrate, a 31% reduction of tensile stress for the GaN film was obtained as measured by micro-Raman. For the AlGaN/GaN high electron mobility transistor grown on 1×1 cm2 larger patterns, the device exhibits maximum drain current density of 776 mA/mm and maximum transconductance of 101 mS/mm.