Effect of various interlayers on epiwafer bowing in AlGaN/GaN high-electron-mobility transistor structures

We have systematically studied the effect of various interlayers on epiwafer bowing in AlGaN/GaN high-electron-mobility transistor (HEMT) structures on sapphire substrates by using an interlayer insertion method. The interlayers including aluminum increase the epiwafer bowing independently of growth temperature. However, both InGaN-based interlayers and low-temperature-deposited GaN interlayers suppress the epiwafer bowing. When multilayers are used as interlayers, the effect on epiwafer bowing is enhanced compared with that in the case of using single interlayers. The minimum bowing values were lower than 10 μm, which were accomplished by using multilayers. The crystalline qualities of AlGaN/GaN HEMTs with interlayers were satisfactory and the performance of these HEMTs was better than that of conventional AlGaN/GaN HEMTs without interlayers. Epiwafers with reduced bowing exhibited a reduced strain in GaN layers compared with that of GaN layers with larger bowing, which indicates that strain control in the epitaxial layers is important for reducing the epiwafer bowing.