Breakdown Enhancement of AlGaN/GaN HEMTs on 4-in Silicon by Improving the GaN Quality on Thick Buffer Layers

We have achieved a 9- $\mu\hbox{m}$-thick AlGaN/GaN high-electron mobility transistor (HEMT) epilayer on silicon using thick buffer layers with reduced dislocation density $(D_{D})$. The crack-free 9- $\mu\hbox{m}$-thick epilayer included 2- $\mu\hbox{m}$ i-GaN and 7- $ \mu\hbox{m}$ buffer. The HEMTs fabricated on these devices showed a maximum drain–current density of 625 mA/mm, transconductance of 190 mS/mm, and a high three-terminal OFF breakdown of 403 V for device dimensions of $L_{g}/W_{g}/L_{\rm gd} = \hbox{1.5/15/3} \ \mu\hbox{m}$ . Without using a gate field plate, this is the highest $BV$ reported on an AlGaN/GaN HEMT on silicon for a short $L_{\rm gd}$ of 3 $\mu\hbox{m}$. A very high $BV$ of 1813 V across 10- $\mu \hbox{m}$ ohmic gap was achieved for i-GaN grown on thick buffers. As the thickness of buffer layers increased, the decreased $D_{D}$ of GaN and increased resistance between surface electrode and substrate yielded a high breakdown.