AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors using Sc2O3 as the gate oxide and surface passivation

We demonstrated that ${\mathrm{Sc}}_2{\mathrm{O}}_3$ thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, $I_{\mathrm{DS}},$ reaches a value of over 0.8 A/mm and is $\text{∼40\%}$ higher on ${\mathrm{Sc}}_2{\mathrm{O}}_3/\mathrm{AlGaN}/\mathrm{GaN}$ transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that ${\mathrm{Sc}}_2{\mathrm{O}}_3$ retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to $\text{+6\hspace{0.17em}}\mathrm{V}$ of gate voltage. In particular, ${\mathrm{Sc}}_2{\mathrm{O}}_3$ is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.