GaN–AlGaN heterostructure field-effect transistors over bulk GaN substrates

We report on AlGaN/GaN heterostructures and heterostructure field-effect transistors (HFETs) fabricated on high-pressure-grown bulk GaN substrates. The $\text{2d}$ electron gas channel exhibits excellent electronic properties with room-temperature electron Hall mobility as high as $\text{μ=1650\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V s}$ combined with a very large electron sheet density $n_s{\text{≈1.4×10}}^{13} {\mathrm{cm}}^{\mathrm{-2}}.$ The HFET devices demonstrated better linearity of transconductance and low gate leakage, especially at elevated temperatures. We also present the comparative study of high-current AlGaN/GaN HFETs ${\mathrm{(n}}_s{\text{μ>2×10}}^{16} {\mathrm{V}}^{\mathrm{-1}}{\mathrm{ s}}^{\mathrm{-1}}\mathrm{)}$ grown on bulk GaN, sapphire, and SiC substrates under the same conditions. We demonstrate that in the high-power regime, the self-heating effects, and not a dislocation density, is the dominant factor determining the device behavior.