Demonstration of Quasi-AlGaN/GaN HFET Using Ultrathin GaN/AlN Superlattices as a Barrier Layer

We demonstrate a quasi-AlGaN/GaN heterostructure field-effect transistor (HFET). A quasi-AlGaN barrier layer consists of ultrathin GaN/AlN superlattices (SLs), resulting in low sheet resistance in the heterostructures. The dc characteristics show a large maximum drain current density (I
_dmax
= 830 mA/mm) and low on-resistance (R
_on
= 4.3 Ω·mm) with a source-drain separation of 12 μm. The I
_d
reduction is less than 3% after the dc bias stress test, indicating that the current collapse is greatly suppressed in our device even without a passivation film deposited on the channel surface. GaN/AlN SLs are considered to obstruct the transmission of carriers toward surface traps, thus the suppression of the current collapse. The quasi-AlGaN/GaN HFET will be useful for high-frequency high-power high-speed switching applications with low energy loss.