Abstract: A low sheet resistance of 95.5 Ω/□ at room temperature has been demonstrated in an MBE-grown Sc_0.15Al_0.85N/AlN/GaN epitaxial HEMT structure. Owing to the strong spontaneous and piezoelectric polarization of ScAlN, a large two-dimensional electron gas density of 7.8 × 10¹³ cm⁻² and a relatively high mobility of 836 cm²/V·s were demonstrated with a 15 nm Sc_0.15Al_0.85N barrier. Further investigation under low temperature on this structure reveals a reduced sheet resistance to 33.3 Ω/□ and mobility increased to 4223 cm²/V·s at 10 K. The dependence of sheet carrier density, mobility, and the associated sheet resistance on ScAlN thickness was further studied. The compelling electron transport properties demonstrated in the structure position ScAlN as a strong contender as the barrier layer in future GaN HEMT devices.

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