AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with 4 nm thick Al₂O₃ gate oxide

Abstract

AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with 4 nm thick Al 2 O 3 gate oxide were prepared and their performance was compared with that of AlGaN/GaN HFETs. The MOSHFETs yielded ∼40% increase of the saturation drain current compared with the HFETs, which is larger than expected due to the gate oxide passivation. Despite a larger gate-channel separation in the MOSHFETs, a higher extrinsic transconductance than that of the HFETs was measured. The drift mobility of the MOSHFETs, evaluated on large-gate FET structures, was significantly higher than that of the HFETs. The zero-bias mobility for MOSHFETs and HFETs was 1950 cm 2 V -1 s -1 and 1630 cm 2 V -1 s -1 , respectively. These features indicate an increase of the drift velocity and/or a decrease of the parasitic series resistance in the MOSHFETs. The current collapse, evaluated from pulsed I−V measurements, was highly suppressed in the MOSHFETs with 4 nm thick Al 2 O 3 gate oxide. This result, together with the suppressed frequency dispersion of the capacitance, indicates that the density of traps in the Al 2 O 3 /AlGaN/GaN MOSHFETs was significantly reduced.

Characterization of interface states in Al2O3/AlGaN/GaN structures for improved performance of high-electron-mobility transistors

“…GaN-based MOS-HEMTs using an Al 2 O 3 as the insulator have been demonstrated by many groups. 3,4,[6][7][8][9] The typical values of bandgap and permittivity reported for the Al 2 O 3 film are 7-9 eV and 8-10, respectively. [6][7][8][9][10] The Al 2 O 3 film prepared by atomic layer deposition (ALD), in particular, showed relatively low electronic state densities in the Al 2 O 3 /n-GaN system.…”

“…3,4,[6][7][8][9] The typical values of bandgap and permittivity reported for the Al 2 O 3 film are 7-9 eV and 8-10, respectively. [6][7][8][9][10] The Al 2 O 3 film prepared by atomic layer deposition (ALD), in particular, showed relatively low electronic state densities in the Al 2 O 3 /n-GaN system. 9,[11][12][13] However, in the MOS-HEMT structures, the insulator/semiconductor interface is usually formed on the AlGaN/GaN heterostructures, resulting in the existence of two interfaces under the gate electrode.…”

Temperature-Dependent Interface-State Response in an Al2O3/n-GaN Structure

“…Al 2 O 3 has often been applied to the insulated-gate AlGaN/GaN HEMTs [2,[9][10][11], although the properties of Al 2 O 3 /GaN or Al 2 O 3 /AlGaN interfaces are not yet well understood.…”

Device Performances Related to Gate Leakage Current in Al2O3/AlGaN/GaN MISHFETs

“…The use of thin gate insulator is also required to achieve the high frequency operation (ƒ T , ƒ max ) for RF devices [7][8][9]. The Al 2 O 3 layer, usually deposited by atomic layer deposition (ALD), has been widely used as a gate dielectric layer among other insulators because it offers high gate capacitance due to relatively high dielectric constant (9.1 eV), high breakdown field (10 MV·cm −1 ), and large conduction band offset of 2.1 eV with AlGaN layer which ensures low gate leakage current [10][11][12][13].…”