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(Color online) XPS showing the Ga 3p spectra of two AlGaN/GaN samples coated with a thin HfAlO (∼1 nm) film. (a) Ga-O peaks are observed for the sample without VA and SiH4 treatment, and (b) Ga-O peak disappears for the sample with VA and SiH4 treatment, and a Si-O peak is detected. (c) Cross sectional TEM image of a TaN/HfAlO/AlGaN/GaN stack without in situ VA and SiH4 treatment, showing that a native oxide interfacial layer was formed on the AlGaN surface. (d) Cross sectional TEM image of a TaN/HfAlO/AlGaN/GaN stack with in situ VA and SiH4 treatment showing that an oxidized Si layer (∼1 nm) was formed on the AlGaN surface.
(Color online) (a) Measured Capacitance-Voltage (C-V) characteristics of the AlGaN/GaN MOS-HEMTs with and without in situ VA and SiH4 treatment. (b) Transfer (ID -VG ) characteristics, gate leakage current (IG -VG ), and transconductance (gm -VG ) of AlGaN/GaN MOSHEMTs with and without in situ VA and SiH4 treatment at VD = 5 V.
(Color online) Output (ID -VD ) characteristics of AlGaN/GaN MOS-HEMTs (a) without and (b) with in situ VA and SiH4 treatment, where VG is varied in steps of 1 V from −5 V to 4 V. A 53% enhancement of saturation drain current is observed for the device with in situ VA and SiH4 treatment over the control device at (VG - Vth ) of 7 V and VD of 15 V. From the fabricated devices, sheet resistance for device with passivation and control is 410 Ω/□ and 810 Ω/□, respectively. The specific contact resistivity for both devices is around 1.5 × 10−3 Ω cm2.
(a) Plot of Ion /Ioff ratio as a function of gate leakage current IG for AlGaN/GaN MOS-HEMTs without and with in situ VA and SiH4 treatment. The insert shows the gate leakage current density JG as a function of gate voltage VG for both devices. JG for device with passivation is suppressed by ∼3 orders at VG = 4 V. (b) Plot of subthreshold swing S [given by dVG /d(log10 ID )] as a function gate leakage current IG for AlGaN/GaN MOS-HEMTs without and with in situ VA and SiH4 treatment. A reduced interface state density is expected to give a smaller S and to reduce gate leakage current contributed by trap-assisted tunneling.
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