Al_0.75Ga_0.25N/Al_xGa_1-xN/Al_0.75Ga_0.25N/AlN/SiC Metal–Oxide–Semiconductor Heterostructure Field-Effect Transistors With Symmetrically-Graded Widegap Channel

Abstract

Novel Al 0.75 Ga 0.25 N/Al x Ga 1−x N/Al 0.75 Ga 0.25 N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with symmetrically-graded widegap Al x Ga 1−x N channel (x = 0.75 → 0.25 → 0.75) grown on a SiC substrate are investigated. Al 2 O 3 was devised as the gate dielectric by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. Device characteristics with respect to different etch depths of the source/drain recesses were studied. For a 2μm gate length (L G), the present widegap V-shape-channel MOS-HFET has shown improved maximum drain-source current density (I DS,max) of 299.3 A/mm at V DS = 20 V, I DS density at V GS = 0 V (I DSS0) of 153.9 mA/mm, on/off-current ratio (I on /I off) of 1.4 × 10 7 , extrinsic transconductance (g m,max) of 16.7 mS/mm, two-terminal off-state gate-drain breakdown voltage (BV GD) of −379 V, and three-terminal on-state drain-source breakdown voltage (BV DS) of 339 V. Besides, superior deep-UV sensing performance with high spectral responsivity (SR) of 1780 (810.2) A/W at wavelength λ = 250 (300) nm are also achieved. INDEX TERMS Al x Ga 1−x N, MOS-HFET, symmetrically-graded, widegap channel, Al 2 O 3 , non-vacuum ultrasonic spray pyrolysis deposition, spectral responsivity, deep-UV.

Improved Electrical and Deep-UV Sensing Characteristics of Al2O3-Dielectric AlGaN/AlN/SiC MOS-HFETs

“…Flow rates for the mixed etching gases of BCl 3 and Cl 2 were set at 10 sccm and 20 sccm, respectively. Optimum contact resistance characteristics can be obtained 31 by depositing the source/drain electrodes on the exposed channel surface. The 20 nm undoped Al 0.75 Ga 0.25 N barrier was, then, etched away before deposition of the Ti (10 nm)/Al (50 nm)/Ni (10 nm)/Au (50 nm) metal stack.…”

Investigations on Wide-Gap Al0.21Ga0.79N Channel MOS-HFETs With In0.12Al0.76Ga0.12N Barrier/Buffer and Drain Field-Plate

“…Similar polarization effects were maintained to provide appropriate comparison for the studied devices. Due to enhanced carrier confinement by the devised wide-gap In0.12Al0.76Ga0.12N or In0.12Al0.88N barrier/buffer, the obtained n2DEG values are higher than our previous works [15][16] and other InAlN/AlGaN device [25]. Moreover, the n and n-n2DEG product of sample B have been significantly enhanced due to the improved interfacial property in the In0.12Al0.76Ga0.12N/AlN/Al0.21Ga0.79N heterostructure.…”

“…Besides, the transfer length method (TLM) [28] was employed to measure the specific contact resistivity (ρc) and contact resistances (RC). ρc and RC were characterized to be 8.7 × 10 -6 (1.8 × 10 -5 ) Ω-cm 2 and 0.18 (0.26) Ω-mm for samples B1-B2 (A1), which are much lower than those wide-gap channel devices of our previous works [15][16]. It is mainly contributed by the devised n-GaN capping layer to greatly improve the source/drain ohmic contacts.…”

“…Consequently, enhanced gm, max performances have been achieved by the improved current densities in the present samples B1 and B2. The devised MOS-HFETs are superior to our previous woks [15][16] and other wide-gap-channel devices of gm, max = 16 mS/mm and IDS,max = 90 mA/mm [25], gm, max = 9 mS/mm and IDS, max = 350 mA/mm [29], IDS, max = 114 mA/mm [30], gm, max = 38 mS/mm and IDS, max = 635 mA/mm [31], IDS, max = 420 mA/mm [32], gm,max = 2.4 mS/mm and IDS, max = 13 mA/mm [33], and gm, max = 97.9 mS/mm and IDS, max = 473 mA/mm [34].…”

“…are needed. Our previous works have studied Si-doped AlGaN channel MOS-HFETs [15][16] showing depletion-mode operation and F --implanted AlGaN barrier MOS-HFET [17] exhibiting enhancement-mode characteristics. This work presents, for the first time, wide-gap Al0.21Ga0.79N channel MOS-HFETs with designs of In0.12Al0.76Ga0.12N barrier/buffer and drain field-plate (DFP).…”