Self‐aligned normally‐off metal–oxide–semiconductor n⁺⁺GaN/InAlN/GaN high electron mobility transistors

Abstract

Self-aligned normally-off n þþ GaN/InAlN/AlN/GaN MOS HEMTs with a recessed gate show scalable threshold voltage between 1.3 to 3.7 V, which increases with the gate oxide thickness. Al 2 O 3 or HfO 2 gate insulators were grown by ALD at 100 8C so that one photoresist mask could be used for the gate recessing, ALD and metal lift-off. A low density of the barrier surface donors $1 Â 10 13 cm À2 stems from the low thermal budged during the HEMT processing and explains the threshold voltage behaviour. Maximal I DS reaches $0.4 A/mm despite 2-mm gate length and 8-mm source-to-gate distance invariant to the threshold voltage. It is shown that for the present device Al 2 O 3 provides better gate insulation than HfO 2 , however, the latter may be more appropriate for highly scaled short gate-length HEMTs.Schematic picture of the self-aligned InAlN/GaN MOS HEMT.

Creation of Two‐Dimensional Electron Gas and Role of Surface Donors in III‐N Metal‐Oxide‐Semiconductor High‐Electron Mobility Transistors

“…It was reported by several groups that ionized surface donors residing at the III‐N MOS interface can fully compensate the semiconductor surface polarization charge P S , while the density of surface donors ( N d,surf ) can be modified by tailored surface treatment . Particularly we reported that AlGaN/GaN surface pretreatment by HCl prior Al 2 O 3 metal‐organic chemical vapor deposition (MOCVD) followed by post‐deposition annealing (PDA) can lead to fully compensating N d,surf ≈− P S / q , where q is the elementary charge .…”

Low-temperature atomic layer deposition-grown Al2O3 gate dielectric for GaN/AlGaN/GaN MOS HEMTs: Impact of deposition conditions on interface state density

“…[7][8][9] In this case, normally-off device operation can be achieved, and, moreover, V th can be increased by oxide thickness (t ox ) increasing to a desired value. 8,10,11 However, polarization charge at the barrier surface is fully compensated in most of the cases by the charge referred here to as surface donors, while its origin and nature has not been understood yet.…”

“…Recently, Al 2 O 3 and HfO 2 grown by ALD at 100 C provided normally-off operation of InAlN/GaN MOS-HEMT with positive V th shift compared to the reference Schottkygated structure and V th increase with the increase in t ox . 11 This has been attributed to the reduction of the surface donors' density from 4.5 to about 1 Â 10 13 cm À2 as a result of low deposition temperature (T D ) during ALD. 11 It has been proposed by several authors that surface donors are located at or close to oxide/III-N barrier interface.…”

“…11 This has been attributed to the reduction of the surface donors' density from 4.5 to about 1 Â 10 13 cm À2 as a result of low deposition temperature (T D ) during ALD. 11 It has been proposed by several authors that surface donors are located at or close to oxide/III-N barrier interface. [7][8][9] Therefore, a possible relationship between N DS and distribution of the oxide/barrier interface traps (D it ) represents a relevant question, yet not explored in more detail in the a) Electronic mail: milan.tapajna@savba.sk literature.…”

Threshold voltage controlled by gate area and gate recess in inverted trapezoidal trigate AlGaN/GaN MOS high-electron-mobility transistors with photoenhanced chemical and plasma-enhanced atomic layer deposition oxides

“…2(c) indicate that our device offers a low gate leakage current density of 3 × 10 −8 A=mm at the gate voltage sweep from −3 to +3 V, which is comparable to that of the state-of-the-art Emode planar Al 2 O 3 =GaN ++ =InAlN=AlN=GaN MOS-HEMT but with superior SS performance to the latter. 24 and 2(c) yield a device threshold of V th = 1.2 V, a peak transconductance g m of 38 mS=mm, a field-effect mobility μ FE of ∼250 cm 2 V −1 s −1 , and a drain-induced barrier lowering (DIBL) factor of 110 mV=V. The ON-resistance of the devices is 6 Ω mm, and the estimated breakdown voltage is no less than 20 V. The device I DS and g m values are not higher than those reported previously, 25) owing to (i) the originally lower sheet carrier density at the planar AlGaN=GaN HEMT heterointerface and (ii) the processing-related gate recess depth that intrudes into the AlGaN barrier thickness, which leads to further reduction in the level of 2DEG associated with our inverted-trapezoid fin-FET channel.…”