Ultralow nonalloyed Ohmic contact resistance to self aligned N-polar GaN high electron mobility transistors by In(Ga)N regrowth

Abstract

Ultralow Ohmic contact resistance and a self-aligned device structure are necessary to reduce the effect of parasitic elements and obtain higher ft and fmax in high electron mobility transistors (HEMTs). N-polar (0001¯) GaN HEMTs, offer a natural advantage over Ga-polar HEMTs, in terms of contact resistance since the contact is not made through a high band gap material [Al(Ga)N]. In this work, we extend the advantage by making use of polarization induced three-dimensional electron-gas through regrowth of graded InGaN and thin InN cap in the contact regions by plasma (molecular beam epitaxy), to obtain an ultralow Ohmic contact resistance of 27 Ω μm to a GaN 2DEG.

A Comparison of N-Polar () GaN Surface Preparations for the Atomic Layer Deposition of Al2O3

“…5 Nitrogen-polar GaN has potential advantages over Ga-polar GaN for high-frequency applications due to its low contact resistance and a natural back barrier to improve electron confinement. [6][7][8] For example, an extremely low contact resistance of 23 -μm was reported by Mishra et al 9 To date, most of the N-polar GaN HEMT devices employ structures with a Schottky barrier as the gate contact. 6,10,11 However, a metaloxide-semiconductor structure is preferred, as it provides a higher input impedance, larger gate voltage swings, and lower gate leakage currents.…”

“…[6][7][8] For example, an extremely low contact resistance of 23 -μm was reported by Mishra et al 9 To date, most of the N-polar GaN HEMT devices employ structures with a Schottky barrier as the gate contact. 6,10,11 However, a metaloxide-semiconductor structure is preferred, as it provides a higher input impedance, larger gate voltage swings, and lower gate leakage currents. 12,13 Aluminum oxide (Al 2 O 3 ) is an excellent gate dielectric for IIInitride based devices due to its large bandgap (7∼9 eV), relatively high dielectric constant (∼9) and high thermal stability (up to 1000…”

“…6,10,11 However, a metaloxide-semiconductor structure is preferred, as it provides a higher input impedance, larger gate voltage swings, and lower gate leakage currents. 12,13 Aluminum oxide (Al 2 O 3 ) is an excellent gate dielectric for IIInitride based devices due to its large bandgap (7∼9 eV), relatively high dielectric constant (∼9) and high thermal stability (up to 1000…”

Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

“…The intrinsic current unity gain cutoff frequency (fT,intrinsic) is directly proportional to the electron velocity in the channel. While parasitics do play an important role in the frequency performance, recent advances in ohmic contact technology have achieved ultra-low resistance 2,5,6 (< 0.1 Ω.mm), thereby making the channel transit delay the main component of the overall delay in GaN HEMTs. Monte Carlo simulations in GaN have predicted peak electron drift velocities as high as 3 x 10 7 cm/s, with comparatively lower saturation velocities up to ~ 2 x 10 7 cm/s, limited mainly by optical phonon scattering [7][8][9][10][11] .…”

Ohmic contact formation between metal and AlGaN/GaN heterostructure via graphene insertion

“…In addition, the hightemperature annealing steps preclude the use of some advanced fabrication approaches, such as gate-first, self-aligned processing. While regrown contacts 22,23 and implantation 24 provide an alternative, these approaches also add to the complexity of the processing.…”