Demonstration of 1200 V/1.4 mΩ cm² vertical GaN planar MOSFET fabricated by an all ion implantation process

Abstract

We present a vertical GaN planar metal-oxide-semiconductor field-effect transistor (MOSFET) fabricated by an all ion implantation process. The fabricated MOSFET shows an on-resistance of 2.78 mΩ cm 2 and a breakdown voltage of 1200 V, by applying the short cell pitch design to reduce the on-resistance and a Mg and N sequential implantation to improve the breakdown voltage of the pn-junction. By evaluating each on-resistance component in the fabricated vertical GaN planar MOSFET using the simultaneously formed test structures, an effective on-resistance of the active region excluding the source parasitic resistance is 1.4 mΩ cm 2 . Consequently, it was demonstrated that an all ion implantation process can fabricate a vertical GaN planar MOSFET with a high breakdown voltage and low on-resistance. This result will greatly contribute to the realization of GaN power devices.

Lattice Location Studies of the Amphoteric Nature of Implanted Mg in GaN

“…We interpret this as the n-type character of the sample being changed by implantation towards intrinsic conditions. c) When the fluence of implanted Mg is increased above several 10 13 cm −2 by means of implanting the stable isotopes 24 Mg, 25 Mg or 26 Mg, the interstitial fractions of 27 Mg found in subsequent implantations of this radioisotope are significantly and progressively reduced to a few per cent only (Figure 4 and S4). This happens irrespective of the initial doping type of the sample, which at such high implanted fluences quite likely has been converted to intrinsic conditions.…”

“…We would like to point out that by means of stable 26 Mg implantations the amount of implanted Mg in the peak of the implantation profile reached values that exceeded several times the doping level of 2×10 19 cm −3 of Mg incorporated during growth of the GaN:Mg samples. We also note that the background-corrected sum fractions fi+fS of interstitial and substitutional 27 Mg stayed rather constant around 100% up to the highest implantation fluences used in the experiments, cf.…”

“…Independent of doping type, the amount of interstitial 27 Mgi found in samples implanted close to RT or 300°C with the stable isotopes 24 Mg, 25 Mg or 26 Mg at fluences above 10 14 cm −2 (the technologically relevant fluence range) is at maximum at the level of several per cent. In particular this means that the amount of stable Mg introduced during previous implantations or from doping during growth (2×10 19 cm −3 ) does not lead to a significant increase of the interstitial fraction for implanted 27 Mg or to Mg clustering at the fluences investigated here.…”

“…Implanting the radioactive ion beam of 27 Mg with sub-pA currents (fluence rates 0.5-6.3×10 8 cm −2 s −1 ) allowed to reach a maximum implantation fluence regime around 4-5×10 12 cm −2 , corresponding to 2.5-3.1×10 7 events on a single beam spot. In order to explore the fluence regime around 10 14 cm −2 , which is relevant for technological applications, we used the fact that ISOLDE is also able to deliver beams of the stable isotopes 24 Mg, 25 Mg and 26 Mg at considerably higher currents than 27 Mg. While the stable implantations were performed under the same conditions as using the radioactive ion beam, the currents ranged from 36 pA to 168 pA, corresponding to 0.6-2.9×10 10 cm −2 s −1 .…”

“…Recently, a number of novel approaches using Mg ion implantation and annealing have achieved very promising results regarding p-type doping, e.g. multicycle rapid thermal annealing (RTA), [19] high-temperature implantation around 500°C [19][20][21] or 1000°C, [22] ultra-high-pressure annealing, [8,[23][24] microwave annealing, [21] pulsed laser annealing, [25] or co-implantation of N. [26] However, also conventional RTA [20,27,28] or furnace annealing [29,30] has been reported successful and suitable for creating devices such as visible-blind photodiodes [29] or power rectifiers. [30] A crucial step for the electrical activation of the group II element Mg is its incorporation on substitutional Ga sites, since only in this lattice position it can act as an acceptor.…”