Ion-Implanted GaN/AlGaN/GaN HEMTs with Extremely Low Gate Leakage Current
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Ion-Implanted GaN/AlGaN/GaN HEMTs with Extremely Low Gate Leakage Current Kazuki Nomoto1, Taku Tajima1, Tomoyoshi Mishima2, Masataka Satoh1, and Tohru Nakamura1 1 EECE, HOSEI University, 3-11-15 Midori-cho, Koganei, 184-0003, Japan 2 R&D Group, Hitachi Cable Ltd., Tsuchiura, 300-0026, Japan ABSTRACT We were demonstrated the realization of compatibility of extremely low gate leakage current and low source resistance with Si ion-implanted (I/I) GaN/AlGaN/GaN surface-stabilized high-electron mobility transistor (HEMT) without any recess etching process. The source/drain (S/D) regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into source/drain regions with energy of 80 keV, the performances were significantly improved. On-resistance (Ron) reduced from 105 to 9.2 Ω·mm. Saturation drain current (Idss) and maximum transconductance (gmMAX) increased from 49 to 527 mA/mm and from 13 to 84 mS/mm (Vg=+1V). INTRODUCTION The AlGaN/GaN high-electron mobility transistors (HEMTs) have been studied as a candidate for high power devices for the RF amplifiers and power electronics systems [1]. One of the most important features of this material system is its large piezo-electric polarization in the strained AlGaN, which generates highly dense two-dimensional electron gas (2DEG) with concentrations of exceeding 1013 /cm2. High-power RF device performances have been demonstrated [2], [3], however, there is a large room to be improved considering the excellent material properties. Such a discrepancy has been caused mainly by a high parasitic resistance including high ohmic contact resistances. Thus, reduction of the parasitic resistance, dominated by so-called source resistance in AlGaN/GaN HEMTs is crucial for further improvement in their RF performance. Moreover, there is gate leakage current and current collapse as a further problem of the device. With the conventional GaN-based HEMTs, a practical solution to this issue is to use a recess-gate structure [4], [5] in which a heavily doped cap layer with a narrow bandgap should be precisely etched off with little damage at the gate region. Ion implantation is one of the most indispensable technologies for impurity doping especially in silicon based integrated circuits. However, few reports are published about application of ion implantation to the active regions [6], [7] except for isolation in GaN devices [8], [9], because Si ions have to be implanted at a high temperature above room temperature to get effective dopant activation, and crystal damage recovery of implanted GaN requires higher temperature annealing above 1500 oC with a N2 overpressure over 100-bar than the GaN epitaxial temperature. In this paper, in order to overcome the abovementioned issue, we demonstrate novel I/I GaN/AlGaN/GaN HEMTs. The thin surface undoped GaN was effective in stabilizing surface states resulting in reduction of the current collapse with maintaining the low gate leakage current without any precise etching process [10].
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