The effects of proton irradiation on the electrical properties of NbAlO/AlGaN/GaN MIS-HEMT

Abstract

AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors (MIS-HEMTs) with atomic layer deposited (ALD) NbAlO gate dielectric were investigated using 3 MeV proton irradiation at a fluence of 10 15 p/cm 2 . It was found that the proton irradiation damage caused degradation in DC performance and a flatband voltage shift in the capacitance-voltage curve. Gate-drain conductance measurements indicated that new traps were introduced in GaN from the irradiation, and the trap densities increased from 1.18×10 12 cm 2 eV 1 to 1.82×10 12 cm 2 eV 1 in MIS-HEMTs after irradiation. However, these increases in trap densities caused by irradiation in MIS-HEMT are less than those in HEMT, which can be attributed to the protection of the AlGaN surface by the NbAlO dielectric layer. AlGaN/GaN, MIS-HEMT, proton irradiation, trap PACS number(s): 85.30.Tv, 73.40.Qv, 77.55.+f, 61.82.Fk Citation:AlGaN/GaN high electron-mobility transistors (HEMTs) have recently emerged as attractive transistors suitable for high-power and high-frequency applications [1]. However, larger gate leakage currents in HEMTs due to surface defects and the finite barrier height of AlGaN limit the performance and reliability of devices, especially the breakdown voltage and power handling capabilities [2]. Previously, several groups have attempted to solve this problem by applying the metal-insulator-semiconductor (MIS) structure. For example, S i O 2 [3], Al 2 O 3 [4], and HfO 2 [5] have all been widely used for gate dielectric layers. The high-k dielectric layer can be thickened without reducing the transconductance of HEMTs. In this paper, we choose atomic layer deposition (ALD) Nb0.1Al0.9O as the gate insulator layer, because it has a larger bandgap (6.7) than HfO 2 and a higher dielectric constant (15) than Al 2 O 3 . The NbAlO MISHEMTs have been fabricated successfully and the gate leakage current decreased about three orders of magnitude less than HEMT [6]. In addition, GaN-based devices are radiation harder than GaAs devices, and hence are known for several unique applications, such as satellite-based communication systems and nuclear industry applications [7], in which devices would be set in place where they are exposed to a great deal of particle radiation. Therefore, GaN-based devices are expected to have higher resistance against radiation than conventional devices. Previous studies observed significant degradation in the performances of AlGaN/GaN HEMTs after a fluence of 10 14 10 15 p/cm 2 1.8 MeV protons [8]. The degradation is identified by a decrease in the maximum transconductance, an increase in the threshold voltage, and a decrease in the drain saturation

Effects of Gd2O3 Gate Dielectric on Proton-Irradiated AlGaN/GaN HEMTs

“…During transconductance measurements, the Schottky gate HEMTs showed a 29% decrease of the peak transconductance (gm,max), and the MOS-HEMTs showed only a 10% reduction. Positive shift in the VTH was observed in the conventional and MOS-HEMT, in good agreement to those in the Schottky-and MOS-diodes, with a similar tendency as MIS-HEMTs using NbAlO after irradiation [14].…”

“…Studies of irradiation effects on AlGaN/GaN based HEMTs and MOS-HEMTs (using Al2O3 [13], NbAlO [14], SiO2 [15], MgO or Sc2O3 [16]) have been explored using different energies and fluences, experimentally [6,7] and by simulation [21]- [23]. For instance, the Al2O3/AlGaN/GaN MOS-HEMTs showed over 50% decrease in maximum drain current after 5×10 15 cm -2 fluence irradiation with 5 MeV protons [13].…”

“…For instance, the Al2O3/AlGaN/GaN MOS-HEMTs showed over 50% decrease in maximum drain current after 5×10 15 cm -2 fluence irradiation with 5 MeV protons [13]. NbAlO AlGaN/GaN Metal Insulator Semiconductor (MIS) HEMTs with Si3N4 passivation showed a decrease in DC-IV properties after 3 MeV proton irradiation with 1×10 15 cm -2 fluence [14]. However, the degradation mechanisms of the devices after irradiation are still unclear in many cases.…”