Effect of electron irradiation on AlGaN/GaN and InAlN/GaN heterojunctions

Abstract

AlGaN/AlN/GaN/sapphire, AlGaN/GaN/sapphire, AlGaN/GaN/Si, and InAlN/GaN/sapphire heterojunctions (HJs) were irradiated with 10 MeV electrons to fluences of 2 × 1015 to 3.3 × 1016 cm−2. The main effects on the electrical properties were a decrease in two-dimensional electron gas (2DEG) mobility and the shift of capacitance–voltage (C-V) characteristics to more positive values. The 50% 2DEG mobility decrease occurred at a similar fluence of 3.3 × 1016 cm−2 for all AlGaN/GaN and AlGaN/AlN/GaN HJs, but at a much lower fluence of 1.3 × 1016 cm−2 for InAlN/GaN, which is in line with previous observations for neutron irradiated HJs. The shift of C-V characteristics is due to increased concentration of deep acceptor traps in the barrier/interface region. In AlGaN/GaN/Si transistors, the increase of concentration of deep barrier/interface traps with activation energy of 0.3, 0.55, and 0.8 eV was observed. This increase correlates with the observed degradation of gate lag characteristics of transistors after irradiation with 1.3 × 1016 cm−2 electrons.

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…We detected centers with similar behavior in MOCVD grown InAlN heterojunctions [268]. They were also found to increase in concentration after neutron [268] or electron [269] irradiation. These data suggest the participation of major technologically important contaminants (most likely, O, C) forming complexes with native defects created by irradiation.…”

“…The reason for that is the undercutting the 2DEG portion of the channel below the Schottky diode and thus increasing the effects of series resistance. In that sense multifinger rectangular Schottky diodes with narrow fingers are preferable (see [265,267,269,270]). …”

Review—Ionizing Radiation Damage Effects on GaN Devices

“…The rate of electron irradiation induced parameter changes of the AlN/GaN HEMTs was found to be about an order of magnitude slower than that of AlGaN/GaN HEMTs. 91 This was explained by the much thinner barrier in the AlN case and, hence, the lower energy impacted into lattice defects formation by irradiating electrons in such a barrier. The main effect of electron irradiation of AlGaN/AlN/GaN, AlGaN/GaN, and InAlN/GaN heterojunctions (HJs) grown by MOCVD on sapphire and of AlGaN/GaN heterojunctions grown by MOCVD on Si (111) is the decrease of 2DEG mobility of heterojunctions with consequent increase of the sheet resistivity, while the 2DEG concentration was effected only slightly.…”

“…The main effect of electron irradiation of AlGaN/AlN/GaN, AlGaN/GaN, and InAlN/GaN heterojunctions (HJs) grown by MOCVD on sapphire and of AlGaN/GaN heterojunctions grown by MOCVD on Si (111) is the decrease of 2DEG mobility of heterojunctions with consequent increase of the sheet resistivity, while the 2DEG concentration was effected only slightly. 91 The decrease in threshold voltage of AlGaN/GaN/Si HJs and HEMTs can be explained by an increase of the density of deep acceptor traps. DLTS and admittance measurements on AlGaN/GaN/Si HEMTs and admittance spectra measurements on AlGaN/GaN/Si HJs show that the traps involved have activation energies of 0.3, 0.45, 0.55, and 0.8 eV.…”

“…From DLTS and admittance spectra results it seems reasonable to associate this decrease with the increased density of barrier/interface traps with activation energy 0.3, 0.45, 0.55, and 0.8 eV introduced by irradiation. 91 Coming back to the point that radiation exposure increases the concentration of defects already present in the GaN, Figure 16 shows a schematic representation of energy levels in the gap of both n-and p-type GaN before and after proton irradiation. 71,78 Note how many of the defects already present in the material increase after proton irradiation.…”