Enhancement of AlGaN/GaN high electron mobility transistors off-state drain breakdown voltage via backside proton irradiation

Abstract

Proton irradiation from the backside of the samples were employed to enhance off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for subsequent backside proton irradiation. By taking the advantage of the steep drop at the end of proton energy loss profile, the defects created by the proton irradiation from the backside of the sample could be precisely placed at specific locations inside the AlGaN/GaN HEMT structure. There were no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for the irradiated AlGaN/GaN HEMTs with the proton energy of 225 or 275 keV, for which the defects created by the proton irradiations were intentionally placed in the GaN buffer. HEMTs with defects placed in the two dimensional electron gas (2DEG) channel region and AlGaN barrier using 330 or 340 keV protons not only showed degradation of both drain current and extrinsic transconductance but also exhibited improvement of the off-state drain breakdown voltage. The Florida Object Oriented Device and Process Simulator Technology Computer Aided Design finite-element simulations were performed to confirm the hypothesis of a virtual gate formed around the 2DEG region to reduce the peak electric field around the gate edges and increase the off-state drain breakdown voltage.

Review—Ionizing Radiation Damage Effects on GaN Devices

“…176 Proton damage.-Displacement damage has a strong dependence on particle energy particularly for protons. [176][177][178][179][180][181][182][183][184][185][186] For energies below 30 MeV, protons interact with the nucleus through Rutherford scattering. Low-energy protons, which travel more slowly, transfer more energy than protons with higher energy due to their reduced velocity, increasing the cross section.…”

Simulation of Radiation Effects in AlGaN/GaN HEMTs

“…Li et al showed that no performance change to the devices occurred for irradiation cases where the defects did not reach the AlGaN/GaN interface. 17 We also note that the acceptor traps will be fully ionized near the 2DEG for a wide range of trap energies; thus the resultant outcome is insensitive to the acceptor trap energy. Other defects such as N interstitials or Ga-N divancancies 9 may also be prominent; however it is the donor traps that are the limiting factor.…”

“…In general, protonbased radiation damage to AlGaN/GaN HEMTs results in mobility degradation and an increase in the threshold voltage, both of which lead to reductions in peak transconductance and drain current. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The change in mobility has the potential to be greater in magnitude than changes observed in the other parameters. For example Lu et al measured 40% reduction in mobility and only a 0.1V shift (3% change) in threshold voltage and 13% reduction in drain saturation current for a specific case of proton radiation.…”

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

“…On one hand, the collisions cause electrons generation and recombination in the heterostructure, producing vacancies and defects in the device. These vacancies and defects would lead to sheet carrier density and carrier mobility decrease, and result in a positive shift in VTH and a decrease in current density [26,29,33]. On the other hand, during the collision of protons and electrons, heat would be generated in the heterostructure, which would be partial cause of the diffusion between the metals [5].…”