Neutron Radiation Effects in Epitaxially Laterally Overgrown GaN Films

Abstract

Neutron radiation effects were studied in undoped n-GaN films grown by epitaxial lateral overgrowth (ELOG). The irradiation leads to carrier removal and introduces deep electron traps with activation energy 0.8 eV and 1 eV. After the application of doses exceeding 10 17 cm -2 , the material becomes semiinsulating n-type, with the Fermi level pinned near the level of the deeper electron trap. These features are similar to those previously observed for neutron irradiated undoped n-GaN prepared by standard metal-organic chemical vapor deposition (MOCVD). However, the average carrier removal rate and the deep center introduction rate in ELOG samples is about five-times lower than in MOCVD samples. Studies of electron beam induced current (EBIC) show that the changes in the concentration of charged centers are a minimum in the low-dislocation-density laterally overgrown regions and radiation-induced damage propagates inside these laterally overgrown areas from their boundary with the high-dislocation-density GaN in the windows of the ELOG mask.

Neutron irradiation on AlGaN/GaN high electron mobility transistors on SiC substrates

“…Activation energy of electron traps created by neutron bombardment is in the range of 0.21-1.0 eV which is dependent on neutron irradiation dose (10 À 14 -10 À 17 cm À 2 ) and epitaxial structure [14][15][16]. Trapped electrons can be excited back to the conduction band with optical activation at room temperature.…”

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

“…Neutron irradiation greatly increases the concentration of these centers [220]. From measurements of the electric field dependence of the trap energy they are believed to be donors [17,220].…”

“…The traps concentration was found to increase upon irradiation with heavy particles (neutrons, He ions) (see e.g. [17,220,223]). For heavily neutron irradiated n-and p-GaN the Fermi level was pinned close to the position of these traps.…”

“…It was noticed that, for insufficient injection levels in ODLTS, the apparent activation energy of the HT1 traps could be considerably higher than the actual ionization energy that can be consistently measured only at injection levels providing the traps saturation [84]. The density of the HT1 traps was noticed to increase at initial stages of electron and neutron irradiation [203,220,233]. The thermal activation energy of the HT1 trap determined from ODLTS measurements coincided very reasonably with the optical ionization energy of the deep acceptor responsible for the yellow luminescence band near 2.15 eV, as determined from detailed PL spectra versus temperature and versus excitation level measurements [14].…”

Radiation Damage in GaN‐Based Materials and Devices

“…Neutron irradiation of undoped ELOG GaN fi lms resulted in a much lower effective removal rate than for standard MOCVD material, 1 cm -1 versus 5 cm -1 [61]. The Fermi level position in heavily irradiated material is also the same suggesting that no strong changes in the structure of the core regions of DRs occur with changing the dislocation density.…”