Neutron irradiation effects on gallium nitride-based Schottky diodes

Abstract

Depth-resolved cathodoluminescence spectroscopy (DRCLS), time-resolved surface photovoltage spectroscopy, X-ray photoemission spectroscopy (XPS), and current-voltage measurements together show that fast versus thermal neutrons differ strongly in their electronic and morphological effects on metal-GaN Schottky diodes. Fast and thermal neutrons introduce GaN displacement damage and native point defects, while thermal neutrons also drive metallurgical reactions at metal/GaN interfaces. Defect densities exhibit a threshold neutron fluence below which thermal neutrons preferentially heal versus create new native point defects. Scanning XPS and DRCLS reveal strong fluence-and metal-dependent electronic and chemical changes near the free surface and metal interfaces that impact diode properties. V

Impact of Mg content on native point defects in MgxZn1−xO (0 ≤ x ≤ 0.56)

“…Trap state densities measured by t-SPS correlate with DRCLS intensities and display relatively good agreement 40 with Gür et al DLOS results, 30 as expected from previous DLOS/t-SPS comparisons. 41,42 Total DLOS deep level concentrations for x = 0%, 31%, 44%, 52%, and 56% of 50.6, 6.1, 6.8, 7.8, and 5.4 × 10 16 cm −3 , respectively, 30 also correlate with Figure 4(a). The bulk I(V C )/I(NBE) values for ZnO are consistent with positron annihilation spectroscopy (PAS) calibration values corresponding to ∼0.08 × 10 17 cm −3 in the bulk and 0.25 × 10 17 cm −3 at the surface.…”

Review of using gallium nitride for ionizing radiation detection

“…The existence of the threshold neutron fluence on the performance of GaN Schottky diodes was further validated by Lin,124 which found that fast neutrons with fluences !10 15 n/cm 2 increases deep level defects densities, while thermal neutron with fluences 10 15 n/cm 2 anneal these defects and improve the GaN crystalline quality. Their further studies 125 revealed that both fast and thermal neutrons introduce recombination centers in GaN, forming an insulating phase between GaN and metal contact, raising the Schottky contact ideality factor, increasing the Ohmic contact sheet resistance, and lowering the current transport for both contacts.…”

Neutron irradiation effects on metal-gallium nitride contacts

“…The A* variation with fast neutron irradiation fluence can be explained by the decrease of the surface defect density according to the t-SPS measurement results. 20 However, surface defect variations do not account for the deviation of A* from the theoretical value for devices under fast þ thermal neutron irradiation. An A* anomaly caused by metal/GaN interfacial chemical reaction has been reported by other researchers [31][32][33] which is sometimes accompanied with barrier height reduction.…”

“…[17][18][19] Recently, we described the effect of fast (1 MeV) and thermal (25 meV) neutron irradiation on GaN Schottky diodes. 20 That work focused on the defect densities and depth distributions produced by fast and thermal neutrons in epitaxial n-GaN after irradiation. Using a combination of depth resolved cathodoluminescence spectroscopy (DRCLS), surface photovoltage spectroscopy (SPS), transient (t-) SPS, and current-voltage (I-V) measurements, we showed that fast neutron fluences !10 15 n/cm 2 increased densities of deep level defects, specifically the well-known yellow band (YB) and blue band (BB) defects.…”

“…Nevertheless, fast plus thermal neutron fluences !10 15 n/cm 2 increased these defects and a) degraded I-V characteristics at the Schottky and ohmic contacts of the irradiated diodes. 20 In order to understand this electrical degradation, it is important to separate the effects of neutrons on the GaN per se versus on the metal-GaN interface. To this end, we have used DRCLS, t-SPS, and I-V measurements to characterize how neutrons interact with GaN Schottky and ohmic contacts electrically and metallurgically for two metals, titanium, and nickel, after fast and thermal neutron irradiation.…”