Spectroscopic and Electrical Characterization of SiO_x and GaN Device Structures as a Function of Irradiation

Detecting irradiation and protecting complementary-metal-oxide-semiconductor (CMOS) devices from harsh radiation environments is vital for electronics in space and national security. For CMOS devices, ionizing photons have enough energy to break bonds within SiO₂ causing electrons, holes, and radiolytic protons to be released. Holes will be trapped in E-prime centers and non-bridging oxygen hole centers (NBOHC), whereas radiatiolytic protons will form more positively charged P_b centers at the SiO₂/Si interface. To combat positive charge build-up after ionizing irradiation, plasma enhanced chemical vapor deposited (PECVD) SiO_x (x < 2) has been developed. PECVD SiO_x contains evenly distributed nanocrystalline (nc)-Si grains or a-Si nanoclusters that trap electrons and inhibit radiolytic proton movement. We took flatband voltage shift (V_FB) measurements after ionizing irradiation and found that V_FB is less in PECVD SiO_x than in SiO₂ because of the overall reduction in positive charge build-up. For as-deposited and annealed PECVD SiO_x, spatially resolved depth resolved cathodoluminescence spectroscopy (DRCLS) and spectroscopic elipsometry confirmed a strong electron trap related to a-Si nanoclusters at 3.87 eV and nc-Si grains at 3.92 eV below the conduction band of SiO₂, respectively. DRCLS after ionizing irradiation indicated that nc-Si grains are more efficient at trapping electrons. Finally, we observed that different plasma conditions for Si-rich SiO_x produced an observed shift in the DRCLS electron trap energy, which may account for hysteresis degradation. Furthermore, understanding how neutron irradiation affects GaN material and diodes, especially at high fluences, is important for future implementation of in neutron sensor applications. Hence, GaN Schottky diodes were irradiated with thermal neutrons (25 meV) and fast neutrons (1 MeV) at three different fluences (10¹⁴, 10¹⁵ and 10¹⁶ n/cm²) and we measured resulting defects optically and electrically. Below 1015 n/cm2, neutron irradiation decreased the density of defects that give blue band (BB) and yellow band (YB) emissions in GaN, a sign that neutrons annealed and recrystallized GaN. At neutron fluences = 10¹⁵ n/cm² the electrical properties of diodes degraded indicating 10¹⁴ n/cm² is the threshold fluence before significant damage starts to occur. After = 10¹⁵ fast neutron irradiation, the BB and YB GaN defects along with a radiation induced Ev + 1.4 eV trap state all increased near the surface. An increase in all three defects points to fast neutrons inducing regions of disorder in GaN. Moreover, fast + thermal neutrons exhibited the lowest forward I-V current and the highest sheet resistance, contact resistance, and ideality factor. However, the common GaN defects and Ev + 1.4 eV densities were lower than in the fast-only neutron case. These results suggested that thermal neutrons affected the metal contacts more than the GaN. Optical images, x-ray photoemission spectroscopy (XPS) and DRCLS showed that thermal neutrons induced oxygen and gallium rich localized melted regions that were insulating in nickel/GaN contacts. Thermal neutrons also caused nitrogen and gallium to incorporate into titanium, leaving semiconductor voids at the Ti/GaN interface.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Electrical and Computer Engineering

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Katz, Evan Jarrod

Contributors dc:contributor

• Brillson, Leonard

• Electrical Engineering

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1365770655

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1365770655