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Semi-insulating Gallium nitride was irradiated by fast and thermal neutrons with fluences from 1014to 1016 n/cm2. Depth-resolved cathodoluminescence spectroscopy was used to determine defects changes before and after irradiation. The results revealed two kinds of defects affected near-band emission recombination from two opposite directions. One was attributed to irradiation-induced N vacancies that contribute to near-band emission recombination. Another was attributed to irradiation-induced deep level defects that contribute to sub-band gap recombination and thus decrease the near-band emission recombination. [ABSTRACT FROM AUTHOR]

We use depth-resolved cathodoluminescence spectroscopy (DRCLS), Kelvin probe force microscopy (KPFM), and surface photovoltage spectroscopy (SPS) on a nanometer scale to map the temperature, strain, and defects inside GaN high-electron-mobility transistors. DRCLS maps temperature at localized depths, particularly within the 2-D electron gas region during device operation. KPFM maps surface electric potential across the device, revealing lower potential patches that decrease rapidly with increasing off-state stress. CL spectra acquired at these patches exhibit defect emissions that increase with both on- and off-state stresses and that increase with decreasing surface potential. SPS also reveals features of deep level gap states generated after device operation that reduce near-band-edge emission and increase surface band bending. Our nanoscale measurements are consistent with defect generation by inverse piezoelectric field-induced stress at the gate edge on the drain side at high voltage. [ABSTRACT FROM PUBLISHER]

The authors have used ultrahigh vacuum surface science techniques combined with gate mask fabrication and processing to demonstrate improvements in the unity gain cutoff frequency response fT of AlGaN/GaN high electron mobility transistors compared to standard processing. In situ annealing, nitrogen ion sputtering and annealing, and Ga reflux plus annealing all displayed increased fT response on average. In situ depth-resolved cathodoluminescence spectroscopy of the AlGaN/GaN interface region reveals changes in GaN near-band edge, 2.2 eV, and 2.9 eV native defect emissions consistent with the average device performance between process steps and between devices with the same treatment on the same wafer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]