- Title
- Investigation of AlGaN films and nickel/AlGaN Schottky diodes using depth-dependent cathodoluminescence spectroscopy and secondary ion mass spectrometry
- Author
- Bradley, Shawn Todd
- Degree
- Doctor of Philosophy, Ohio State University,
Electrical Engineering, 2004.
- Advisor
- Leonard J Brillson
- Pages
- xxii, 182 p.
- Abstract
- AlGaN/GaN heterostructures and high Al mole fraction AlGaN films are used in a wide variety of applications, such as high power/high frequency transistors, UV photodetectors, solar-blind detectors, light-emitting diodes, and laser diodes. However, there are several important issues that need to be addressed in AlGaN/GaN heterostructures, such as the impact of defect states on electronic properties such as mobility and two-dimensional electron gas (2DEG) sheet charge density as well as the role of surface processing on the Schottky barrier height. Also, Si doping of AlGaN with high Al mole fraction has been shown to be difficult and may be restricted by non-intentional impurities and their associated deep levels (such as O), as well as an increasing dopant donor energy with higher Al mole fraction. Correlations have been made between deep level defects and the 2DEG sheet charge density, interface broadening, surface roughness, and Ga-N ratios. Depth-dependent cathodoluminescence spectroscopy (CLS) and secondary ion mass spectrometry (SIMS) reveal the nature of deep level defects and their effect on Si doping of high Al mole fraction (25%-100%) AlGaN. SIMS results provide correlations between AlGaN deep level emissions from CLS and elemental impurities, such as oxygen, distributed through the epitaxial bulk films. Cross-sectional CLS measurements of the AlGaN/sapphire interface reveal luminescence signatures which correlate with oxygen diffusing from the sapphire into the AlGaN. Internal photoemission spectroscopy (IPE) reveals changes in the Schottky barrier height of Ni on AlGaN/GaN heterojunction field effect transistor structures (HFETs) with pre-metallization processing conditions and post-metallization ultra-high vacuum annealing. These variations in the IPE Schottky barrier height are correlated with AlGaN near band edge emissions from low energy electron-excited nanoluminescence spectroscopy (LEEN) and Ni/AlGaN interface impurities by SIMS. It is shown that changes in the Schottky barrier height and the appearance of dual barriers are dominated by changes in the local Al mole fraction. CL mapping reveals spatial variations in the AlGaN near band edge emission which could lead to the appearance of dual Schottky barriers.
- Keywords
- GaN; AlN; AlGaN; gallium nitride; nitride; LEEN; cathodoluminescence; CL; IPE; internal photoemission spectroscopy; secondary ion mass spectrometry; SIMS; Schottky; doping; HFET; HEMT; UHV
Document number: osu1078329692.
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