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The role of defects on Schottky and Ohmic contact characteristics for GaN and AlGaN/GaN high-electron mobility transistors

Walker, Dennis Eugene, Jr.
http://rave.ohiolink.edu/etdc/view?acc_num=osu1141766860

Abstract Details

2006, Doctor of Philosophy, Ohio State University, Electrical Engineering.
The AlGaN/GaN material system is ideally suited for UV detectors, light sources, and high performance, high power transistors. Through an understanding of the physics and device properties associated with defects, engineered solutions can allow the utilization of the full potential of AlGaN/GaN device properties. Auger Electron Spectroscopy (AES) and secondary electron threshold (SET) techniques allow the characterization of band bending and work function at semiconductor surfaces. Using these techniques with ultra-high vacuum (UHV) sample cleaving and metal deposition, Schottky barrier formation to non-polar GaN was investigated revealing cases of both ideal band-bending and Fermi level pinning. Cathodoluminescence spectroscopy (CL) allows the investigation of luminescent defect levels with depth-resolving capability by controlling the incident beam voltage and associated electron beam penetration into the sample. High electron mobility transistors (HEMTs) exhibiting current collapse were investigated using CL and CL mapping and specific defects were found in the GaN channel and buffer regions that may help explain the current collapse phenomena. Coupling a novel gate mask into a typical HEMT fabrication sequence and utilizing three, independent UHV sample cleaning techniques including thermal desorption of contaminants, Ga-reflux, and N2 ion sputtering, and metallization of the gates on AlGaN/GaN HEMTs, correlations in defect levels, surface cleaning technique, and finished device performance were found. In analyzing the CL data for this sample, however, a specific feature located just below the GaN near band edge was observed to accumulate near the Ohmic contacts prompting a further investigation of both the effects of the RIE etch used in producing the UHV-compatible mask as well as four different Ohmic contact structures on both defect levels determined by CL and on final device performance. Finally, a bulk GaN sample was processed with Ohmic contacts to determine the correlation of the AlGaN device layer in the formation of this defect level associated with the Ohmic contacts and the role of the mesa RIE etch on the same defect. Through these investigations, progress in the underlying physics of Schottky barrier formation on GaN and the important role of defects on device performance using AES, SET, and CL have been demonstrated.
Leonard Brillson (Advisor)
239 p.
GaN; AlGaN; HEMT; Schottky; Ohmic; contacts; CL; cathodoluminescence; UHV; surface cleaning; Auger; AES; RIE; defect; current collapse; cleave

Recommended Citations

Citations

  • Walker, Jr., D. E. (2006). The role of defects on Schottky and Ohmic contact characteristics for GaN and AlGaN/GaN high-electron mobility transistors [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1141766860

    APA Style (7th edition)

  • Walker, Jr., Dennis. The role of defects on Schottky and Ohmic contact characteristics for GaN and AlGaN/GaN high-electron mobility transistors. 2006. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1141766860.

    MLA Style (8th edition)

  • Walker, Jr., Dennis. "The role of defects on Schottky and Ohmic contact characteristics for GaN and AlGaN/GaN high-electron mobility transistors." Doctoral dissertation, Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1141766860

    Chicago Manual of Style (17th edition)

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© 2006, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.