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Development of MOCVD GaN Homoepitaxy for Vertical Power Electronic Device Applications

Zhang, Yuxuan
http://orcid.org/0000-0002-5052-4342
http://rave.ohiolink.edu/etdc/view?acc_num=osu1658407231414771

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Gallium nitride (GaN) represents a wide bandgap semiconductor material that has been widely utilized in optoelectronic and electronic devices. As silicon (Si) based power devices are quickly approaching their fundamental material limits, GaN exhibits great potential for next generation power electronic devices due to its wide bandgap (3.4 eV), high breakdown field (3.3 MV/cm), and high electron mobility (1500 cm2/(V∙s)). With the availability of free-standing GaN substrates, GaN vertical power devices with superior performances have been demonstrated. One of the key challenges to further advance the GaN vertical power devices lies in the development of high quality, thick GaN epitaxy with low background doping and high mobility. This dissertation focuses on the development of high-quality GaN metal-organic chemical vapor deposition (MOCVD) growths and vertical GaN PN diodes for high performance power electronic applications. The sources and incorporation mechanisms of typical compensations in GaN MOCVD are investigated. The pre-growth wafer cleaning process and growth susceptor are identified as two major sources of iron (Fe) impurity incorporation. The (EC-0.6) eV defect peak is confirmed to be associated with Fe impurity. Fe impurity can be suppressed with proper wafer cleaning and full coverage of susceptor pocket. An optimized MOCVD GaN growth condition with a typical growth rate (GR) of 2 µm/hr is established as the baseline with low controllable doping (Nd-Na) at 4×1015 cm-3. Background carbon (C) impurity typically increases monotonically with GR. The high background C impurity in MOCVD GaN is related to the low pyrolysis efficiency of NH3. Laser-assisted MOCVD (LA-MOCVD) growth technique is proposed to address this issue using a 9.219 µm wavelength carbon dioxide (CO2) laser. The LA-MOCVD shows higher effective V/III ratios via efficient NH3 decomposition. The background [C] in LA-MOCVD GaN films decreases monotonically as the laser power increases. A low [C] at 5.5×1015 cm-3 was achieved with the GaN GR of 4 µm/hr and high electron mobility of 1200 cm2/(V∙s) via the LA-MOCVD technique. With optimized process gas flow distributions and introduction of LA-MOCVD, relatively low [C] at 2.1×1016 cm-3 is achieved with a fast GR of 8.6 µm/hr. A theoretical thermodynamic model is proposed to investigate the correlations between [C] and GR, which reveals that [C] increases faster with GR at the faster GR regime. LA-MOCVD is demonstrated as an effective method to reduce the C incorporation, particularly under fast growth rate conditions. Furthermore, the use of GaN substrate with optimal off-cut angle can be a potential method to further reduce [C]. High performance vertical GaN PN diodes are developed. Devices grown on halide vapor phase epitaxy (HVPE) substrates show high breakdown voltage with uniform low ideality factor and on resistance (Ron). By optimizing growth condition and device design, a breakdown voltage (VBR) of 4.9 kV and low Ron of 0.9 mΩ.cm2 are achieved. The device demonstrated a record Baliga’s Figure of merit of 27 GW/cm2. The non-destructive wafer scale optical characterization methods based on cathodoluminescence (CL) and photoluminescence (PL) are utilized to probe the free-standing GaN substrates, epi-layer and correlate the optical features with device performance. This potentially can serve as an effective approach to predict wafer scale device yield.
Hongping Zhao (Advisor)
Wu Lu (Committee Member)
Anant Agarwal (Committee Member)
Aaron Arehart (Committee Member)
157 p.
Electrical Engineering; Materials Science
gallium nitride; vertical power devices; metalorganic chemical vapor deposition; laser-assisted MOCVD; carbon impurity; iron impurity; fast growth rate; defects; thermodynamic modelling; optical characteristics

Recommended Citations

Citations

  • Zhang, Y. (2022). Development of MOCVD GaN Homoepitaxy for Vertical Power Electronic Device Applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658407231414771

    APA Style (7th edition)

  • Zhang, Yuxuan. Development of MOCVD GaN Homoepitaxy for Vertical Power Electronic Device Applications. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1658407231414771.

    MLA Style (8th edition)

  • Zhang, Yuxuan. "Development of MOCVD GaN Homoepitaxy for Vertical Power Electronic Device Applications." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658407231414771

    Chicago Manual of Style (17th edition)

osu1658407231414771
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This open access ETD is published by The Ohio State University and OhioLINK.