For a while now, wide bandgap (WBG) materials, such as gallium nitride (GaN), have been well recognized for power devices owing to their high critical electric field and faster switching speeds. While significant research efforts have been performed on lateral GaN devices, lower power conversion efficiency and current drivability in lateral devices, compared to vertical devices, have diverted interest toward vertical power devices.11. H. Ohta, N. Kaneda, F. Horikiri, Y. Narita, T. Yoshida, T. Mishima, and T. Nakamura, “ Vertical GaN p-n junction diodes with high breakdown voltages over 4 kV,” IEEE Electr. Device Lett. 36, 1180–1182 (2015). https://doi.org/10.1109/LED.2015.2478907 More recently, the availability of high quality free standing GaN substrates have aided in faster advancements in vertical GaN power devices.22. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG09 Development of vertical devices has soon translated into unlocking GaN's full potential for high power applications. The Baliga figure of merit (BFOM) of these power devices is defined as VB2/Ron, where VB is the breakdown voltage and Ron is the specific on-resistance. Specifically, for GaN pn power diodes, to achieve a high VB, a thick drift layer with low doping concentration is required. So far, 5 kV breakdown voltage has been demonstrated on devices with a drift layer thickness of 33 μm with a step doping profile design22. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG09 and over 6 kV breakdown on devices with a drift layer thickness of 50 μm.33. A. L. Yates, B. P. Gunning, M. H. Crawford, J. Steinfeldt, M. L. Smith, V. M. Abate, J. R. Dickerson, A. Binder, A. A. Allerman, A. M. Armstrong, and R. J. Kaplar, “ Demonstration of 6.0-kV breakdown voltage in large area vertical GaN p-n diodes with step-etched junction termination extensions,” IEEE Trans. Electron Devices 69(4), 1931 (2022). https://doi.org/10.1109/TED.2022.3154665On the other hand, to achieve a low Ron, a thin drift layer with high electron mobility is required. Devices with an intrinsic Ron value of 0.15 mΩ cm2 after p-contact resistance deduction has been reported using a drift layer with a thickness of 12 μm.44. K. Nomoto, Z. Hu, B. Song, M. Zhu, M. Qi, N. Kaneda, and T. Mishima, “ 1.7 kV and 0.55 mΩ-cm2 GaN pn diodes on Bulk GaN Substrates with Avalanche Capability,” IEEE Electron Device Lett. 37(2), 161 (2016). https://doi.org/10.1109/LED.2015.2506638 Therefore, for a high BFOM, a diode structure with optimized low drift layer concentration, high electron mobility, low contact resistance, and efficient edge termination techniques would be required. Up to this date, a BFOM of 20, 16.5, and 7.18 GW/cm2 have been demonstrated using a 33, 12, and a 50 μm drift layer with a breakdown voltage of 5, 1.7, and 6.4 kV, respectively.2–42. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG093. A. L. Yates, B. P. Gunning, M. H. Crawford, J. Steinfeldt, M. L. Smith, V. M. Abate, J. R. Dickerson, A. Binder, A. A. Allerman, A. M. Armstrong, and R. J. Kaplar, “ Demonstration of 6.0-kV breakdown voltage in large area vertical GaN p-n diodes with step-etched junction termination extensions,” IEEE Trans. Electron Devices 69(4), 1931 (2022). https://doi.org/10.1109/TED.2022.31546654. K. Nomoto, Z. Hu, B. Song, M. Zhu, M. Qi, N. Kaneda, and T. Mishima, “ 1.7 kV and 0.55 mΩ-cm2 GaN pn diodes on Bulk GaN Substrates with Avalanche Capability,” IEEE Electron Device Lett. 37(2), 161 (2016). https://doi.org/10.1109/LED.2015.2506638 In this work, with a thinner drift layer, we demonstrate GaN pn diodes with a breakdown of above 4.9 kV and a BFOM of about 27 GW/cm2.Figure 1(a) shows a detailed schematic structure of the p–n diode. The layer structure contains a 2 μm thick n+ layer (2 × 1018 cm−3) followed by ∼28 μm n− drift layer (Nd–Na: 1 × 1015 cm−3) and a 500 nm p-GaN layer (Mg concentration: 1 × 1019 cm−3) capped with a thin p+-20 nm GaN layer (Mg concentration: 5 × 1019 cm−3). The GaN-on-GaN epi-structure was grown on a 352 μm thick 2 in. Gankiban™ near an equilibrium ammonothermal (NEAT) GaN substrate with an electron concentration of ≥8 × 1018 cm−3, an average dislocation density of  ∼1 × 105 cm−2, and a miscut angle of ∼0.2°.Prior to the metal organic chemical vapor deposition (MOCVD) epitaxy, the substrate was cleaned by diluted HCl and piranha solution. Trimethylgallium (TMGa) and ammonia (NH3) were used as the group-III and group-V precursors, respectively. The drift layer was intentionally doped with Si using the diluted silane as the n-type precursor. As the drift layer is significantly thicker than our previous 1 (Ref. 55. V. Talesara, Y. Zhang, Z. Chen, H. Zhao, and W. Lu, “ GaN power p–n diodes on hydride vapor epitaxy GaN substrates with near-unity ideality factor and <0.5 mΩ cm2 specific on-resistance,” Phys. Status Solidi RRL 16, 2100599 (2022). https://doi.org/10.1002/pssr.202100599) and 1.5 kV diodes,66. V. Talesara, Y. Zhang, Z. Chen, H. Zhao, and W. Lu, “ Design and development of 1.5 kV vertical GaN pn diodes on HVPE substrate,” J. Mater. Res. 36, 4919–4926 (2021). https://doi.org/10.1557/s43578-021-00435-8 a lower V/III ratio and a faster TMGa flow rate were used for a fast growth rate. The growth rate of the GaN drift layer is ∼5 μm/h with [C] measured to be 1–2 × 1016 cm−3 by secondary ion mass spectroscopy (SIMS). The detailed growth condition and impurity analysis can be found in Ref. 77. Y. Zhang, Z. Chen, W. Li, A. R. Arehart, S. A. Ringel, and H. Zhao, “ Metalorganic chemical vapor deposition gallium nitride with fast growth rate for vertical power device applications,” Phys. Status Solidi A 218, 2000469 (2021). https://doi.org/10.1002/pssa.202000469. This growth ran for about 5 h and 40 min which resulted in a 28 μm drift layer. Bis(cyclopentadienyl)-magnesium (Cp2Mg) was used as the p-type dopant in the p-GaN and p+-GaN layers. Hall measurements on p-GaN calibration samples grown under the same condition showed that the hole density is ∼1017 cm−3 with a mobility of 12 cm2/V s. The layer structure was designed based on analytical calculations to achieve 5 kV breakdown, considering a hypothetical 65% breakdown efficiency. Then, numerical simulations were performed for device structure design. Guard rings (GRs) and a spin-on-glass (SoG) layer for passivation were introduced in the simulations for electrical field management and mitigation. Ion implantation induced guard rings and isolation were chosen as the edge termination technique since it also helps in effective electric field management by providing a partially compensated pGaN layer.7,87. Y. Zhang, Z. Chen, W. Li, A. R. Arehart, S. A. Ringel, and H. Zhao, “ Metalorganic chemical vapor deposition gallium nitride with fast growth rate for vertical power device applications,” Phys. Status Solidi A 218, 2000469 (2021). https://doi.org/10.1002/pssa.2020004698. J. Wang, L. Cao, J. Xie, E. Beam, R. McCarthy, C. Youtsey, and P. Fay, “ High voltage, high current GaN-on-GaN p-n diodes with partially compensated edge termination,” Appl. Phys. Lett. 113, 023502 (2018). https://doi.org/10.1063/1.5035267 The GR optimization study performed for this structure follows the same process found in Ref. 55. V. Talesara, Y. Zhang, Z. Chen, H. Zhao, and W. Lu, “ GaN power p–n diodes on hydride vapor epitaxy GaN substrates with near-unity ideality factor and <0.5 mΩ cm2 specific on-resistance,” Phys. Status Solidi RRL 16, 2100599 (2022). https://doi.org/10.1002/pssr.202100599 for all three parameters: (i) number of GRs, (ii) GR width, and (iii) GR spacing.55. V. Talesara, Y. Zhang, Z. Chen, H. Zhao, and W. Lu, “ GaN power p–n diodes on hydride vapor epitaxy GaN substrates with near-unity ideality factor and <0.5 mΩ cm2 specific on-resistance,” Phys. Status Solidi RRL 16, 2100599 (2022). https://doi.org/10.1002/pssr.202100599 As seen in Figs. 1(b)–1(d), a design of 6 GRs with a width of 5 μm and spacing of 10 μm was used as the final device design. In this design, as shown in Figs. 1(e) and 1(f), the peak electric field in the GaN layer is close to 3.5 MV/cm at a bias of 6.4 kV.For device fabrication, Ni/Pt/Au and Ti/Al/Ni/Au metal stacks were used for p-contact and n-contact, respectively. The transmission line method (TLM) study was conducted to get optimized p-contacts on the sample. To get the lowest contact resistance, the p-contacts were annealed at 515 °C for 90 s in nitrogen ambient. Figures 2(a) and 2(b) display the I–V relationship of a TLM pattern and the plot of resistance as a function of spacings. The optimized p-contact resistance was measured to be 9.2 × 10−5 Ω cm2. Using the TLM study, n-contact resistance was measured to be 6.1 × 10−6 Ω cm2. The six GR designs were implemented by five nitrogen ion implantations at different energy and dose levels. The condition for each implant is as follows: (i) energy: 380 keV, dose: 3.2 × 1013 ions/cm2; (ii) energy: 230 keV, dose: 9.8 × 1012 ions/cm2; (iii) energy: 115 keV, dose: 6.7 × 1012 ions/cm2; (iv) energy: 45 keV, dose: 5 × 1012 ions/cm2; and (v) energy: 12.5 keV, dose: 1 × 1013 ions/cm2. A Photo-resist (PR) mask was used for these implants to create the GR and isolation. For the implanted region, ions are directly implanted on GaN. As shown in the simulated ion profile in Fig. 3, a fairly well box-type profile is formed. A 1.7 μm thick SiO2 covered SoG film was implemented for surface passivation. The devices have a circular active region of 500 μm in diameter.Measurements on this device were performed using Agilent 4156 and Agilent B1506A for forward and reverse leakage characteristics and a high-voltage power supply for breakdown measurements. These measurements were performed at room temperature while the sample was immersed in flourinert to reduce the risk of air breakdown. Before Spin-On-Glass (SOG) passivation, we performed capacitance–voltage (CV) measurement to confirm the drift layer doping concentration. Figure 4(a) shows the CV profile of the diode and Fig. 4(b) shows the drift layer doping concentration extracted using the CV data. The drift layer concentration (Nd+–Na−) of the device is close to 1 × 1015 cm−3.Though the CV data only show the Nd+–Na− profile at the top of the drift layer, it has been shown that the concentration is uniform if the same growth condition is used for the entire drift layer by SIMS.1,71. H. Ohta, N. Kaneda, F. Horikiri, Y. Narita, T. Yoshida, T. Mishima, and T. Nakamura, “ Vertical GaN p-n junction diodes with high breakdown voltages over 4 kV,” IEEE Electr. Device Lett. 36, 1180–1182 (2015). https://doi.org/10.1109/LED.2015.24789077. Y. Zhang, Z. Chen, W. Li, A. R. Arehart, S. A. Ringel, and H. Zhao, “ Metalorganic chemical vapor deposition gallium nitride with fast growth rate for vertical power device applications,” Phys. Status Solidi A 218, 2000469 (2021). https://doi.org/10.1002/pssa.202000469The forward I–V characteristics of the diode is shown in Fig. 5(a). The diode has a turn on voltage of 4.8 V at 100 A/cm2 and an on-state resistance (Ron) of 0.9 mΩ cm2, normalized with the device anode area. The relative high turn-on voltage is a result of a thin insulating layer formed at the beginning of the epitaxy process, due to the high background Fe impurity introduced from the coating material on the susceptor during the growth of the epilayers.9,109. Y. Zhang, Z. Chen, W. Li, H. Lee, M. R. Karim, A. R. Arehart, S. A. Ringel, S. Rajan, and H. Zhao, “ Probing unintentional Fe impurity incorporation in MOCVD homoepitaxy GaN: Toward GaN vertical power devices,” J. Appl. Phys. 127, 215707 (2020). https://doi.org/10.1063/5.000875810. T. Narita, M. Horita, K. Tomita, T. Kachi, and J. Suda, “ Why do electron traps at EC–0.6 eV have inverse correlation with carbon concentrations in n-type GaN layers?,” Jpn. J. Appl. Phys., Part 1 59, 105505 (2020). https://doi.org/10.35848/1347-4065/abb9ca The effects of this layer become more apparent when looking at the semi-log plot of the forward bias characteristics. This can be seen in the inset of Fig. 5(a). The thin insulating causes the additional blocking voltage which results in the higher turn-on voltage. This is also the reason for a relatively higher ideality factor of about 2.1. The device exhibited an extremely low Ron, which is attributed to the very low contact resistances and the high-quality epitaxial layers with precise and uniform doping control in the drift layer grown on the Gankiban™ GaN substrate with a low dislocation density. In addition, the increase in conductive holes from deep Mg acceptors also contributes on the conductivity at device turn-on, which is a result of an enhanced photon-recycling effect due to the high-quality epi-layers. The Mg acceptors are excited by the photons generated through electron–hole pair recombination at the p–n junction, an effect commonly seen in a direct-energy bandgap semiconductor, such as GaN.11–1511. K. Mochizuki, T. Mishima, K. Nomoto, A. Terano, and T. Nakamura, “ Optical-thermo-transition model of reduction in on-resistance of small GaN p–n diodes,” Jpn. J. Appl. Phys., Part 1 52(8), 08JN10 (2013). https://doi.org/10.7567/JJAP.52.08JN1012. K. Mochizuki, T. Mishima, Y. Ishida, Y. Hatakeyama, K. Nomoto, N. Kaneda, T. Tshuchiya, A. Terano, T. Tsuchiya, H. Uchiyama, S. Tanaka, and T. Nakamura, “ Determination of lateral extension of extrinsic photon recycling in p-GaN by using transmission-line-model patterns formed with GaN p–n junction epitaxial layers,” Jpn. J. Appl. Phys., Part 1 52, 08JN22 (2013). https://doi.org/10.7567/JJAP.52.08JN2213. K. Mochizuki, K. Nomoto, Y. Hatakeyama, H. Katayose, T. Mishima, N. Kaneda, T. Tsuchiya, A. Terano, and T. Ishigaki, “ Photon-recycling GaN p-n diodes demonstrating temperature-independent, extremely low on-resistance,” in International Electron Devices Meeting ( IEEE, 2011), pp. 26.3.1–26.3.4.14. K. Mochizuki, “ Vertical GaN bipolar devices: Gaining competitive advantage from photon recycling,” Phys. Status Solidi A 214(3), 1600489 (2017). https://doi.org/10.1002/pssa.20160048915. Z. Hu, K. Nomoto, B. Song, M. Zhu, M. Qi, M. Pan, X. Gao, V. Protasenko, D. Jena, and H. G. Xing, “ Near unity ideality factor and Shockley-Read-Hall lifetime in GaN-on-GaN p-n diodes with avalanche breakdown,” Appl. Phys. Lett. 107, 243501 (2015). https://doi.org/10.1063/1.4937436 Figure 5(b) shows the breakdown characteristics of the device. This measurement was done using a high voltage power supply and a current recording LabVIEW program. The power supply can measure up to 10 kV with a current resolution of 1 μA. The device shows avalanche breakdown at 4926 V at a current density of 2 mA/cm2. Compared with the numerical simulation result, a breakdown efficiency of 77% is achieved. The high VB value represents one of the highest reported breakdown voltages for a vertical GaN p–n diode. This is remarkable as the device has a thinner drift layer than what has been reported with a similar or lower breakdown voltage.1–31. H. Ohta, N. Kaneda, F. Horikiri, Y. Narita, T. Yoshida, T. Mishima, and T. Nakamura, “ Vertical GaN p-n junction diodes with high breakdown voltages over 4 kV,” IEEE Electr. Device Lett. 36, 1180–1182 (2015). https://doi.org/10.1109/LED.2015.24789072. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG093. A. L. Yates, B. P. Gunning, M. H. Crawford, J. Steinfeldt, M. L. Smith, V. M. Abate, J. R. Dickerson, A. Binder, A. A. Allerman, A. M. Armstrong, and R. J. Kaplar, “ Demonstration of 6.0-kV breakdown voltage in large area vertical GaN p-n diodes with step-etched junction termination extensions,” IEEE Trans. Electron Devices 69(4), 1931 (2022). https://doi.org/10.1109/TED.2022.3154665 It is also worthy to mention that our layer design has a uniformly low doped (Nd–Na: 1 × 1015 cm−3) drift layer instead of thicker step doping profile as reported in other devices with high breakdown voltages.2,32. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG093. A. L. Yates, B. P. Gunning, M. H. Crawford, J. Steinfeldt, M. L. Smith, V. M. Abate, J. R. Dickerson, A. Binder, A. A. Allerman, A. M. Armstrong, and R. J. Kaplar, “ Demonstration of 6.0-kV breakdown voltage in large area vertical GaN p-n diodes with step-etched junction termination extensions,” IEEE Trans. Electron Devices 69(4), 1931 (2022). https://doi.org/10.1109/TED.2022.3154665 The low doping concentration in the drift layer is critical for a high VB, yet a low Ron is still achieved due to the high electron mobility. Figures 5(c) and 5(d) show the reverse leakage up to 200 V and 3 kV, respectively. Due to the equipment current resolution and voltage bias limits, the reverse leakage current was measured using two pieces of equipment at different bias ranges. As shown in Fig. 5(c), the reverse leakage at −200 V is 1 × 10−7 A/cm2. This is measured using Agilent 4156 which has a higher current resolution and lower noise levels, therefore showing the true leakage current at 200 V. The leakage current of the same device measured up to 3 kV using Agilent B1506A is 1.5 × 10−5 A/cm2. The noise floor level for B1506A is higher, resulting in higher leakage current at lower bias range.Figure 6 shows a comparison of Ron vs VB of a recently reported state of the art pn GaN power diodes with VB > 2 kV (Refs. 1–41. H. Ohta, N. Kaneda, F. Horikiri, Y. Narita, T. Yoshida, T. Mishima, and T. Nakamura, “ Vertical GaN p-n junction diodes with high breakdown voltages over 4 kV,” IEEE Electr. Device Lett. 36, 1180–1182 (2015). https://doi.org/10.1109/LED.2015.24789072. H. Ohta, K. Hayashi, F. Horikiri, M. Yoshino, T. Nakamura, and T. Mishima, “ 5.0 kV breakdown-voltage vertical GaN p–n junction diodes,” Jpn. J. Appl. Phys., Part 1 57, 04FG09 (2018). https://doi.org/10.7567/JJAP.57.04FG093. A. L. Yates, B. P. Gunning, M. H. Crawford, J. Steinfeldt, M. L. Smith, V. M. Abate, J. R. Dickerson, A. Binder, A. A. Allerman, A. M. Armstrong, and R. J. Kaplar, “ Demonstration of 6.0-kV breakdown voltage in large area vertical GaN p-n diodes with step-etched junction termination extensions,” IEEE Trans. Electron Devices 69(4), 1931 (2022). https://doi.org/10.1109/TED.2022.31546654. K. Nomoto, Z. Hu, B. Song, M. Zhu, M. Qi, N. Kaneda, and T. Mishima, “ 1.7 kV and 0.55 mΩ-cm2 GaN pn diodes on Bulk GaN Substrates with Avalanche Capability,” IEEE Electron Device Lett. 37(2), 161 (2016). https://doi.org/10.1109/LED.2015.2506638, 66. V. Talesara, Y. Zhang, Z. Chen, H. Zhao, and W. Lu, “ Design and development of 1.5 kV vertical GaN pn diodes on HVPE substrate,” J. Mater. Res. 36, 4919–4926 (2021). https://doi.org/10.1557/s43578-021-00435-8, and 16–2316. Y. Hatakeyama, K. Nomoto, N. Kaneda, T. Kawano, T. Mishima, and T. Nakamura, “ Over 3.0 GW/cm2 figure-of-merit GaN p-n junction diodes on free-standing GaN substrates,” IEEE Electron Device Lett. 32, 1674–1676 (2011). https://doi.org/10.1109/LED.2011.216712517. A. M. Armstrong, A. A. Allerman, A. J. Fischer, M. P. King, M. S. Van Heukelom, M. W. Moseley, R. J. Kaplar, J. J. Wierer, M. H. Crawford, and J. R. Dickerson, “ High voltage and high current density vertical GaN power diodes,” Electron. Lett. 52, 1170–1171 (2016). https://doi.org/10.1049/el.2016.115618. I. C. Kizilyalli, A. P. Edwards, O. Aktas, T. Prunty, and D. Bour, IEEE Trans. Electron Devices 62, 414–422 (2015). https://doi.org/10.1109/TED.2014.236086119. I. C. Kizilyalli, T. Prunty, and O. Aktas, “ 4-kV and 2.8-mΩ-cm2 vertical GaN p-n diodes with low leakage currents,” IEEE Electron Device Lett. 36, 1073–1075 (2015). https://doi.org/10.1109/LED.2015.247481720. K. Nomoto, Z. Hu, B. Song, M. Zhu, M. Qi, R. Yan, V. Protasenko et al., “ GaN-on-GaN p-n power diodes with 3.48 kV and 0.95 mΩ-cm2: A record high figure-of-merit of 12.8 GW/cm2,” in IEEE International Electron Devices Meeting (IEDM) ( IEEE, 2015), pp. 9.7.1–9.7.4.21. I. C. Kizilyalli, A. P. Edwards, H. Nie, D. Disney, and D. Bour, “ High voltage vertical GaN p-n diodes with avalanche capability,” IEEE Trans. Electron Devices 60, 3067–3070 (2013). https://doi.org/10.1109/TED.2013.226666422. S.-W. H. Chen, H.-Y. Wang, C. Hu, Y. Chen, H. Wang, J. Wang, W. He, X. Sun, H.-C. Chiu, H.-C. Kuo, W. Wang, K. Xu, D. Li, and X. Liu, “ Vertical GaN-on-GaN PIN diodes fabricated on free-standing GaN wafer using an ammonothermal method,” J. Alloys Compd. 804, 435–440 (2019). https://doi.org/10.1016/j.jallcom.2019.07.02123. Y. Hatakeyama, K. Nomoto, A. Terano, N. Kaneda, T. Tsuchiya, T. Mishima, and T. Nakamura, “ High-breakdown-voltage and low-specific-on-resistance GaN p–n junction diodes on free-standing GaN substrates fabricated through low-damage field-plate process,” Jpn. J. Appl. Phys., Part 1 52, 028007 (2013). https://doi.org/10.7567/JJAP.52.028007) with the device from this work, in together with theoretical Si, SiC, and GaN limits. With the VB value of 4926 V and the Ron value of 0.9 mΩ cm2, the device has a BFOM of 27 GW/cm2. This is one of the highest BFOM ever reported on GaN power devices. The low Ron value is attributed to the low contact resistances and the high mobility of the drift layer. As the p-GaN and n-GaN contact resistances are orders lower than the measured Ron value, the on-resistance is dominated by the drift layer resistance. Considering the electron concentration at 1015 cm−3, this suggests an electron mobility of 1380 cm2/V s in the drift layer. Overall, the superior device performance is attributed to the optimized device structure design, high quality substrate, and epitaxial growth and fabrication processes. Further improvement in breakdown voltage can be expected by the addition of field plates and refining the passivation layer to mitigate the electrical field and avoid breakdown at the edge of the electrodes.

In summary, we have demonstrated GaN-on-GaN pn power diodes with a breakdown voltage of 4.9 kV and BFOM of 27 GW/cm2 using a relative thin 28 μm drift layer with a doping concentration of 1 × 1015 cm−3 and high-quality epitaxial layers. The high device performance is the result of a combination of low dislocation density GaN bulk substrate, high quality epi-layers, low p-contact resistance, and effective edge termination techniques implemented in the device structure.

The authors would like to thank Edward Letts and Tadao Hashimoto from the Six Point Materials for providing the Gankiban™ bulk GaN substrate and Dr. Anant K. Agarwal from the Ohio State University for assistance with breakdown measurements.

Conflict of Interest

The authors have no conflicts to disclose.

Author Contributions

Vishank Talesara: Data curation (lead); Formal analysis (lead); Investigation (lead); Writing – original draft (lead); Writing – review & editing (equal). Yuxuan Zhang: Data curation (equal); Methodology (equal). Vijay Gopal Thirupakuzi Vangipuram: Data curation (equal); Methodology (equal). Hongping Zhao: Conceptualization (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal). Wu Lu: Conceptualization (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.

REFERENCES

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