High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼1015 cm−3) 28  μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB) of 4.9 kV and a low specific on-resistance (RON) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2B/RON) of 27 GW/cm2.

A novel type-II InGaN-ZnSnGa2N4 quantum well (QW) structure is proposed based on recent experimental achievements for the successful epitaxy of ZnSnN2-GaN alloys and the determination of their band offsets with GaN. The simulation results indicate that this structure is promising as the active region for high-efficiency InGaN-based amber (λ ∼ 590 nm) light-emitting diodes (LEDs). The hole wavefunction in the valence band is better confined with the insertion of a monolayer scale of ZnSnGa2N4 into the InGaN QW while the electron wavefunction in the conduction band is better confined with the incorporation of an AlGaN layer in the GaN quantum barrier. The band structure of the InGaN-ZnSnGa2N4 QW is numerically simulated based on the experimentally measured band offsets between ZnSnGa2N4 and GaN. With the InGaN-ZnSnGa2N4 QW design, a low In content (20%) is required in the InGaN layer to reach a peak emission wavelength of ∼590 nm, yet an In composition of 25% is needed to reach the same emission wavelength for a conventional InGaN QW with the same layer thicknesses. Moreover, the electron-hole wavefunction overlap (Гe1−hh1) for the InGaN-ZnSnGa2N4 QW design reaches 18% for an emission wavelength at ∼590 nm. This result is much improved over the conventional InGaN QW overlap of 5% emitting at the same wavelength. The increase in electron-hole wavefunction overlap results in an approximately 14 times enhancement in the predicted spontaneous emission radiative recombination rate of the InGaN-ZnSnGa2N4 QW as compared to that of the conventional InGaN QW. This InGaN-ZnSnGa2N4 QW structure design can be promising to pave a new way to achieve high efficiency amber LEDs.

Pulsed-mode metal–organic chemical vapor deposition (MOCVD) growth of ZnSn­(Ga)­N2 on GaN-on-sapphire templates was investigated with the goal of developing stoichiometric, high-quality, epitaxial ZnSnN2-GaN films for integration with GaN-based device structures. It was determined that pulsed-mode growth, during which the Sn precursor was pulsed, enabled the achievement of higher growth temperatures and the avoidance of the formation of Sn droplets, compared to continuous growth. The crystal quality improved with the insertion of a GaN regrown layer prior to the pulsed-mode growth. The stoichiometric ZnSnGa2N4 alloy was achieved with a TMSn pulsing time of 15 s in the 1 min growth loop. The valence band offset (VBO) between ZnSnGa2N4 and GaN was determined experimentally via X-ray photoelectron spectroscopy to be 0.96 ± 0.10 eV. This value is in good agreement with the predicted value of 0.9 eV, assuming a linear dependence of the VBO on the alloy composition. The results from this work will provide additional design freedom based on III-N/II-IV-N2 heterostructures for electronic and optoelectronic devices.

Background carbon (C) impurity incorporation in metalorganic chemical vapor deposition (MOCVD) grown gallium nitride (GaN) represents one of the major issues in further improving GaN vertical power device performance. This work presents a laser-assisted MOCVD (LA-MOCVD) technique to address the high-C issue in MOCVD homoepitaxial GaN under different growth rate (Rg) regimes and studies the correlations between [C] and Rg. [C] in LA-MOCVD GaN is reduced by 50%–90% as compared to the conventional MOCVD GaN for a wide growth rate range between 1 and 16  μm/h. A mass-transport based model is developed to understand the C incorporation at different Rg regimes. The results obtained from the developed model are in good agreement with experimental data. The model further reveals that LA-MOCVD effectively suppresses C incorporation by reducing the active C species in the gas phase. Moreover, high step velocity in step flow growth mode can facilitate C incorporation at fast Rg, exhibiting steeper C increase. The theoretical model indicates that [C] can be suppressed below 1016 cm−3 with a fast growth rate (Rg) of 10  μm/h by utilizing higher power LA-MOCVD and freestanding GaN substrates with larger off-cut angles.

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