Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 1017 cm−3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (EC − 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm2/V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices.

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In this Letter, we demonstrate hybrid GaN lateral Schottky barrier diodes with enhanced breakdown characteristics and a low turn-on voltage. These diodes incorporate a lateral Schottky barrier in combination with a high permittivity material beneath the field plate, enabling high average breakdown fields and a low turn-on voltage. Average electric fields up to 2.38 MV/cm were achieved for devices with an anode–cathode spacing of 4 μm, while maintaining with a turn-on voltage of 0.48 V. In contrast, SiNx/AlGaN/GaN control lateral Schottky diodes displayed an average breakdown field of ∼0.7 MV/cm for devices with similar dimensions with a turn-on voltage of 0.46 V. The use of a high-permittivity dielectric can more effectively utilize the high breakdown fields in wide bandgap materials by proper management of the electric field. This demonstration provides an innovative way to integrate high-permittivity materials with GaN lateral devices for improved breakdown and resistance characteristics.

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In this Letter, we discuss AlGaN/GaN HEMTs integrated with high permittivity BaTiO3 dielectric to enable enhanced breakdown characteristics. We show that using high permittivity BaTiO3 dielectric layers in the gate and drain access regions prevents premature gate breakdown, leading to average breakdown fields exceeding 3 MV/cm at a gate-to-drain spacing of 4 μm. The higher breakdown fields enable a high power figure of merit above 2.4 GW/cm2 in devices with a gate-to-drain spacing of 6 μm. This work demonstrates that electrostatic engineering using high-permittivity dielectrics can enable AlGaN/GaN HEMTs in approaching the material breakdown field limits.