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The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 10 4 times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN-and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects.

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Selectively activated p-type regions are necessary for many electronic devices that require planar processing. The standard process of implanting p-type dopants, such as Mg, in GaN is notoriously more difficult than in other material systems, as the extremely high temperatures required to activate the implanted Mg also damage the GaN surface. In this research, a novel annealing technique is introduced for this purpose -symmetric multicycle rapid thermal annealing (SMRTA). It is shown that SMRTA is superior to the earlier developed multicycle rapid thermal annealing (MRTA) in terms of improvement of the crystalline quality of implanted GaN. The SMRTA technique was applied to Mg-implanted GaN to realize a rectifying junction. The annealing process detailed in this research will be a key enabling step for future GaN-based GaN and other III-nitride based semiconductors have received a great deal of attention from the research community due to favorable material properties which include a tunable direct bandgap, radiation hardness, and a favorable Baliga figure of merit compared to Si and SiC.1,2 The doping of p-type GaN during growth is challenging and has been the focus of numerous studies because it has many potential transformative applications in power electronics and optoelectronics.3 P-type dopant implantation and activation adds additional complexity to the synthesis of p-type GaN. The ability to implant and activate p-type species in GaN is a key enabling process for devices that require selective area doping. Device structures that benefit from the ability to selectively implant and activate p-type dopants in GaN include implanted guard rings for electric field spreading, implanted current blocking layers for current aperture vertical electron transistors, and implanted regions below contacts to lower contact resistance. 4,5 Unfortunately, the implantation and activation of Mg in GaN is difficult because of the high temperatures required (over 1300• C) for the activation anneal, 6 which are significantly higher than the decomposition temperature of GaN at atmospheric pressures (845 • C). 7 The decomposition of GaN occurs due to a loss of nitrogen and results in surface damage and the formation of N vacancies, which are compensating donors. 8To avoid GaN decomposition at the elevated annealing temperatures required for Mg activation, high pressure environments and non-equilibrium annealing conditions combined with capping layers have been investigated. 9,10 GaN can be successfully annealed at about 1500• C, but a 1.5 GPa overpressure of N 2 is necessary to avoid surface degradation.11 Such high gas pressures also require a complicated experimental setup and are not easily industrial scalable. 12A second, more scalable, alternative to the high pressure annealing of GaN relies on using non-equilibrium annealing conditions. For this type of annealing, a capping layer is used to prevent nitrogen loss from the GaN surface. Depending on the material, structure, and thickness of the capping layer, higher annealin...

An Mg‐implanted p–i–n diode was fabricated and characterized. Mg activation was achieved using the multicycle rapid thermal annealing technique with rapid heating pulses up to 1340 °C. The surface of the implanted GaN after annealing was smooth (0.94 nm RMS roughness) with growth steps evident as characterized by atomic force microscopy. The full width at half‐maximum of the implanted GaN E2 Raman mode approaches that of the as‐grown GaN after the annealing process, indicating that the annealing process is able to reverse most of the implantation damage. The Mg‐implanted p–i–n diode exhibits rectification and a low leakage current of 0.11 μA cm−2 at a bias of −10 V. Under forward bias, light emission was observed from the p–i–n diode. The implantation and activation of Mg in a GaN‐based device, demonstrated for the first time in this research, is a key enabling step for future optoelectronic and power electronic devices. Current–voltage characteristics of the Mg‐implanted p–i–n diode with an inset of the device schematic.

The growth of InGaN alloys via Metal-Modulated Epitaxy has been investigated. Transient reflection high-energy electron diffraction intensities for several modulation schemes during the growth of 20% InGaN were analyzed, and signatures associated with the accumulation, consumption, and segregation of excess metal adlayers were identified. A model for shuttered, metal-rich growth of InGaN was then developed, and a mechanism for indium surface segregation was elucidated. It was found that indium surface segregation only occurs after a threshold of excess metal is accumulated, and a method of quantifying this indium surface segregation onset dose is presented. The onset dose of surface segregation was found to be indium-composition dependent and between 1 and 2 monolayers of excess metal. Below this surface threshold off excess metal, metal-rich growth can occur without indium surface segregation. Since at least 2 monolayers of excess metal will accumulate in the case of metal-rich, unshuttered growth of InGaN at the low temperatures required to suppress thermal and spinodal decomposition, this study reveals that some form of modulation must be employed to maintain this adlayer thickness. These theories were applied in the growth of InGaN with varying compositions using Metal-Modulated Epitaxy. Single-phase, high-quality InGaN films with compositions throughout the miscibility gap with root mean square roughnesses less than 0.8 nm were obtained, demonstrating the feasibility of shuttered, metal-rich InGaN growth.