We report on room temperature terahertz generation by a submicron size AlGaN/GaN-based high electron mobility transistors. The emission peak is found to be tunable by the gate voltage between 0.75 and 2.1 THz. Radiation frequencies correspond to the lowest fundamental plasma mode in the gated region of the transistor channel. Emission appears at a certain drain bias in a thresholdlike manner. Observed emission is interpreted as a result of Dyakonov–Shur plasma wave instability in the gated two-dimensional electron gas.

We report on AlGaN/GaN heterostructures and heterostructure field-effect transistors (HFETs) fabricated on high-pressure-grown bulk GaN substrates. The $\text{2d}$ electron gas channel exhibits excellent electronic properties with room-temperature electron Hall mobility as high as $\text{μ=1650\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V s}$ combined with a very large electron sheet density $n_s{\text{≈1.4×10}}^{13} {\mathrm{cm}}^{\mathrm{-2}}.$ The HFET devices demonstrated better linearity of transconductance and low gate leakage, especially at elevated temperatures. We also present the comparative study of high-current AlGaN/GaN HFETs ${\mathrm{(n}}_s{\text{μ>2×10}}^{16} {\mathrm{V}}^{\mathrm{-1}}{\mathrm{ s}}^{\mathrm{-1}}\mathrm{)}$ grown on bulk GaN, sapphire, and SiC substrates under the same conditions. We demonstrate that in the high-power regime, the self-heating effects, and not a dislocation density, is the dominant factor determining the device behavior.

We have investigated the aging processes in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals. The measured threshold current turned out to be a square root function of aging time, indicating the importance of diffusion for device degradation. The differential efficiency, in contrast, was roughly constant during these experiments. From these two observations we can conclude that the main reason for degradation is the diffusion-enhanced increase of nonradiative recombination within the active layer of the laser diode. Additionally, microscopic studies of the degraded structures did not reveal any new dislocations within the active area of the aged diodes, thus identifying point defects as a source of nonradiative processes.

This paper reports on the evolution of the structural and electrical proprieties of Au/Ni contacts to p-type gallium nitride (GaN) upon thermal treatments. Annealing of the metals in an oxidizing atmosphere (N₂/O₂) led to better electrical characteristics, in terms of specific contact resistance (ρ_c), with respect to non-reacting ambient (Ar). The evolution of the metal structures and the formation of a NiO layer both at the sample surface and at the interface with p-GaN were monitored by several techniques such as transmission electron microscopy (TEM), x-ray diffraction (XRD), and atomic force microscopy (AFM). Furthermore, a reduction of the Schottky barrier height from 1.07 eV (Ar annealing) to 0.71 eV (N₂/O₂ annealing) was determined by the temperature dependence of the ρ_c. Local current maps by conductive AFM demonstrate the role of the interface in the conduction mechanism. These electrical results were correlated with the interfacial microstructure of the annealed contacts considering different transport models.

We have measured the temperature dependence of the mobility of the two-dimensional electron gas in AlGaN/GaN heterostructures grown on bulk GaN substrates. The linear dependence of the inverse mobility on temperature at temperatures below 50 K indicates the importance of acoustic phonon scattering in these high mobility heterostructures. Using the temperature dependence of the mobility at a range of carrier densities, we determined the GaN conduction band deformation potential to be $a_c\text{=9.1±0.7\hspace{0.17em}}\mathrm{eV}.$ This result provides a crucial parameter for accurate calculations of intrinsic mobility limits in AlGaN/GaN heterostructures.