This brief aims to show the effects of threading edge dislocations on the dc and RF performance of GaN highelectron mobility transistor (HEMT) devices. A state-of-the-art high-frequency and high-power HEMT was investigated with our full-band cellular Monte Carlo (CMC) simulator, which includes the full details of the band structure and the phonon spectra. A complete characterization of the device has been performed using experimental data to calibrate the few adjustable parameters of the simulator. Thermal simulations were also carried out with commercial software in order to operate the corrections needed to model thermal effects. The approach of Weimann based on the results of Read, Bonch-Bruevich and Glasko, and Pödör was then used to model with our CMC code the dislocation effects on the transport properties of HEMT devices. Our simulations indicate that GaN HEMT performance exhibits a fairly large dependence on the density of thread dislocation defects. Furthermore, we show that a threshold concentration exists, above which a complete degradation of the device operation occurs.

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Here we report on high field transport in GaN based on the rigid ion model of the electron-phonon interaction within the cellular Monte Carlo (CMC) approach. Using the rigid pseudo-ion method for the cubic zinc-blende and hexagonal wurtzite structures, the anisotropic deformation potentials are derived from the electronic structure, the atomic pseudopotential and the full phonon dispersion and eigenvectors for both acoustic and optical modes. Several different electronic structure and lattice dynamics models are compared, as well as different models for the interpolation of the atomic pseudopotentials required in the rigid pseudo-ion method. Piezoelectric as well as anisotropic polar optical phonon scattering is accounted for as well. In terms of high field transport, the peak velocity is primarily determined by deformation potential scattering described through the rigid pseudo-ion model. The calculated velocity is compared with experimental data from pulsed I-V measurements. Good agreement is found using the rigid ion model to the measured velocity-field characteristics with the inclusion of dislocation and ionized impurity scattering. The crystal orientation of the electric field is investigated, where very little difference is observed in the velocity-field characteristics. We simulate the effects of nonequilibrium hot phonons on the energy relaxation as well, using a detailed balance between emission and absorption during the simulation, and an anharmonic decay of LO phonons to acoustic phonons, as reported previously. Nonequilibrium phonons are shown to result in a significant degradation of the velocity-field characteristics for high carrier densities, such as those encountered at the AlGaN/GaN interface due to polarization effects.

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We utilize a 3D full-band Cellular Monte Carlo (CMC) device simulator to model ultrashort gate length pseudomorphic high-electron-mobility transistors (p-HEMTs). We present the static dc device characteristics and rf response for gate lengths ranging from 10 nm to 50 nm. Preliminary passive results using 3D full-wave Maxwell solver are also presented to illustrate the usefulness of and insight that a future coupled full-band/full-wave simulator will provide in more accurately, modeling the high frequency performance of p-HEMTs.