Two-dimensional hydrodynamic modelling of AlGaN/GaN transistor-based THz detectors

Here, we report on numerical modelling of AlGaN/GaN HEMT terahertz detectors using a two-dimensional solver based on three Boltzmann transport equation (BTE) moments and the Poisson equation. We use the Synopsys TCAD Sentaurus program package, which offers a wide material database and the possibility to include traps and polarization charges for the formation of the channel without any doping. The implications of different levels of model simplifications are addressed both analytically and numerically. We calculated the current responsivity R, to THz radiation on the drain voltage in the frequency range 0.01-3.0 THz for three AlGaN layer thicknesses d= 15, 20 and 25 nm and different gate lengths. We demonstrate that only a hydrodynamic model can reproduce the change in the sign in current responsivity at the gate voltage UG9 (R1 = 0 at UG = UG0). The energy flux factor in the energy balance equation determines this effect. For the simulated structures, we find that the noise equivalent power may be as low as 0.1 pW/VHz at 0.04 THz and 10 pW/VHz at 3.0 THz.