Numerical Calculation of THz Emission of a GaN HEMT Using Coupled Hydrodynamic-Maxwell Equations

In this work, the characteristics of plasma oscillations in the two-dimensional electron gas in a GaN HEMT and its THz emission properties are studied using finite difference time domain method. Differentiation of the hydrodynamic equation satisfied by the two-dimensional electron fluids and Maxwell equations in two-dimensional space are conducted and coupled with each other. In order to reduce the calculation time and ensure the computational accuracy, the gradient non-uniform grids are adopted in the computational area. In the process of time iteration, different variables of the two-dimensional electron gas and electric and magnetic fields in two-dimensional plane are investigated, respectively. The coupling of the electric field in the two-dimensional space and current in two-dimensional gas are coupled together and the stable numerical results are obtained. The temporal dependence of the source areal current is studied and the areal current along the channel at different times are analyzed. At the end, the two-dimensional distribution of the power flow density generated by a GaN HEMT and its THz radiation power are obtained.