On the Charge Electron Control of the Two-Dimensional Gas for Analytic Modeling - of HEMT'S

Abstruct-A simple charge control model of the two-dimensional electron gas (ZDEG) of HEMT’s, which expliaUy take into account the effective distance of the 2-DEG from the heterointerface, has been developed for use in analytic I- Y and C- V modeling. In this model, the Fermi energy level versus the 2-DEG sheet carrier concentration is represented by a simplified expression derived from the triangular potential well approximation and is shown to be dominated by terms with different functional forms in two distinct operation regions: a moderate carrier concentration region and a subthreshold region. The validity of the analytic charge control model is supported by the calculated results of self-consistent quantum mechanical model. I. INTRODUCTION HE recent development of the HEMT, employing novel T layer structures such as strained-layer heterostructures, has shown a promise of higher transconductance and a good power capability resulting from superior electronic transport properties of the active channel, a larger sheet carrier concentration, and better confinement at the heterointerface. These enhanced characteristics lead to improved device performance which demands a more accurate approximation of the charge control model over a wider operation range in order to obtain accurate HEMT I- V and C- V models useful for circuit simulators. The analytic models most widely used for characterizing HEMT performance are based on the linear charge control model [l], [2], which either neglects the variation of the Fermi potential with the gate bias, or for simplicity, assumes a constant correction distance in the direction normal to the heterointerface plane accounting for the quantization of the two-dimensional electron gas (2-DEG) in the quasi-triangular potential well. These assumptions only hold for a very narrow range and result in a low degree of accuracy in the model when device behavior is characterized over the whole operation region. Recently, Kola et al. [3] proposed a data fitting expression for Fermi level versus sheet carrier concentration that would take into consideration the modulation effect of an applied bias on the Fermi energy. However, the expression lacks corresponding physical significance and requires a sophisticated data fitting process. In this study, we developed a simple yet more accurate Fermi energy expression, derived from the triangular