Two-dimensional numerical simulation of Fermi-level pinning phenomena due to DX centers in AlGaAs/GaAs HEMTs

Fermi-level pinning phenomena due to DX centers in AlGaAs/GaAs HEMTs (high electron mobility transistors) are analyzed using two-dimensional numerical simulation based on a drift-diffusion model. A DX center model is introduced assuming Fermi-Dirac statistics for ionized donor density with the aluminum mole fraction dependence of the deep-donor energy level. The calculated results reveal that the decrease in transconductance of AlGaAs/GaAs HEMTs in a high-gate-bias region is caused by the existence of DX centers. This is because the Fermi level is pinned at deep-donor levels in the n-AlGaAs layer. Furthermore, the superiority of AlGaAs/InGaAs pseudomorphic HEMTs is discussed in terms of the Fermi-level pinning