We present an analytical model for the I-V characteristics of AlGaN/GaN and AlInN/GaN high electron mobility transistors (HEMT). Our study focuses on the influence of a GaN capping layer, and of thermal and self-heating effects. Spontaneous and piezoelectric polarizations at Al (Ga,In)N/GaN and GaN/Al(Ga,In)N interfaces have been incorporated in the analysis. Our model permits to fit several published data. Our results indicate that the GaN cap layer reduces the sheet density of the two-dimensional electron gas (2DEG), leading to a decrease of the drain current, and that n+-doped GaN cap layer provides a higher sheet density than undoped one. In n+GaN/AlInN/GaN HEMTs, the sheet carrier concentration is higher than in n+GaN/AlGaN/GaN HEMTs, due to the higher spontaneous polarization charge and conduction band discontinuity at the substrate/barrier layer interface.
In this work the effects of technological and electrical parameters of Al m Ga 1-m N/GaN High Electron Mobility Transistors (HEMT) on the output conductance "g d " was studied in the first part. In the second part, the effect on g d of thermal and self heating in the device was analyzed. This study was made by taking into account the effects of spontaneous and piezoelectric polarizations in the heterojunction AlGaN/GaN and the relaxation of the crystal lattice induced by the aluminum mole fraction. An analytical model for the electrons concentration "n s " in the 2DEG and the current I ds in the channel for strong inversion regime was presented. By solving the Poisson equation and Schrödinger self-consistent calculations, including the spontaneous and piezoelectric polarizations, lattice relaxation, self heating and thermal effects the current I ds was calculated. The output conductance g d according to the voltage V ds are deduced thanks to the analytical description of the calculated current I ds .
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