A new I-V model for short gate-length MESFET's operated in the turn-on region is proposed, in which the twodimensional potential distribution contributed by the depletion-layer charges under the gate and in the ungate region are separately obtained by conventional 1D approximation and Green's function solution technique. Moreover, the bias-dependent parasitic resistances due to the modulation of depletion layer in the ungate region for non-self-alignment MESFET's are also taken into account in the developed I-V model. It is shown that good agreements are obtained between the developed new I-V model and the results of 2D numerical analysis. Moreover, comparisons between the proposed analytical model and the experimental data are made and excellent agreements are obtained. NOMENCLATURE Dielectric permittivity of semiconductor. Elemental charge (= 1.6 X Active-layer thickness. Gate length. Spacing between the gate and the drain (source). Built-in potential of Schottky-barrier gate. Gate-source voltage. Drain-source voltage. Two-dimensional potential distribution. Component of the two-dimensional potential distribution contributed by the depletion charge under the gate. Component of the two-dimensional potential distribution contributed by the depletion charge in the ungate region. C). Electron-density distribution. Doping profile. Potential distribution along the channel (= Electric field distribution along the channel Drift velocity of electrons. Parasitic series resistance at the source(drain) Wx, b)).
A new analytical technique for calculating the twodimensional (2D) potential distribution of a MESFET device operated in the subthreshold region is proposed, in which the 2D Poisson's equation is solved by the Green's function technique. The potential and electric-field distributions of a nonself-aligned MESFET device are calculated exactly from different types of Green's function in different boundary regions, and the sidewall potential at the interface between these regions can be determined by the continuation of the electric field at the sidewall boundary. The remarkable feature of the proposed method is that the implanted doping profile in the active channel can be treated. Furthermore, a simplified technique is developed to derive a set of quasi-analytical models for the sidewall potential at both sides of the gate edge, the threshold voltage of short gate-length devices, and the drain-induced barrier lowering. Moreover, the developed quasi-analytical models are compared with the results of 2D numerical analysis and good agreements are obtained.
B mFourier coefficient for the one-dimensional (1D) potential distribution produced by the ionized impurity concentration. Fourier coefficient for the doping profile in the ungate region at the source side N;,.(x) c = l f o r n = O a n d c = 2 f o r n ? 1 . Fourier coefficient for the doping profile in ) N&(x) the ungate region at the drain side NOMENCLATURE c = l f o r n = O a n d c = 2 f o r n 2 1 \k(x, y) Two-dimensional (2D) potential distribution. E
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