Analytical Modeling and Simulation of V/sub th/ and V/sub tl/ of the Delta-Doped MOS-Gate Si/SiGe HEMT

The delta-doped HEMT, a subcategory of HEMT, uses a thin layer of doping in the supply layer. There are quite a few advantages of the delta-doped HEMT over the regular-doped HEMT that include increase in mobility and cutoff frequency. The model for the threshold voltage of the delta-doped MOS-gate HEMT proposed by Gokhale et al. (1993) is valid only when the delta-doped layer is very thin and the distance of the layer from the SiO₂/Si interface is much larger than the thickness of the layer. Although, delta-doped HEMTs normally use a highly doped thin layer, varying the width of the layer, the threshold voltage, minimum gate voltage, transconductance, cut-off frequency etc. can be changed. In this paper, a model for the threshold voltage (V_th) and the minimum gate voltage (V_tl) of the p-channel delta-doped MOS-gate Si/SiGe HEMT is proposed which is valid for any thickness of the delta-doped layer. Also, the effect of the width of the delta-doped layer on the threshold voltage and the minimum gate voltage has been investigated using the analytical model. All results have been compared with Medicitrade simulation