Extraction of FET parameters at low drain bias by taking into account the dependence of mobility on 2D electron gas concentration

An original method for the extraction of FET parameters at low drain bias is presented. It is based on a simple linear charge-control model and on a power-law dependence (with an exponent k ≫ 0 for GaAs/AIGaAs MODFET´s and k ≪ 0 for Si-MOSFET´s) of the low-field mobility ¿ on the two-dimensional electron gas (2DEG) concentration nS, valid in a cerain range of gate voltages. Simple analytical expressions for the transfer characteristics Ids-Vgs and gm-Vgs at low drain bias are combined to extact reliable values of the threshold voltage Vt, the power exponent k, the total parasitic series resistance (Rs+Rd) and an important control parameter ß´. We verified that the values of ß´ and k extracted on a test MODFET at 300 and 77 K agree very well with those deduced directly from Hall measurements on gated Hall-bridge structures. Our analysis is also applied to extract MOSFET parameters at room temperature.