Sheet carrier concentration and threshold voltage modeling of asymmetrically doped AlGaN/GaN/AlGaN double heterostructure HEMT

An extensive analytical approach for the evaluation of threshold voltage and resultant sheet carrier density in a double-heterostructure AlGaN/GaN/AlGaN high electron mobility transistor (HEMT) has been presented in the paper. An asymmetrically doped structure is considered in the analysis in which the doping concentration of the donor-layers corresponding to the upper and lower heterostructure is taken to be different. Therefore, while the doping density of the donor layer in the lower heterostructure is kept constant, the doping density in the donor-layer of the upper heterostructure is varied. This provides an additional control over the net doping concentration and in turn better control over the resultant threshold voltage and sheet-carrier concentration developed in a double-heterostructure (DH) HEMT. The effect of donor-layer doping density on threshold voltage and sheet-carrier density of a DH-HEMT as compared to single-heterostructure HEMT is thoroughly studied in the present analysis. The results obtained from the analytical model are compared and found to agree reasonably well with that obtained using ATLAS device simulation, thereby validating the proposed model.