Low specific on-resistance GaN-based vertical heterostructure field effect transistors with nonuniform doping superjunctions*

A novel GaN-based vertical heterostructure field effect transistor (HFET) with nonuniform doping superjunctions (non-SJ HFET) is proposed and studied by Silvaco-ATLAS, for minimizing the specific on-resistance (R on A) at no expense of breakdown voltage (BV). The feature of non-SJ HFET lies in the nonuniform doping concentration from top to bottom in the n- and p-pillars, which is different from that of the conventional GaN-based vertical HFET with uniform doping superjunctions (un-SJ HFET). A physically intrinsic mechanism for the nonuniform doping superjunction (non-SJ) to further reduce R on A at no expense of BV is investigated and revealed in detail. The design, related to the structure parameters of non-SJ, is optimized to minimize the R on A on the basis of the same BV as that of un-SJ HFET. Optimized simulation results show that the reduction in R on A depends on the doping concentrations and thickness values of the light and heavy doping parts in non-SJ. The maximum reduction of more than 51% in R on A could be achieved with a BV of 1890 V. These results could demonstrate the superiority of non-SJ HFET in minimizing R on A and provide a useful reference for further developing the GaN-based vertical HFETs.