Influence of Mg Out-Diffusion Effect on the Threshold Voltage of GaN-Based p-Channel Heterostructure Field-Effect Transistors

To resolve the parasitic problems and to fully leverage the superiority of GaN-based high electron mobility transistors, monolithic integration of different function blocks is a promising solution. The enhancement mode (E-mode) GaN-based p-channel heterostructure field-effect transistor (p-HFET) is one of the key components. Herein, the threshold voltage (V-TH) is modeled, and the influence of the Mg out-diffusion effect on V-TH is investigated. The impact of the diffusion coefficient of Mg, the Mg concentration in the p-GaN layer, the thicknesses of the AlGaN layer (t(b)), p-GaN channel layer (t(ch)), and an oxide layer (t(ox)) on V-TH are all taken into consideration for systematic exploration. The analysis illustrates that lower Mg concentration, smaller diffusion coefficient, and thinner p-GaN channel and AlGaN layers facilitate the realization of E-mode p-HFETs. Furthermore, it can be observed that lower Mg concentration in the p-GaN layer diminishes the V-TH sensitivity to the thickness of the p-GaN channel layer. Hence, a heterostructure with two p-GaN layers of different concentrations is suggested to reduce the complexity of the etching technique while improving the ohmic contacts. As a result, the model can effectively guide the design of GaN-based E-mode p-HFETs.