Impact of an Underlying 2DEG on the Performance of a p-Channel MOSFET in GaN

The influence of an underlying 2-dimensional electron gas (2DEG) on the performance of a normally off p-type metal oxide semiconductor field effect transistor (MOSFET) based on GaN/AlGaN/GaN double heterojunction is analyzed via simulations. By reducing the concentration of the 2DEG, a greater potential can be dropped across the GaN channel, resulting in enhanced electrostatic control. Therefore, to minimize the deleterious impact on the on-state performance, a composite graded back-to-back AlGaN barrier that enables a trade-off between n-channel devices and Enhancement-mode (E-mode) p-channel is investigated. In simulations, a scaled p-channel GaN device with L_G = 200 nm, L_SD = 600 nm achieves an I_ON of 65 mA/mm, an increase of 44.4% compared to a device with an AlGaN barrier with fixed Al mole fraction, I_ON/I_OFF of ∼10¹², and |V_th| of | - 1.3 V|. For the n-channel device, the back-to-back barrier overcomes the reduction of I_ON induced by the p-GaN gate resulting in an I_ON of 860 mA/mm, an increase of 19.7% compared with the counterpart with the conventional barrier with 0.5 V positive V_th shift.