Enhancing electrical performance and E-mode operation of AlGaN channel MIS HEMTs through stacked-layer and multi-grade channel designs

This research investigates the performance of three distinct designs of AlGaN channel MIS HEMTs. The first device comprises a MIS HEMT with a high aluminum content AlGaN channel, the second design (SL-MIS HEMT) is the modified form of the first device with an Al0.1Ga0.9N – In0.15Ga0.85N - Al0.1Ga0.9N stacked-layer beneath the gate metal and the third design is a further modified form of the second design with multi-grade AlGaN channel (MG-MIS HEMT). This study's main objectives were to enhance the electrical performance of AlGaN channel MIS HEMTs and eventually enable the device to operate in E-mode. Notably, simulation results reveal a 19% increase in the maximum drain current density from 1.16 A/mm to 1.38 A/mm with the inclusion of stacked-layer under the gate in AlGaN channel MIS HEMTs. However, the MG-MIS HEMT design uniquely achieves E-mode operation, shifting the threshold voltage from -2.6 V (MIS-HEMT) to 0.18 V (MG-MIS HEMT). This comprehensive study delves into various linearity metrics or Figure of Merits (FOMs), including the 2nd-order and 3rd-order derivatives (g_m^'' and g_m^''') of drain current versus gate voltage, 2nd-order and 3rd-order intercept points (VIP2, VIP3) IIP3, and IMD3. The SL-MIS HEMT design demonstrates suitability for high linearity applications with higher VIP2, VIP3, and IIP3 values and lower IMD3 values. Similarly, the MG-MIS HEMT exhibits good linearity performance with lower g_m^'', g_m^''', and IMD3 values. Energy band diagrams, electron concentrations, electric field distributions, drain and transfer characteristics, and transconductance profiles are also evaluated.