  A high threshold voltage enhancement-mode GaN HEMT with p-type doped buffer
is discussed and simulated. Analytical expressions are derived to explain the
role of buffer capacitance in designing and enhancing threshold voltage.
Simulations of the proposed device with p-type buffer show threshold voltages
above 5 V, and a positive shift in threshold voltage as the oxide capacitance
is reduced, thus enabling threshold voltage tunability over an unprecedented
range for GaN-based HEMTs. The electric field profiles, breakdown performance,
on-resistance and delay tradeoffs in the proposed pGaN back HEMT device are
also discussed.
