OPTIMIZATION IN CONVENTIONAL COMPOSITE RECESSED STRUCTURED HEMT

Abstract

The present thesis delves into the latest developments in High-Electron-Mobility Transistors (HEMTs), emphasizing the improvement of both the breakdown voltage (Vbr) and threshold voltage (Vth). Several methods for modulating electric fields and lowering parasitic unwanted current are explored, including the use of composite step- like design gate structures with p-GaN buried layers. Further research is done on double AlGaN barrier designs, showing that reducing the amount of Al in the bottom barrier can lower 2DEG density and improve gate control, which raises Vth. The performance of enhancement - mode HEMTs is further enhanced by optimizations including graded AlGaN barriers, recessed gate designs, p-GaN caps, and the addition of dielectric layers like Al3O₃. These methods ensure acceptable transconductance and saturation current while striking a compromise between high threshold voltage (switching voltage) and breakdown voltage. The development of enhancement-mode GaN based HEMTs with elevated threshold voltage is crucial for reliable and safe power electronic systems. In this work, a novel composite recessed-gate HEMT with an integrated stepped channel structure is proposed, combining the advantages of both recessed gate engineering and channel modulation. The integration of Al2O3 on the recessed p-GaN region boosts Vth, but typically at the cost of reduced saturation current Isat and transconductance gm. By embedding a stepped channel within the composite recessed gate, the proposed device achieves a superior balance of high Vth. Simulation results demonstrate that the optimized structure achieves a Vth of 5.7 V, over conventional recessed p-GaN HEMTs with Al2O3 and the device achieves a breakdown voltage of 1250V. The electric field distribution is significantly improved, and leakage current is suppressed. These results indicate that the composite recessed-gate HEMT with a stepped channel and field modulation offers a promising solution for next-generation high power and RF GaN device applications.