Study on electrical performance of AlGaN/GaN high electron mobility transistor based on cap layer design

This study investigates the impact of different cap layers on the electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs). By comparing the fabricated AlGaN/GaN HEMTs with GaN and AlN cap layers, it was found that AlN cap layer increases the two-dimensional electron gas (2DEG) density due to its superior passivation and polarization effects, yielding a higher saturation current and boosting breakdown voltage from 615 V (GaN) to 895 V (AlN). Sentaurus TCAD simulations confirm these findings, showing a deeper energy band triangular potential well in AlN-capped HEMTs, leading to a 2DEG electron density of 1.19 x 1013 cm-2, compared to 0.93 x 1013 cm-2 for GaN-capped HEMTs. The larger energy band gap of AlN cap layer provides a more effective potential barrier, reducing electric field intensity and increasing breakdown voltage. Additionally, the novel AlN-AlGaN-GaN and GaN-AlGaN-AlN graded cap layers are proposed to further enhance breakdown voltage, reaching up to 1308 V. These graded structures balance the electric field, block electron leakage, and improve electron transfer, providing a significant performance boost. This study underscores the potential of AlN and graded cap layers for future high-performance HEMTs.