Drain E-Field Manipulation in AlGaN/GaN HEMTs by Schottky Extension Technology

The proposed hybrid Schottky–ohmic drain structure is analyzed in detail for AlGaN/GaN power high-electron mobility transistors on the Si substrate. Without any additional photomasks and process steps, the hybrid drain design can alter the electric field distribution to improve the breakdown voltage $V_{\rm BK}$ . In addition, it provides an additional current path to achieve zero onset voltage and reduce the ON-resistance. It was found that the Schottky extension $L_{\rm ext}$ is critical to $V_{\rm BK}$ , $R_{{\mathrm{{\scriptstyle ON}}}}$ , and also the current collapse phenomena of the transistors. The extended Schottky electrodes for optimized transistor characteristics are investigated, and the physics behind are discussed. With an $L_{\rm ext}\sim 2$ –3 $\mu $ m, $V_{\rm BK}$ can be improved up to 60% with an $R_{{\mathrm{{\scriptstyle ON}}}}$ degradation below 3%.