Enhancement-Mode GaN-Based High-Electron Mobility Transistors on the Si Substrate With a P-Type GaN Cap Layer

• Published in: IEEE transactions on electron devices 2014-02, Vol.61 (2), p.460-465
• Main Authors: Liang-Yu Su, Lee, Finella, Jian Jang Huang
• Format: Article
• Language: English
• Subjects: Aluminum gallium nitride; Channels; Enhancement mode (E-mode); Etching; Gallium nitride; GaN on Si; HEMTs; high-electron mobility transistors (HEMTs); Logic gates; MODFETs
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2013.2294337

An enhancement-mode (E-mode) high-electron mobility transistor (HEMT) was demonstrated by inserting a p-type GaN layer underneath the gate electrode. The effects of process flows and device structures on the electrical properties are investigated in this paper. We demonstrated a threshold voltage (Vth) of 4.3 V by adjusting the built-in voltage of the diode formed between the p-GaN and channel by the alloy temperature. Next, we found the existence of parallel conduction paths of the p-GaN layer and 2-D electron gas (2DEG) channel in such a HEMT structure. By removing p-GaN above the gate-source and gate-drain regions, current conduction migrates from p-GaN to 2DEG channel. The process window of the p-GaN residual thickness to ensure a steady forward current-voltage operation was estimated to be 10±5 nm in our case. Finally, with the p-GaN underneath the gate contact to deplete surface leakage current, an E-mode HEMT with a breakdown voltage (VBD) of 1630 V is achieved.