Demonstration of Normally-Off N-Polar GaN Deep Recess HEMT

In this letter, we report the first normally-OFF N-polar GaN deep recess high electron mobility transistor (HEMT). Utilizing atomic layer etching (ALE), followed by acid treatment, we achieved normally-OFF operation through gate recess etching on an N-polar GaN deep recess HEMT epitaxial structure, with metal-organic chemical vapor deposition (MOCVD) SiNx serving as the gate insulator. A threshold voltage of +0.5 V was attained, along with impressive metrics, such as low OFF-state drain leakage current (12 nA/mm), OFF-state gate leakage current (28 nA/mm), and ON-state gate current (35 nA/mm). Remarkable performance parameters include a high on/off ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 10^{{7}}$ </tex-math></inline-formula>, drain OFF-state breakdown voltage of 53 V, and gate forward bias breakdown voltage of 5 V. Small signal measurements demonstrated a current-gain cutoff frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\text {T}}$ </tex-math></inline-formula>) and power-gain cutoff frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\mathbf {MAX}}$ </tex-math></inline-formula>) of 8.6 and 52.1 GHz, respectively, with a gate length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.6~\mu $ </tex-math></inline-formula> m. Furthermore, a competitive output power density of 5.1 W/mm with 50% power added efficiency was achieved at 4 GHz. Results underscore the potential of normally-off N-polar GaN deep recess HEMTs for both RF and high-voltage applications.