Gallium Nitride‐Based Lateral and Vertical Nanowire Devices

This chapter focuses on the first fabrication and characterization of GaN‐based lateral and vertical nanowire (NW) field‐effect transistors (FETs) by using top‐down approach, where one combined conventional e‐beam lithography and dry etching techniques with strong anisotropic tetramethyl ammonium hydroxide (TMAH) wet etching. Wet etching usually provides high etching selectivity that often offers an advantage in simplifying the fabrication process compared to the dry plasma etching. To fabricate the AlGaN/GaN O‐shaped‐gate nanowire FET, the GaN epitaxial layers were first grown on c‐plane sapphire substrate by MOCVD. The epitaxial structure of Si‐doped GaN/undoped‐GaN/Si‐doped GaN stack was grown by MOCVD on sapphire substrate. The AlGaN‐/GaN‐based omega‐gate NW FETs have been fabricated using TMAH orientation‐selective lateral wet etching of atomic layer‐deposited (ALD)‐deposited HfO₂ sidewall spacer. The top‐down approach provides a viable pathway toward gate‐all‐around (GAA) devices for III‐nitride semiconductors, which are very promising candidates for steep‐switching power device applications.