DC Characteristics in High-Quality AlGaN/AlN/GaN High-Electron-Mobility Transistors Grown on AlN/Sapphire Templates

Abstract

High-crystal-quality Al0.26Ga0.74N/AlN/GaN structures with a very high mobility, such as over 2100 cm2/(V s) with a two-dimensional-electron gas (2DEG) density of approximately 1×1013/cm2, were grown on epitaxial AlN/sapphire templates by metalorganic vapor phase epitaxy and adopted for the fabrication of high-electron-mobility transistors (HEMTs). The fabricated devices showed good DC characteristics compared with those in conventional AlGaN/GaN HEMTs and in devices grown on sapphire substrates. Also, it was confirmed that further improvements in DC characteristics are achieved by applying recessed ohmic contacts to AlGaN/AlN/GaN HEMTs. A high extrinsic transconductance of approximately 220 mS/mm and a high drain current density of over 1 A/mm with a threshold voltage of -4.08 V were obtained for 1.5-µm-gate-length recessed ohmic AlGaN/AlN/GaN HEMTs on AlN/sapphire templates. In addition, it was found that the gate leakage current of HEMTs can be suppressed by using epitaxial AlN/sapphire templates as substrates.

Optimization of recessed ohmic contacts for AlGaN/AlN/GaN heterostructures using C(V) characterization of MSHM structures

“…The minimization of contact resistance relies on well controlled etching, a small over-or under etch will result in increased resistance [2]. AlGaN/AlN/GaN heterostructures are, generally, affected by even higher contact resistance than AlGaN/GaN heterostructures, and recessed ohmic contacts can be used to reduce contact resistance [3,4].…”

Trap states in n‐GaN grown on AlN/sapphire template by MOVPE

“…On the other hand, it was reported that high crystalline quality epitaxial AlN films grown on sapphire substrate at high temperature are promising template for GaN epitaxial growth [1]. The superior performance of GaNbased devices, high electron mobility transistor (HEMTs), grown on epitaxial AlN/sapphire template has also been shown [2][3][4]. Besides, an understanding of defects in these materials is essential for improving material quality and device performance.…”

Structural, morphological, and optical properties of AlGaN/GaN heterostructures with AlN buffer and interlayer

“…This is in agreement with recently reported results. 4,10 Additionally, the dislocation densities and rms roughness values of samples B and C grown on an AlN buffer/Al 2 O 3 template are found to be similar to each other. The AFM results clearly indicate that the AlN BL improves the top surface quality.…”

“…Recently, it has been reported that the crystal quality of GaN epitaxial films grown on an AlN buffer/Al 2 O 3 template is considerably improved. 10,11 On the other hand, the enhancement of two-dimensional electron-gas (2DEG) density and mobility in HEMTs has been more or less successful by different methods. For instance, an AlGaN ternary layer ͑TL͒ was doped with silicon in order to increase 2DEG density but this increase was rather limited.…”