Polarization-induced 2D electron gases in N-polar AlGaN/AlN heterostructures on single-crystal AlN substrates

Abstract

Polarization-induced carriers play an important role in achieving high electrical conductivity in ultrawide bandgap semiconductor AlGaN, which is essential for various applications ranging from radio frequency and power electronics to deep UV photonics. Despite significant scientific and technological interest, studies on polarization-induced carriers in N-polar AlGaN are rare. We report the observation and properties of polarization-induced two-dimensional electron gases (2DEGs) in N-polar AlGaN/AlN heterostructures on single-crystal AlN substrates by systematically varying the Al content in the 8 nm top layers from x = 0 to x = 0.6, spanning energy bandgaps from 3.56 to 4.77 eV. The 2DEG density drops monotonically with increasing Al content, from 3.8 × 1013/cm2 in the GaN channel, down to no measurable conductivity for x = 0.6. Alloy scattering limits the 2DEG mobility to below 50 cm2/V s for x = 0.49. These results provide valuable insights for designing N-polar AlGaN channel high electron mobility transistors on AlN for extreme electronics at high voltages and high temperatures, and for UV photonic devices.

Density Functional Theory Study of Polarization-Induced Electron Confinement by Dilute Boron Alloying in ε-Ga2O3 Nanometer-Thick Film for High Electron Mobility Transistor

“…Ga 2 O 3 possesses five polymorphs, specifically α, β, γ, δ, and ε. Among these, the ε-phase is noted for its remarkable polarization property, which is an order of magnitude greater than GaN, a semiconductor material typically employed in high electron mobility transistors (HEMTs). , The findings on polarization of ε-phase Ga 2 O 3 have piqued the interest of numerous researchers that are exploring the possibilities of ε-Ga 2 O 3 based devices. − Chen et al have reported on the polarization switching properties of κ-Ga 2 O 3 (where κ and ε denote the same phase of Ga 2 O 3 ) in κ-Ga 2 O 3 /GaN heterostructure, revealing a remanent polarization of approximately 2.7 μC/cm 2 . Wang et al have indicated that the interface of ε-Ga 2 O 3 / m -GaN ( m -AlN) could achieve a high two-dimensional electron gas (2DEG) density of 10 14 cm –2 .…”