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.

中文翻译：

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单晶 AlN 衬底上 N 极性 AlGaN/AlN 异质结构中的极化诱导二维电子气

极化诱导载流子在实现超宽带隙半导体 AlGaN 的高导电性方面发挥着重要作用，这对于从射频和电力电子到深紫外光子学的各种应用至关重要。尽管有重大的科学和技术兴趣，但对 N 极 AlGaN 中极化诱导载流子的研究很少。我们通过系统地改变 8 nm 顶层中的 Al 含量从 x = 0 到 x = 0.6，跨越从 3.56 到 4.77 eV 的能带隙。2DEG 密度随着 Al 含量的增加而单调下降，从 GaN 通道中的 3.8 × 1013/cm2 下降到 x = 0.6 时无法测量的电导率。对于 x = 0.49，合金散射将 2DEG 迁移率限制在 50 cm2/V s 以下。这些结果为在 AlN 上设计 N 极 AlGaN 沟道高电子迁移率晶体管提供了宝贵的见解，用于高压和高温下的极端电子产品，以及 UV 光子器件。