Improvements in characteristics of N-polar Si-doped AlGaN epi-layer grown on mis-oriented c-plane sapphire substrate

Xu, Shenyu; Zhang, Xiong; Luo, Xuguang; Fang, Ruiting; Lyu, Jiadong; Lai, Mu-Jen; Hu, Guohua

doi:10.1016/j.mssp.2023.107447

Materials Science in Semiconductor Processing

2023

DOI: 10.1016/j.mssp.2023.107447

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Improvements in characteristics of N-polar Si-doped AlGaN epi-layer grown on mis-oriented c-plane sapphire substrate

Shenyu Xu

Xiong Zhang

Xuguang Luo

et al.

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Cited by 3 publications

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Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

Mondal,

Wang,

Anhar Uddin Bhuiyan

et al. 2023

Applied Physics Letters

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N-polar AlGaN is an emerging wide-bandgap semiconductor for next-generation high electron mobility transistors and ultraviolet light emitting diodes and lasers. Here, we demonstrate the growth and characterization of high-quality N-polar AlGaN films on C-face 4H-silicon carbide (SiC) substrates by molecular beam epitaxy. On optimization of the growth conditions, N-polar AlGaN films exhibit a crack free, atomically smooth surface (rms roughness ∼ 0.9 nm), and high crystal quality with low density of defects and dislocations. The N-polar crystallographic orientation of the epitaxially grown AlGaN film is unambiguously confirmed by wet chemical etching. We demonstrate precise compositional tunability of the N-polar AlGaN films over a wide range of Al content and a high internal quantum efficiency ∼74% for the 65% Al content AlGaN film at room temperature. Furthermore, controllable silicon (Si) doping in high Al content (65%) N-polar AlGaN films has been demonstrated with the highest mobility value ∼65 cm2/V-s observed corresponding to an electron concentration of 1.1 × 1017 cm−3, whereas a relatively high mobility value of 18 cm2/V-s is sustained for an electron concentration of 3.2 × 1019 cm−3, with an exceptionally low resistivity value of 0.009 Ω·cm. The polarity-controlled epitaxy of AlGaN on SiC presents a viable approach for achieving high-quality N-polar III-nitride semiconductors that can be harnessed for a wide range of emerging electronic and optoelectronic device applications.

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Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

Mondal,

Wang,

Anhar Uddin Bhuiyan

et al. 2023

Applied Physics Letters

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Achieving semi-metallic conduction in Al-rich AlGaN: Evidence of Mott transition

Mondal,

Kezer,

Wang

et al. 2024

Applied Physics Letters

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The development of high performance wide-bandgap AlGaN channel transistors with high current densities and reduced Ohmic losses necessitates extremely highly doped, high Al content AlGaN epilayers for regrown source/drain contact regions. In this work, we demonstrate the achievement of semi-metallic conductivity in silicon (Si) doped N-polar Al0.6Ga0.4N grown on C-face 4H-SiC substrates by molecular beam epitaxy. Under optimized conditions, the AlGaN epilayer shows smooth surface morphology and a narrow photoluminescence spectral linewidth, without the presence of any secondary peaks. A favorable growth window is identified wherein the free electron concentration reaches as high as ∼1.8 × 1020 cm−3 as obtained from Hall measurements, with a high mobility of 34 cm2/V·s, leading to a room temperature resistivity of only 1 mΩ·cm. Temperature-dependent Hall measurements show that the electron concentration, mobility, and sheet resistance do not depend on temperature, clearly indicating dopant Mott transition to a semi-metallic state, wherein the activation energy (Ea) falls to 0 meV at this high value of Si doping for the AlGaN films. This achievement of semi-metallic conductivity in Si doped N-polar high Al content AlGaN is instrumental for advancing ultrawide bandgap electronic and optoelectronic devices.

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Two-Dimensional Electron Gas in Thin N-Polar GaN Channels on AlN on Sapphire Templates

Pristovsek,

Furuhashi,

Yang

et al. 2024

Crystals

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We report on 2-dimensional electron gases realized in binary N-polar GaN channels on AlN on sapphire templates grown by metal–organic vapor phase epitaxy. The measured sheet carrier density of 3.8×1013 cm−2 is very close to the theoretical value of 3.95×1013 cm−2 due to the low carbon and oxygen background doping in the N-polar GaN if grown with triethyl-gallium. By inserting an intermediate AlN transition layer, room temperature mobilities in 5 nm channels up to 100 cm2/Vs were realized, probably limited by dislocations and oxygen background in N-polar AlN. Thicker channels of 8 nm or more showed relaxation and thus much lower mobilities.

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Improvements in characteristics of N-polar Si-doped AlGaN epi-layer grown on mis-oriented c-plane sapphire substrate

Cited by 3 publications

References 18 publications

Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

Achieving semi-metallic conduction in Al-rich AlGaN: Evidence of Mott transition

Two-Dimensional Electron Gas in Thin N-Polar GaN Channels on AlN on Sapphire Templates

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