N-polar III-nitride transistors

Wong, Man Hoi; Mishra, Umesh K.

doi:10.1016/bs.semsem.2019.08.012

Cited by 14 publications

(10 citation statements)

References 258 publications

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“…Surface morphology evolution as a function of growth time provides a clearer insight of the growth kinetics of N-polar GaN. Earlier reports have suggested that the ideal growth conditions for PA-MBE growth of Ga-and N-polar GaN layers are similar, which is the metal-rich regime [45]. The Ga-metallic layer that forms on the growing surface reduces the diffusion barrier for adatoms, hence promoting step-flow growth.…”

Section: Surface Morphology Evolution As a Function Of Growth Timementioning

confidence: 99%

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

Huo¹,

Lingaparthi²,

Dharmarasu³

et al. 2023

J. Phys. D: Appl. Phys.

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The surface morphology evolution of N-polar GaN with growth time was investigated and compared with Ga-polar GaN. N-polar GaN directly grown on SiC substrates was found to have slower three-dimensional (3D) to two-dimensional (2D) growth transformation and lesser coalescence than the Ga-polar counterpart, resulting in rougher surface morphology, whereas the AlN nucleation layer (NL) accelerated 3D to 2D transformation, resulting in smoother surface morphology. N-polar GaN was found to have mound-type surface morphology with clustered atomic steps, unlike the regular screw-type dislocation-mediated step-flow growth observed for Ga-polar GaN. This was explained by the lower diffusion of adatoms on the N-polar surface due to its higher surface energy and higher Ehrlich-Schwoebel barrier (ESB). In addition, the increased III/V ratio in N-polar GaN growth was found to reduce the surface roughness from 2.4 nm to 1 nm. Without Si doping, the N-polar GaN HEMT heterostructures grown under optimized conditions with smoother surface morphologies exhibited sheet carrier density of 0.91 × 1013 cm-2 and mobility of 1220 cm2/V∙s. With Si δ-doping, the sheet carrier density was increased to 1.28 × 1013 cm-2 while the mobility was reduced to 1030 cm2/V∙s. These results are comparable to the state-of-the-art data of PA-MBE-grown N-polar GaN HEMT heterostructures on SiC substrates.

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Section: Surface Morphology Evolution As a Function Of Growth Timementioning

confidence: 99%

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

Huo¹,

Lingaparthi²,

Dharmarasu³

et al. 2023

J. Phys. D: Appl. Phys.

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“…Besides, the N-polar GaN is easier to be manufactured into the enhancement mode transistors and the N-polar HEMTs have the advantage over Ga-polar HEMTs when they are scaled down. [18] Nevertheless, a high density of hexagonal hillocks appeared on the surface of the N-polar GaN layer grown on the C-plane sapphire by MOCVD. [19] The N-polar GaN without the hexagonal hillocks on the surface was grown by Matsuoka et al [20] on the C-plane sapphire by MOCVD and it showed the surface and a small full width at half maximum (FWHM) of the x-ray rocking curves for the (000 2) reflection.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the N-polar GaN film grown on C-plane sapphire and misoriented C-plane sapphire substrates by MOCVD

Hu¹,

Song²,

Su³

et al. 2022

Chinese Phys. B

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Gallium nitride (GaN) thin film of the nitrogen polarity (N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition (MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2° and 4° respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide (KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the X-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the X-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length. The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is near to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.

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“…For example, N-polar AlGaN DUV LEDs have better carrier injection efficiency and alleviated electron overflow than the Al-polar ones . N-polar AlGaN HEMTs are envisioned to have merits of high back-barrier, low ohmic contact resistivity, and flexible device scaling. − Moreover, the lateral-polarity structure, where N-polar and Al-polar domains are deposited periodically side by side in plane, shows great potential in fabricating DUV LEDs with higher radiation combination rate, and waveguides for generating second-harmonic . High-quality N-polar AlN templates are vital to achieve efficient N-polar Al-rich AlGaN-based devices due to the lack of native AlGaN substrates.…”

Section: Introductionmentioning

confidence: 99%

Unexpected Realization of N-Polar AlN Films on Si-Face 4H–SiC Substrates Using RF Sputtering and High-Temperature Annealing

Zhang

Guo

Cai

et al. 2023

Crystal Growth & Design

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In this study, we demonstrated AlN films with unexpected N-polarity on Si-face 4H−SiC substrates using RF reactive magnetron sputtering and post high-temperature annealing (HTA). It is found that HTA-AlN sputtered with pure nitrogen or mixed gases of nitrogen and trace oxygen exhibits undoubtable N polarity, which appears to contradict the common assumption of Al-polar AlN on Si-face SiC. The interfacial studies of HTA-AlN sputtered with pure N 2 reveal that the naturally oxidized SiC surface induces the formation of Si−O�Al−N bonds rather than conventional Si�N−Al bonds, thereby causing N-polar AlN. Sputtering with the mixed gases results in 5 nm thick complex transition layers at the AlN/SiC interface, including two types of oxygen-participated energy-unstable inversion domain boundaries and multiple polarity inverted AlN layers. Compared to that sputtered with the mixed gases, the N-polar HTA-AlN film sputtered with pure nitrogen presents a smoother surface morphology for the absence of AlON islands and lower threading dislocation density due to closer X-ray rocking curve full widths at half-maximum for (0002) and (101̅ 2) reflections. This work proves a new approach to prepare high-quality N-polar AlN/SiC templates for Al-rich AlGaN-based N-polar optoelectronic and power devices.

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N-polar III-nitride transistors

Cited by 14 publications

References 258 publications

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

Characterization of the N-polar GaN film grown on C-plane sapphire and misoriented C-plane sapphire substrates by MOCVD

Unexpected Realization of N-Polar AlN Films on Si-Face 4H–SiC Substrates Using RF Sputtering and High-Temperature Annealing

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