Strain Release in GaN Epitaxy on 4° Off‐Axis 4H‐SiC

Abstract

A hybrid field‐effect transistor (HyFET), superior for power electronic applications, can be created by harnessing the merits of two representative wide‐bandgap semiconductors, gallium nitride (GaN) and silicon carbide (SiC). Yet, the incompactness in the epitaxy techniques hinders the development of the HyFET—GaN is usually grown on on‐axis foreign substrates including SiC, whereas SiC homoepitaxy prefers off‐axis substrates. This work presents a GaN‐based heterostructure epitaxially grown on a conventional 4° off‐axis 4H‐SiC substrate, which manifests its high quality and suitability for constructing GaN‐based high‐electron‐mobility transistors, thereby suggesting a practical approach to realizing HyFETs. In the meanwhile, a distinct two‐step biaxial strain‐relaxation process is proposed and studied with comprehensive characterizations.

Optical, Structural, and Synchrotron X-ray Absorption Studies for GaN Thin Films Grown on Si by Molecular Beam Epitaxy

“…The GaN E 2 (high) phonon mode can be used to measure the stress [ 18 , 37 , 38 ]. The GaN with free strain possesses an E 2 (high) phonon frequency of 567.5 cm −1 [ 18 ].…”

“…The GaN with free strain possesses an E 2 (high) phonon frequency of 567.5 cm −1 [ 18 ]. The Raman frequency difference of the GaN E 2 mode relative to the strain-free one Δω was used to calculate the layer stress using the formula: σ = Δω/K, where K = −4.3 cm −1 GPa −1 is the conversion factor of GaN Raman biaxial stress [ 37 , 38 ]. From the Lorentzian fitted E 2 mode peak values listed in Table 4 , S3 (NS38) and S6 (NS41) were found to exhibit tensile stress, while S2 (NS37) and S7 (NS48) were found to exhibit compressive stress.…”

“…The GaN E2(high) phonon modes were very clearly displayed, unlike Figure 4, mixed with the Si 520 cm −1 mode. The GaN E2(high) phonon mode can be used to measure the stress [18,37,38]. The GaN with free strain possesses an E2(high) phonon frequency of 567.5 cm −1 [18].…”

“…The Raman frequency difference of the GaN E2 mode relative to the strain-free one Δω was used to calculate the layer stress using the formula: σ = Δω/K, where K = −4. The GaN E 2 (high) phonon mode can be used to measure the stress [18,37,38]. The GaN with free strain possesses an E 2 (high) phonon frequency of 567.5 cm −1 [18].…”

Epitaxially ferroelectric hexagonal boron nitride on graphene

“…In contrast to CVD, which depends on the catalytic effect of the substrate, molecular beam epitaxy (MBE) is conventionally well suited to the massive growth of multilayer stacked structures as it offers high-precision control of a source flux as well as in situ reflection high-energy electron diffraction (RHEED) characterization. Here, we apply nitrogen plasma-assisted MBE (PA-MBE) for the direct growth of layer-controlled h-BN on the crystalline matched graphene prepared on a 4H-SiC (0001) substrate with a miscut angle of 4°, which is available on the market mainly for the epitaxy of highquality III-nitrides with an enhanced growth rate 24 . After careful annealing under an ultra-high vacuum (UHV) environment, the homogeneously multilayered graphene can be epitaxially grown on the SiC substrate with surface steps following the <112 ̅ 0> direction (Figs.…”