Direct growth of GaN film on ScAlMgO 4 substrate by radio-frequency plasma-excited molecular beam epitaxy

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ScAlMgO4 (SAM) substrates have attracted considerable attention as platforms for GaN growth in recent years because GaN can be grown directly on SAM without any buffer layer. Herein, the effect of the terrace width of SAM substrates on direct GaN growth is investigated using radio‐frequency molecular beam epitaxy (RF‐MBE). A flat and single wurtzite (WZ)‐phase GaN film is grown on a SAM substrate with a large terrace width. In contrast, a rough GaN film with a mixture of WZ and zinc‐blende (ZB) phases is obtained on SAM with a small terrace width. The SAM step height of 0.8 nm corresponds to three GaN molecular layers. Therefore, ZB stacking faults may be generated during the coalescence of islands located on adjacent terraces, although only the WZ‐GaN islands grow in the initial growth stage. This indicates that SAM substrates with a larger terrace width, that is, a smaller off‐cut angle, are preferable for obtaining a flat WZ‐GaN film.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Substrate Terrace Width Dependence of Direct Growth of GaN on ScAlMgO₄ by Radio‐Frequency Molecular Beam Epitaxy

Wada

Deura

Kuroda

et al. 2023

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Direct Growth of Nearly Lattice‐Matched InGaN on ScAlMgO₄ Substrates Using Radio‐Frequency Plasma‐Assisted Molecular Beam Epitaxy

Kubo,

Deura,

Yamada

et al. 2024

ScAlMgO4 (SAM) has attracted considerable attention as a substrate for growing InGaN template layers owing to its lattice matching with In0.17Ga0.83N. Furthermore, radio‐frequency plasma‐assisted molecular beam epitaxy (RF‐MBE) can be utilized to grow (In)GaN directly on SAM substrates because the growth is conducted at relatively low temperatures without reactive gases. This prevents the diffusion and desorption of the constituent elements of the SAM substrate. In this study, the substrate‐temperature dependence of the direct growth of InGaN on SAM substrates is investigated through RF‐MBE. In droplets are formed below 600 °C, whereas, the In content of the InGaN crystal decreases rapidly, and the surface roughness increases at ≈650 °C. These results are attributed to the acceleration of In desorption at higher temperatures. The improvement in crystal coherency moderates above 600 °C. Therefore, a nearly lattice‐matched In0.18Ga0.82N film is grown at an optimal temperature of 600 °C by adjusting the group‐III metal fluxes. The resulting film is continuous and relatively flat, with no droplets. The dislocation density with screw component is one order of magnitude lower than that of the lattice‐mismatched InGaN. The dislocation density of the InGaN film is comparable to that of a film grown by metal‐organic vapor‐phase epitaxy.

Investigation of Nondestructive and Noncontact Electrical Characterization of GaN Thin Film on ScAlMgO₄ Substrate Using Terahertz Time‐Domain Spectroscopic Ellipsometry with Characteristic Impedance Analytical Model

Watanabe,

Wang,

Fujii

et al. 2024

Semiconductor evaluation methods frequently require sample processing and carry the risk of defects and property changes. Therefore, nondestructive and noncontact electrical property measurement techniques are necessary. Terahertz time‐domain spectroscopic ellipsometry (THz‐TDSE) can simultaneously estimate the electrical properties and film thickness of a sample. However, whether this method can simultaneously determine electrical properties and film thickness for semiconductor thin films of 1 μm or less remains unclear. This study uses THz‐TDSE to evaluate the electrical properties and film thickness of a GaN thin film (≈0.8 μm thick) on a ScAlMgO4 substrate. Using the conventional analysis based on Fresnel's formula (FR model), which is used in the field of optics, uniquely determining the electrical properties and film thickness is not possible owing to multiple optimal solutions. Therefore, a model combining the characteristic impedance model used in the radio‐wave region with the FR model is employed in the analysis. The obtained values of electrical properties of the GaN thin film evaluated using THz‐TDSE are consistent with those using Hall effect measurement. Moreover, the film thickness is consistent with that measured from the cross‐sectional transmission electron microscopy observation.