AI 中文总结
研究（001）衬底上MOCVD生长的β-Ga2O3外延层开裂原因，通过系统研究发现其早期就采用特定取向结构，面内扭曲程度高于倾斜程度，因晶格失配产生拉伸应变致垂直方向裂纹形成，揭示外延关系与衬底表面重构有关。
AI 中文摘要
使用行业标准技术生长的厚且无缺陷的外延层是基于超宽带隙氧化镓（Ga2O3）的全垂直功率器件广泛应用的基本要求。然而，在最大直径（001）取向的天然β-Ga2O3衬底上进行此类层的金属有机化学气相沉积（MOCVD）仍相对未被充分探索，且随着厚度增加所报道的表面粗糙和开裂的起源尚未完全理解。为解决此问题，我们报告了对以约3.5μm/h的生长速率沉积、厚度从0.3到3.5μm的MOCVD生长的β-Ga2O3外延层的系统研究。外延层呈现相对光滑但有条纹的表面形态，从约1.8μm厚度起观察到合并和裂纹形成后纳米级粗糙度逐渐增加。高分辨率X射线衍射表明，尽管在（001）衬底上生长，但外延层从生长早期就主要采用（-401）取向结构。摇摆曲线分析进一步表明面内扭曲程度高于倾斜程度，两者都随外延层厚度增加而减小。虽然外延层和衬底在[010]面内方向晶格匹配，但在正交的外延层[104]面内方向的外延对准理论上会因底层晶格失配产生约+4.1%的最大面内拉伸应变，从而导致垂直于该方向的裂纹形成。我们的结果表明，这种外延关系可能与富氧MOCVD生长条件下表面能最小化驱动的（001）衬底表面刻面重构有关。
英文摘要
Thick, defect free epitaxial layers grown using industry standard techniques are a fundamental requirement for the widespread adoption of fully vertical power devices based on ultra wide bandgap gallium oxide (Ga2O3). However, metal-organic chemical vapour deposition (MOCVD) of such layers on native beta-Ga2O3 substrates with the largest diameter (001) orientation remains relatively unexplored, and the origins of the reported surface roughening and cracking with increasing thickness are not yet fully understood. To address this, we report a systematic study of MOCVD grown beta-Ga2O3 epilayers deposited at growth rates of ~3.5 um/h, with thicknesses from 0.3 to 3.5 um. The epilayers exhibit a relatively smooth but striated surface morphology, with progressively increasing nanometre-scale roughness beyond coalescence and crack formation observed from ~1.8 um thickness. High resolution X ray diffraction reveals that, despite growth on (001) substrates, the epilayers adopt a predominantly (-401)-oriented structure from the earliest stages of growth. Rocking curve analysis further indicates a higher degree of in-plane twist than tilt, both decreasing with increasing epilayer thickness. While the epilayer and substrate are lattice-matched along the [010] in plane direction, the epitaxial alignment in the orthogonal epilayer [104] in plane direction imposes, in theory, a maximum tensile in-plane strain of approximately +4.1% arising from the underlying lattice mismatch, thereby driving crack formation perpendicular to this direction. Our results suggest that this epitaxial relationship is likely associated with faceted reconstruction of the (001) substrate surface during annealing, driven by the minimisation of surface energy under oxygen-rich MOCVD growth conditions.
CommentsMain article: 16 pages with 7 figures
