Yılmaz S. N., Doğan U., Aydoğdu M., Aydın M., Yakut Ş., Bozoğlu Parto D., ...Daha Fazla
NANOTR-20, İzmir, Türkiye, 26 - 28 Ağustos 2026, ss.1, (Özet Bildiri)
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Yayın Türü:
Bildiri / Özet Bildiri
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Basıldığı Şehir:
İzmir
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Basıldığı Ülke:
Türkiye
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Sayfa Sayıları:
ss.1
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İstanbul Üniversitesi Adresli:
Evet
Özet
Gallium oxide (β-Ga₂O₃) has emerged
as a premier ultra-wide-bandgap semiconductor for next-generation high-power
electronics and deep-ultraviolet optoelectronics because of its high breakdown
field and scalable bulk growth. Due to its low monoclinic symmetry, the
macroscopic properties of β-Ga₂O₃ are highly anisotropic, making
orientation-aware substrate selection and process monitoring critical for
advanced device engineering. This study systematically investigates the
orientation-dependent structural and optical evolution of unintentionally doped
(UID) and tin (Sn)-doped bulk β-Ga₂O₃ single crystals grown by the edge-defined
film-fed growth (EFG) method. To resolve the coupled effects of structural
anisotropy and heavy donor incorporation, 2-inch wafers with (001) and (2̄01)
surface orientations were comprehensively evaluated across a wide range of
donor concentrations using angle-resolved high-resolution X-ray diffraction
(HRXRD) and room-temperature optical absorption spectroscopy.
Angle-resolved HRXRD measurements
confirm that all samples maintain a phase-pure monoclinic structure (space
group C2/m) with no detectable secondary phases, such as SnO or SnO₂, at any
azimuthal rotation angle. This demonstrates that both orientations successfully
accommodate heavy n-type doping without phase degradation. However, structural
quality shows a strong orientation dependence, indicating that the structural
perfection of these substrates is fundamentally governed by their
crystallographic plane. The (001)-oriented wafers display significantly
narrower full-width at half-maximum (FWHM) values than the (2̄01) counterparts,
indicating superior crystalline perfection and a minimized mosaic spread along
the c-axis. Furthermore, Sn incorporation in the (001) series modestly narrows
the FWHM values, suggesting that donor doping may mitigate native point defects
or relax local strains during EFG melt growth while preserving the superior
structural framework of the (001) plane.
Optical absorption
analysis shows that both the crystallographic orientation and Sn-doping
profiles strongly govern the fundamental band-edge response and the near-edge
optical landscape. Under unpolarized conditions, the Tauc-derived effective
optical bandgap of the UID samples is resolved at 4.65 eV for the (001)
orientation and 4.63 eV for the (2̄01) orientation, directly reflecting the
intrinsic optical anisotropy of the monoclinic lattice. With increasing Sn
incorporation, both orientation series exhibit a significant,
concentration-dependent blue shift of the absorption edge by up to 53 meV,
demonstrating that the effective bandgap can be controllably expanded via the
Burstein-Moss shift. This substantial blue shift is consistent with the filling
of the lowest conduction-band states as the Fermi level moves upward.
Logarithmic absorption-tail (ln(α)-E) analyses reveal distinct sub-bandgap
disorder characteristics between the two orientations; the (2̄01) series shows
a robust baseline, with the broad near-edge tail of the undoped crystal notably
narrowing and stabilizing upon Sn introduction.
Keywords: β-Ga₂O₃, Single crystal, HRXRD, Structural anisotropy, Optical
absorption, Burstein-Moss shift.