Bandgap engineering of α-(AlxGa1-x)2O3 by a mist chemical vapor deposition two-chamber system and verification of Vegard's Law

Abstract

This work reports growth of α-(AlxGa1-x)2O3 single crystals with high incorporation of Al by a Mist Chemical Vapor Deposition two-chamber system, which was rationally designed to avoid side-reactions between different precursors during solution preparation for multi-component thin film growth. Multiple acceleration voltages were used in Energy Dispersive X-ray measurements to reliably obtain the Al composition x of the films. As a result, Vegard's law for lattice constants was verified and found to be valid in the α-(AlxGa1-x)2O3 system. However, Vegard's law for optical bandgaps, derived from different models, required an additional term to account for the bowing effect. At x = 0.71, the gaps were 7.74, 7.03, 7.26, and 7.34 eV as derived from the Tauc plots for the direct bandgap, indirect bandgap, Tauc-Lorentz model, and O'Leary-Johnson-Lim model, respectively. The two-chamber system provides reliable and effective control of the Al content in α-(AlxGa1-x)2O3 alloys and heterostructures.

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

“…The constants derived for the α‐ thin films coincides for with literature values [ 25,28 ] and follow Vegard's law. The transition to pseudomorphic growth at around is influenced by the thin‐film thickness (here 240 nm) and will occur at higher Al concentrations for thicker thin films.…”

“…In contrast to this current study, Ito et al, Dang et al, and Fujita et al reported growth of relaxed α‐ thin films in the entire composition range, pseudomorphic growth was not. [ 25,28,38 ] Grundmann et al reported a similar transition composition for thin films in r‐plane sapphire, which might be due to different relaxation mechanisms, e.g., for (01.2)‐oriented thin films relaxation may occur via prismatic glide planes which is not possible for the (11.0)‐oriented thin films discussed here.…”

“…Successful fabrication of rhombohedral Ga 2 O 3 was reported by mist chemical vapor deposition (CVD), [ 13,17,19,21–23 ] halide vapor phase epitaxy (HVPE), [ 14,16,24 ] metalorganic vapor phase epitaxy (MOVPE), [ 15 ] mist epitaxy, [ 19 ] and the sol–gel method, [ 12 ] whereas ternary α‐ has been realized by mist CVD, [ 25–28 ] PLD, [ 29,30 ] and molecular beam epitaxy (MBE) [ 31 ] until now. As substrates, a ‐, c ‐, m ‐, or r ‐plane sapphire are possible to use.…”

Probing structural and chemical evolution in (AlxGa1−x)2O3 using atom probe tomography: A review

“…(Al x Ga 1−x ) 2 O 3 has shown unique properties including enhanced predicted breakdown strength with an improved chemical and thermal stability [10,11], making it highly desirable for high power electronics and deep ultraviolet optical applications [9,12]. The bandgap in (Al x Ga 1−x ) 2 O 3 tends to increase monotonically with the incorporation of Al content [12,13] that forms (Al x Ga 1−x ) 2 O 3-/Ga 2 O 3 heterostructures with large band offset [9]. This elevated bandgap has enabled successful realization of (Al x Ga 1 −x ) 2 O 3 based field-effect transistors [11,14,15,16], Schottky barrier diodes [17,18], and photodetectors [19,20,21].…”

Probing structural and chemical evolution in (AlxGa1−x)2O3using atom probe tomography: A review

“…Due to the similar electronic structure of Ga and Al with Al 2 O 3 exhibiting a higher bandgap [9], it was possible to widen the bandgap of shown unique properties including enhanced predicted breakdown strength with an improved chemical and thermal stability [10,11], making it highly desirable for high power electronics and deep ultraviolet optical applications [9,12]. The bandgap in (Al x Ga 1−x ) 2 O 3 tends to increase monotonically with the incorporation of Al content [12,13] that forms (Al x Ga 1−x ) 2 O 3-/Ga 2 O 3 heterostructures with large band offset [9]. This elevated bandgap has enabled successful realization of (Al x Ga 1 −x ) 2 O 3 based field-effect transistors [11,14,15,16], Schottky barrier diodes [17,18], and photodetectors [19,20,21].…”