Silane‐Mediated Expansion of Domains in Si‐Doped κ‐Ga₂O₃ Epitaxy and its Impact on the In‐Plane Electronic Conduction

Abstract

Unintentionally doped (001)-oriented orthorhombic κ-Ga 2 O 3 epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in-and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm 2 V −1 s −1 , with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga 2 O 3 epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga 2 O 3 and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties.

Orthorhombic undoped κ-Ga2O3 epitaxial thin films for sensitive, fast, and stable direct X-ray detectors

“…It is worth noting here that often the literature indifferently reports κ-and ε-Ga 2 O 3 ; this ambiguity originates from the six-fold symmetry of early diffraction patterns and the consequent classification of such Ga 2 O 3 phase as "hexagonal", hence the ε-Ga 2 O 3 ascription. A comprehensive TEM study 20 , as well as other works recently published [21][22][23][24] , showed definitely that the so-called κ phase is indeed orthorhombic and not hexagonal. In analogy to the usual nomenclature of other metal-oxides, it is therefore correct to denominate the orthorhombic phase as κ, as it will be done in this paper.…”

Interfacial Properties of the SnO/κ-Ga2O3 p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-Ga2O3

“…Among the possible phenomena leading to the observed alteration of the doping profile, the thermally activated out-diffusion of hydrogen is certainly a plausible hypothesis; in fact, interstitial hydrogen is expected to be a shallow donor in κ-Ga 2 O 3 , as already predicted for β-Ga 2 O 3 . Hydrogen can derive from the precursors and the carrier gas in κ-Ga 2 O 3 layers. , In κ-Ga 2 O 3 layers grown using H 2 carrier gas but without providing an additional silane (SiH 4 ) flow, resistivity of about 10 5 Ω·cm was typically obtained. , This implies that only a minor fraction of molecular hydrogen gas acts as a shallow donor, but we cannot exclude that a much more effective hydrogen incorporation may take place when the silane gas cracks at the surface of the growing κ-Ga 2 O 3 layers, with release of atomic H. Therefore, it is plausible that both atomic hydrogen and silicon can contribute to establish the n-type conductivity.…”

“…It is worth noting that we also analyzed the effect of different mobility values in-plane and perpendicular to the junction. Such anisotropy in the mobility values originates from the formation of columnar domains in the κ-Ga 2 O 3 . It can be noted that the dominant transport mechanism for in-plane conduction is the variable range hopping, leading to low mobility values .…”

“…In the following, we shall use the name κ, more appropriate for identification of the microscopic structure of this phase. The domain walls, together with other vertically oriented planar defects, have been demonstrated to play a detrimental role for the in-plane electronic conduction of κ-Ga 2 O 3 thin films resulting in a defect mediated conduction anisotropy (at least 1 order of magnitude lower resistivity in out-of-plane electrical measurements with respect to in-plane ones) . Therefore, domain elimination (e.g., through epitaxially matched GaFeO 3 substrates) is an important issue for the further development of this polymorph.…”

Photoelectron Holographic Study for Atomic Site Occupancy for Si Dopants in Si-Doped κ-Ga2O3(001)

“…The defects are mostly perfectly vertically oriented, i.e., 3 × 120°rotated domains and antiphase boundaries. 7,23,24 In addition, these vertically oriented structural defects could be electrically charged. 24 On the other hand, the first-principles calculations of Zeman et al do not contain the charged structural defects, vertically oriented and rotated domains, and antiphase boundaries.…”