Abstract
We experimentally demonstrate how In-mediated metal-exchange catalysis (MEXCAT) allows us to widen the deposition window for β-Ga2O3 homoepitaxy to conditions otherwise prohibitive for its growth via molecular beam epitaxy (e.g., substrate temperatures ≥800 °C) on the major substrate orientations, i.e., (010), (001), (2¯01), and (100) 6°-offcut. The obtained crystalline qualities, surface roughnesses, growth rates, and In-incorporation profiles are shown and compared with different experimental techniques. The growth rates, Γ, for fixed growth conditions are monotonously increasing with the surface free energy of the different orientations with the following order: Γ(010) > Γ(001) > Γ(2¯01) > Γ(100). Ga2O3 surfaces with higher surface free energy provide stronger bonds to the surface ad-atoms or ad-molecules, resulting in decreasing desorption, i.e., a higher incorporation/growth rate. The structural quality in the case of (2¯01), however, is compromised by twin domains due to the crystallography of this orientation. Notably, our study highlights β-Ga2O3 layers with high structural quality grown by MEXCAT-MBE not only in the most investigated (010) orientation but also in the (100) and (001) ones. In particular, MEXCAT on the (001) orientation results in both growth rate and structural quality comparable to the ones achievable with (010), and the limited incorporation of In associated with the MEXCAT deposition process does not change the insulating characteristics of unintentionally doped layers. The (001) surface is therefore suggested as a valuable alternative orientation for devices.
Highlights
For these reasons, the homoepitaxy of β-Ga2O3 by molecular beam epitaxy (MBE) has so far been mostly restricted to the (010) orientation and growth conditions that are not limiting its growth rate (e.g., O-rich, Tg < 800 ○C).10,16 In contrast, metal-rich deposition conditions are predicted to avoid the formation of gallium vacancies18,19 and higher Tg generally result in higher crystalline quality and allows us to increase the stability range of β-(AlxGa1−x)2O3 alloys.20 substrate orientations other than (010) are desirable to mitigate the following drawbacks: (i) the (010) surface has been shown to be unstable under metal-rich growth conditions, i.e., resulting in the formation of (110)-facets,21 and (ii) it is not a cleavage plane and currently more challenging to be prepared22 with respect to the (001), (2 ̄01), and (100)
We experimentally demonstrate how In-mediated metal-exchange catalysis (MEXCAT) allows us to widen the deposition window for βGa2O3 homoepitaxy to conditions otherwise prohibitive for its growth via molecular beam epitaxy on the major substrate orientations, i.e., (010), (001), (2 ̄01), and (100) 6○-offcut
Sn-flux mediated Ga2O3 heteroepitaxy by MEXCAT-MBE24 lead to the same qualitative results, demonstrating the generality of the MEXCAT approach for MBE. Both Sn- and In-mediated MEXCAT-MBE performed on top of a buffer layer of (2 ̄01)-oriented β-Ga2O3 on c-plane sapphire substrates resulted in the formation of the metastable ε/k-phase of
Summary
ARTICLES YOU MAY BE INTERESTED IN A review of Ga2O3 materials, processing, and devices Applied Physics Reviews 5, 011301 (2018); https://doi.org/10.1063/1.5006941 Recent progress on the electronic structure, defect, and doping properties of Ga2O3 APL Materials 8, 020906 (2020); https://doi.org/10.1063/1.5142999 Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal Ga2O3 (010) substrates Applied Physics Letters 100, 013504 (2012); https://doi.org/10.1063/1.3674287
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