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- ItemEvolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model(Melville, NY : American Inst. of Physics, 2016) Schewski, R.; Baldini, M.; Irmscher, K.; Fiedler, A.; Markurt, T.; Neuschulz, B.; Remmele, T.; Schulz, T.; Wagner, G.; Galazka, Z.; Albrecht, M.We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10−9 cm2 s−1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.
- ItemSubstrate-orientation dependence of β -Ga2O3 (100), (010), (001), and (2 ̄ 01) homoepitaxy by indium-mediated metal-exchange catalyzed molecular beam epitaxy (MEXCAT-MBE)(Melville, NY : AIP Publ., 2020) Mazzolini, P.; Falkenstein, A.; Wouters, C.; Schewski, R.; Markurt, T.; Galazka, Z.; Martin, M.; Albrecht, M.; Bierwagen, O.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.
- ItemInterface polarization model for a 2-dimensional electron gas at the BaSnO3/LaInO3 interface([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Kim, Young Mo; Markurt, T.; Kim, Youjung; Zupancic, M.; Shin, Juyeon; Albrecht, M.; Char, KookrinIn order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface.