Articles you may be interested inUltraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts J. Appl. Phys. 116, 083108 (2014); 10.1063/1.4894251 Virtual GaN substrates via Sc 2 O 3 / Y 2 O 3 buffers on Si(111): Transmission electron microscopy characterization of growth defectsThe preparation of GaN virtual substrates on Si wafers via buffer layers is intensively pursued for high power/high frequency electronics as well as optoelectronics applications. Here, GaN is integrated on the Si platform by a novel engineered bilayer oxide buffer, namely, Sc 2 O 3 / Y 2 O 3 , which gradually reduces the lattice misfit of ϳ−17% between GaN and Si. Single crystalline GaN͑0001͒ / Sc 2 O 3 ͑111͒ / Y 2 O 3 ͑111͒ / Si͑111͒ heterostructures were prepared by molecular beam epitaxy and characterized ex situ by various techniques. Laboratory-based x-ray diffraction shows that the epitaxial Sc 2 O 3 grows fully relaxed on the Y 2 O 3 / Si͑111͒ support, creating a high quality template for subsequent GaN overgrowth. The high structural quality of the Sc 2 O 3 film is demonstrated by the fact that the concentration of extended planar defects in the preferred ͕111͖ slip planes is below the detection limit of synchrotron based diffuse x-ray scattering studies. Transmission electron microscopy ͑TEM͒ analysis reveal that the full relaxation of the Ϫ7% lattice misfit between the isomorphic oxides is achieved by a network of misfit dislocations at the Sc 2 O 3 / Y 2 O 3 interface. X-ray reflectivity and TEM prove that closed epitaxial GaN layers as thin as 30 nm can be grown on these templates. Finally, the GaN thin film quality is studied using a detailed Williamson-Hall analysis.
Ferrimagnetic spinel CoFe 2 O 4 (CFO) films are integrated with Si(111) using Sc 2 O 3 buffer layers. The huge lattice mismatch (17%) between CFO and Sc 2 O 3 is accommodated by domain matching, and CFO grows epitaxially with (111) out-of-plane orientation and coexistence of A-and B-type in-plane crystal variants. CFO films have low roughness of 4 Å and saturation magnetization of about 300 emu/cm 3 . These properties make CFO films on Sc 2 O 3 -buffered Si(111) comparable to those grown on oxide single crystals and thus extend the possibilities of using spinel oxides in electronic devices. 1,4 But the future incorporation of spinel oxides as active materials in electronics will critically depend on its epitaxial integration with silicon, which requires a buffer layer to avoid chemical interaction and allows lattice matching. Epitaxy of CFO and similar spinels has been achieved on Si(001), using yttria-stabilized zirconia (YSZ) as buffer layer.5,6 (111) faces in spinels typically have the lowest surface energy and thus these oxides tend to form (111) facetted islands when they grow (001)-oriented, 7 or to grow (111)-oriented, 5,6 which breaks the in-plane symmetry at the interface from four-to three-fold forming four in-plane CFO crystal variants. Si(111) wafers, favouring (111) out-of-plane orientation, can thus be a better choice as substrate for epitaxial growth of spinel films with higher crystalline quality.Some oxides that grow epitaxially and two-dimensionally directly on Si (111) 14 Sc 2 O 3 is a candidate as high-k dielectric for replacing conventional gate oxides in metal oxide semiconductor field effect transistors (MOSFETs). Its additional use as buffer layer for integration of ferrimagnetic CFO on silicon could add functionalities to complementary MOS (CMOS) logic circuits. However, the possibility of epitaxial growth of CFO (cubic Fd3m, a CFO ¼ 8.3919 Å ) on Sc 2 O 3 is challenging due to huge lattice mismatch:(a Sc2O3 À a CFO )/a CFO ¼ 17.3%. Nevertheless, domain matching epitaxy (DME) 15 could be active thus still leaving some room for high quality epitaxy. In DME, the misfit between film and substrate is reduced by matching of m lattice planes of the film with n lattice planes of the substrate. 15 There will be misfit dislocations in the domains, but each block of m lattice planes of the film accommodates on n lattice planes of the substrate with low overall strain.Using pulsed laser deposition (PLD), we have grown high quality epitaxial CFO films on Sc 2 O 3 /Si(111). It will be shown that CFO films are (111) out-of-plane oriented, they present two crystal variants (denoted A and B, corresponding to [11-2]
Thick (∼900 nm) GaN layers were grown by molecular beam epitaxy on cost-effective Sc2O3/Y2O3/Si(111) substrates and characterized by x-ray diffraction and photoluminescence. Samples grown in Ga-rich condition show superior structural and optical quality with reduced density of cubic GaN inclusions within the hexagonal matrix and a relatively strong photoluminescence emission at 3.45 eV at 10 K. Cubic inclusions are formed in the initial growth stage and their concentration is reduced with increasing film thickness and after rapid thermal annealing.
The defects and strain of GaN(0001) films as virtual substrate on Si(111) with step-graded Sc2O3(111)/Y2O3(111) buffers were investigated by means of transmission electron microscopy. The misfit dislocation network identified in the interfaces nearly fully compensates the lattice mismatch. Inversion domains and pinholes occur within the closed GaN film. The atomic structure of the inversion domain boundaries is identified. Major parts of the films were found to be N-polar. Threading dislocations were formed as remains from the coalescence of initial GaN islands. Furthermore, the formation of small cubic inclusions is found to be restricted to the vicinity of the interface only.
Articles you may be interested inUltraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts
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