Epitaxial Integration Of Functional Oxides On Silicon (100)

Abstract

Epitaxial integration of BaTiO3 (BTO) and other functional oxides with (100) Si is essential to exploit their functional capabilities using the well-established Si-CMOS technological platform. However, such oxide integration is impeded by the presence of native amorphous SiOx on Si surfaces and its formation during oxide deposition. Buffer layers of oxides that are thermodynamically more stable than SiOx are often introduced in order to mitigate the same. Heterogenous integration either employs an expensive molecular beam epitaxy process (STO layer) or a complex transition scheme (BTO/LNO/CeO2/YSZ/Si). While BaTiO3 – a ferro electric of importance for various electronic and photonic applications- is the main oxide considered herein, similar approaches have also helped integrate Ga2O3 – an emerging oxide of importance to power electronic and UV applications-as described towards the end of the thesis. Epitaxial growth of a CMOS compatible buffer layer titanium nitride (TiN) via reactive PLD (RPLD) is demonstrated in chapter 2. By implementing geometric modifications (eclipsed off-axis), TiN films with record low particulate density ~ 6x103 cm-2 and at high growth rates of ~1μm/hr are obtained. In chapter 3, the feasibility of BaTiO3 integration on Si (100) using this single TiN transition layer is explored. The polarization (c-axis) axis in BaTiO3 and its relative orientation w.r.t substrate normal dictates its application as a memory device (out of plane BTO) or an electro-optic (in-plane BTO) modulator. In the literature lattice-matched substrates are employed to achieve the same. However, this is not possible on Si, as the substrate Si is fixed. Epitaxial BaTiO3 films with both c-axis in-plane and out-of-plane polarization are demonstrated on TiN/Si(100). This change in polarization direction is brought about very simply by changing the growth temperature. Though good quality c-OP BaTiO3 films grown via TiN/Si are suited for memory applications, integrated electro-optic (E-O) applications based on c-IP BaTiO3 require an insulating buffer to limit the light propagation losses. In chapter 4, the feasibility of epitaxial growth of in-plane BaTiO3 via insulating the MgO layer on Si (100) using PLD is explored. The epitaxial in-plane BaTiO3 films on MgO/Si are electro-optically active and have the potential to be used in on-chip E-O modulators. In the last chapter of this thesis, heterogeneous integration of a binary wide bandgap semiconductor β-Ga2O3 (4.8 eV) on Si (100) platform is investigated to enable compact focal plane sensor arrays in deep ultraviolet regime on a CMOS chip. For the first-time epitaxial integration of β-Ga2O3 on (400) oriented silicon on insulator (SOI) (100) substrate has been reported.