Atomic layer deposition of epitaxial perovskites for electronic and photonic applications

This research focuses on growth of ferroelectric and conductive perovskite oxides for both electronic and photonic applications. The advancement of computing technologies requires new device architectures, new materials, and new processing techniques. Perovskite class oxides, which have the general formula of ABO₃, possess various types of properties. The ability to grow perovskite oxides epitaxially on Si and Ge(001) single crystals provides an opportunity for incorporating various properties of perovskite onto semiconductor devices. In particular, barium titanate (BaTiO₃, BTO) is ferroelectric enabling opportunities in reducing transistor power consumption and fabricating photonic devices. The advancement in growing epitaxial perovskite oxides on Si(001) with a strontium titanate (SrTiO₃, STO) buffer layer via atomic layer deposition (ALD) shows the promise of using ALD to integrate perovskite properties into semiconductor materials. In order to realize the benefit brought by BTO, BTO films deposited by ALD need to exhibit ferroelectric polarization. This work initially focuses on ALD growth of BTO on Ge(001) and STO-buffered Si(001) single crystal substrates. Ferroelectric polarization was observed on the BTO films deposited on STO-buffered Si(001) substrates. The c-axis direction, which is the direction of BTO ferroelectric polarization, of BTO films with thickness up to 66 nm can be controlled by adjusting post-deposition annealing parameters. Ferroelectric switching of BTO on STO-buffered Si(001) in out- of-plane and in-plane directions were demonstrated by piezoresponse force microscopy and electro-optic measurement, respectively. Another part of this work concerns the mismatch between the range of BTO polarization and the polarization range needed to switch Si transistor channels. One proposal to address the mismatch is to introduce a thin conductive layer to attenuate BTO polarization. An MBE-ALD approach was developed to grow the conductive La:STO layer between a ferroelectric BTO film and the Si(001) substrate. Capacitance-voltage measurements of the BTO/La:STO film grown on STO-buffered Si(001) demonstrate attenuation of an externally applied electric field by La:STO, which is a result of the La:STO film conductivity. Lastly, this work explores the possibility of selective growth of BTO. Pattern transfer of the ALD grown film was observed by atomic force microscopy. The patterned film crystallizes after annealing the film in vacuum to the temperature of 800 °C.Chemical Engineerin