Novel materials with unique electronic properties are required to meet the demands of next-generation electronic systems. This dissertation discusses the use of novel materials, such as the perovskite oxides barium titanate (BaTiO3) and barium stannate (BaSnO3), and the three-dimensional Dirac semimetal cadmium arsenide (Cd3As2), for field-effect devices with distinctive transistor characteristics.
Integration of ultrathin epitaxial ferroelectric thin films on semiconductor channels is of great interest for novel low power switching and memory applications. The first section of this dissertation covers BaTiO3/SrTiO3, a ferroelectric-semiconductor heterostructure. The electronic properties of this heterostructure confirm that the BaTiO3 thin film is ferroelectric. An anti-clockwise hysteresis is observed in BaTiO3/SrTiO3-based capacitors and the characteristics of field-effect transistors are also consistent with the ferroelectric nature of the BaTiO3 thin films. Furthermore, the BaTiO3 thin films are under biaxial compressive stress, which enhances the ferroelectricity and increases the Curie temperature. This section also discusses the epitaxial growth of a high mobility perovskite oxide, BaSnO3, and reports the highest mobility in BaSnO3 thin film – 215 cm2/Vs.
The second part of this dissertation covers Cd3As2, a three-dimensional Dirac semimetal with topologically non-trivial electronic states. Quantum capacitance measurements exhibit zero-energy Landau level, confirming Dirac surface states on the Cd3As2 thin films. Due to topologically nontrivial energy states, Cd3As2 thin films display interesting magnetotransport characteristics. Berry phase effects lead to a negative transverse magnetoresistance in Cd3As2 thin films. The effect of the Berry phase can be tuned by altering film thicknesses or shifting Fermi level. Moreover, Cd3As2 based field effect transistors have the potential to operate in the THz regime, owing to the high Fermi velocity. Additionally, theoretical analysis shows linearity in transistor performance. This study demonstrates the first field-effect transistor with a Cd3As2 channel. Cd3As2 devices exhibit extraordinarily high current densities (10 A/mm) and ultra-low contact resistance (<2 × 10−9 Ωcm2). Improvements in the fabrication process and transistor structure enhance the current modulation (> 50%) and transconductances (120 mS/mm) of a Cd3As2 field-effect transistor. There is a potential for a 10× improvement in transconductance by reducing trap densities. Preliminary results demonstrate the vast potential of Cd3As2 field-effect transistors for high-speed THz electronics.