Integration of functional oxides with the semiconductor zinc oxide

Ferroelectric/semiconductor heterostructures are desirable for multifunctional devices using the charge of a ferroelectric material to manipulate the conductivity of a semiconductor. The quality of the ferroelectric/semiconductor interface is critical for maintaining a significant ferroelectric polarization charge density, and coupling this charge density into the semiconductor. Therefore, materials must have 'excellent chemical and structural compatibility. The semiconductor ZnO is a promising candidate for integration with ferroelectric oxides, due to its excellent structural and chemical compatibility with such materials.This report discusses the thin film growth of select ferroelectric and semiconductor materials, the fabrication of heterostructures and basic capacitor devices using such materials, and the characterization of structural and electrical properties thereof. Pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) are used to obtain thin films of desired materials. Standard lithographic methods were used to pattern the materials and to deposit electrical contacts for subsequent testing.Polycrystalline thin films of Pb(Zr,Ti)O3 (PZT) were achieved through solution processing, and they exhibited ferroelectric behavior in polarization-electric field and capacitance-voltage measurements. Single crystal substrates of ferroelectric LiNbO3 (LN) were purchased in bulk form. Weak c-plane preferential orientation of ZnO thin films was achieved using PLD on PZT filins. Highly preferentially oriented c-plane ZnO films were obtained by PLD on LN substrates.Ferroelectric/Zno heterostructures using PZT and LN as prototype ferroelectric materials were studied. Pt/PZT/ZnO capacitors showed a memory window of 2V in capacitance-voltage and AC conductance measurements. An RLC circuit constructed using the PZT/ZnO capacitor shows a resonant peak shift of 30kHz, which is consistent with the expected change in capacitance with switching ferroelectric polarization. LiNbO3/ZnO heterostructures show evidence of carrier concentration modulation in the semiconductor attributed to the ferroelectric polarization charge. Hall effect measurements revealed an order of magnitude reduction in measured carrier concentration in the ZnO thin film consistent with expected depletion caused by the ferroelectric polarization charge. The pyroelectric effect in LN substrates was exploited using a basic voltage divider circuit where the change in ZnO conductivity could be observed. Upon application of heat, the ferroelectric polarization charge increased, thereby causing further depletion of the ZnO film.