The electrical characteristics of ZnO thin-film transistors with high-k ͑Ba, Sr͒TiO 3 gate dielectrics are presented. The ZnO and ͑Ba, Sr͒TiO 3 thin films were deposited on Pt, exhibiting polycrystalline characteristics. The thin-film devices demonstrated transistor behavior over the range of 0-10 V with a stable threshold voltage of approximately 1.2 V. The field effect mobility, subthreshold slope, and on/off ratio were measured to be 2.3 cm 2 V −1 s −1 , 0.25 V / decade, and 1.5ϫ 10 8 , respectively. The measured transistor performance characteristics suggest that ZnO / ͑Ba, Sr͒TiO 3 structures are well suited for both polycrystalline thin-film transistors for display applications and future higher performance transistors based on single crystal ZnO.

Interfacing of ferroelectric and semiconductor materials provides a means of coupling unique properties associated with ferroelectric materials to high performance semiconductor devices. In this work we report the electronic properties of ferroelectric/ZnO heterostructures, where (Pb,Zr)TiO 3 (PZT) is used as a prototypical ferroelectric oxide. Metal-PZT-metal structures demonstrate ferroelectric hysteresis with remanent polarization of 28 µC cm −2 and coercive field of 75 kV cm −1 for a loop of 15 V. The metal-PZT-ZnO capacitor structures demonstrate a characteristic metal-insulator-semiconductor capacitance-voltage (C-V) behaviour with a hysteretic memory window of approximately 4 V. The heterostructure C-V characteristics do not change significantly with varying frequency. Metal-PZT-ZnO capacitors are also used as part of a simple RLC circuit to demonstrate the ability to shift resonant frequency of the circuit with switching ferroelectric polarization.

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Significant wafer curvature has been observed for AlGaN/GaN high electron mobility transistor (HEMT) structures grown on SiC substrates by rf plasma molecular-beam epitaxy. The curvature is caused by residual compressive strain in the films, due primarily to the lattice mismatch between substrate and epilayer. The wafers exhibit more bow when an AlN nucleation layer is used, than when GaN/AlGaN is grown directly on SiC. However, in test structures, AlN nucleation layers are found to impart tensile strain in the wafer that is small due to the AlN thickness. Using high resolution x-ray diffraction with reciprocal space maps, thin GaN films are found to relax more readily when grown directly on SiC substrates than on AlN buffer layers. The compressive strain in the thick GaN buffer layer grown on AlN bows the wafer and increases the substrate x-ray diffraction (XRD) linewidth. The GaN buffer, despite its thickness, does not relax fully but retains some residual strain.