Determination of Hafnium Zirconium Oxide Interfacial Band Alignments Using Internal Photoemission Spectroscopy and X-ray Photoelectron Spectroscopy.

Doped ferroelectric HfO2 is highly promising for integration into complementary metal-oxide semiconductor (CMOS) technology for devices such as ferroelectric nonvolatile memory and low-power field-effect transistors (FETs). We report the direct measurement of the energy barriers between various metal electrodes (Pt, Au, Ta, TaN, Ti/Pt, Ni, Al) and hafnium zirconium oxide (Hf0.58Zr0.42O2, HZO) using internal photoemission (IPE) spectroscopy. Results are compared with valence band offsets determined using the three-sample X-ray photoelectron spectroscopy (XPS) as well as the two-sample hard X-ray photoelectron spectroscopy (HAXPES) techniques. Both XPS and IPE indicate roughly the same dependence of the HZO barrier on metal work function with a slope of 0.8 ± 0.5. XPS and HAXPES-derived barrier heights are on average about 1.1 eV smaller than barrier heights determined by IPE, suggesting the presence of negative charge in the HZO.

Demonstration of Fowler-Nordheim Tunneling in Simple Solution-Processed Thin Films.

The production of high-quality thin-film insulators is essential to develop advanced technologies based on electron tunneling. Current insulator deposition methods, however, suffer from a variety of limitations, including constrained substrate sizes, limited materials options, and complexity of patterning. Here, we report the deposition of large-area Al2O3 films by a solution process and its integration in metal-insulator-metal devices that exhibit I- V signatures of Fowler-Nordheim electron tunneling. A unique, high-purity precursor based on an aqueous solution of the nanocluster flat-Al13 transforms to thin Al2O3 insulators free of the electron traps and emission states that commonly inhibit tunneling in other films. Tunneling is further confirmed by the temperature independence of device current.

Enhanced NMR with Optical Pumping Yields 75As Signals Selectively from a Buried GaAs Interface.

We have measured the 75As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.