This study examines the atomic force microscope (AFM) tip-based electrical formation of tens of microns long stripe (and B100 nm wide) inorganic one-dimensional nanostructures based on the morphotropic phase boundary of La-doped BiFeO 3 epitaxial thin films. The substitution of Lanthanum into bismuth ferrite not only produces the formation of straight stripe mixedphase patterns but also improves the spatial continuity drastically by two orders of magnitude. We create, switch and erase stripe nanostructures in a reversible and deterministic way. We demonstrate that electrically formed areas with a nearly single variant alignment can be overwritten with different alignments repeatedly, which reflects the reversible and nonvolatile nature of the switching process. In addition, we explore the functionality of the created nanostructures by clarifying ferroelectric polarizations and observing the improvement of the electronic conduction at the phase boundary. Our findings provide new pathways to one-dimensional rewritable nanostructures and inspire researchers to conceive various multifunctional devices by combining the superb electromechanical property with their unique interfacial electronic conduction properties at nanoscale phase boundaries.

Deep ultraviolet (UV) light-emitting diodes (LEDs) at a wavelength of 226 nm based on AlGaN/ AlN multiple quantum wells using p-type Si as both the hole supplier and the reflective layer are demonstrated. In addition to the description of the hole transport mechanism that allows hole injection from p-type Si into the wide bandgap device, the details of the LED structure which take advantage of the p-type Si layer as a reflective layer to enhance light extraction efficiency (LEE) are elaborated. Fabricated LEDs were characterized both electrically and optically. Owing to the efficient hole injection and enhanced LEE using the p-type Si nanomembranes (NMs), an optical output power of 225 lW was observed at 20 mA continuous current operation (equivalent current density of 15 A/cm 2) without external thermal management. The corresponding external quantum efficiency is 0.2%, higher than any UV LEDs with emission wavelength below 230 nm in the continuous current drive mode. The study demonstrates that adopting p-type Si NMs as both the hole injector and the reflective mirror can enable high-performance UV LEDs with emission wavelengths, output power levels, and efficiencies that were previously inaccessible using conventional p-in structures.

Ultraviolet (UV) light emission at 229 nm wavelength from diode structures based on AlN/Al0.77Ga0.23N quantum wells and using p-type Si to significantly increase hole injection was reported. Both electrical and optical characteristics were measured. Owing to the large concentration of holes from p-Si and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm 2 under continuous wave operation and without external thermal management. An optical output power of 160 µW was obtained with corresponding external quantum efficiency of 0.027%. This study demonstrates that by adopting p-type Si nanomembrane contacts as hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composition AlGaN quantum wells, enabling emission wavelengths and power levels that were previously inaccessible using traditional p-i-n structures with poor hole injection efficiency.Demand for ultraviolet (UV) light emitting diodes (LEDs) is increasing due to broad applications in biological and chemical detections, decontamination, medical treatment, high density optical recording, and lithography 1-6 . The group III-nitride materials system is the most attractive candidate for UV LEDs spanning the UVA, UVB, and UVC 7-15 owing to its wide bandgap range (GaN: 3.3eV -AlN: ~6.2eV). However, as the wavelength gets shorter, the external quantum efficiency (EQE) becomes significantly degraded. Along with challenges in growth of high Al composition AlxGa1-xN material with low defect densities, the doping concentration limitations and high ionization energy of acceptors for wide gap AlGaN render the p-side of the diode structure quite resistive and the resulting hole injection efficiency is poor. In addition, achieving an Ohmic metal contact to typical p-layers with low contact resistance remains a critical limitation to obtaining an electrically efficient DUV LED. The approach used in this work overcomes both limitations.A variety of approaches have been resorted to circumventing the fundamental p-type doping challenges, such as polarization doping 1,5,16,17 and tunnel junctions [18][19][20] . Both methods require careful control of precursor fluxes for grading Al composition over the growth process, which complicates the epitaxy technique. We have reported a 237 nm UV LED using silicon as an efficient hole injector and postulated that shorter wavelength emission would be obtainable

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Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) AlO coated Ga-polar GaN were studied. The UV/O treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the AlO/GaN interfaces. The UV/O treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of AlO deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the AlO/GaN interfaces. An optimal UV/O treatment condition also exists for realizing the "best" interface conditions. The study of UV/O treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.