We demonstrate the realization of the high-brightness and high-efficiency light emitting diodes (LEDs) using dislocation-free indium gallium nitride (InGaN)/gallium nitride (GaN) multiquantum-well (MQW) nanorod (NR) arrays by metal organic-hydride vapor phase epitaxy (MO−HVPE). MQW NR arrays (NRAs) on sapphire substrate are buried in spin-on glass (SOG) to isolating individual NRs and to bring p-type NRs in contact with p-type electrodes. The MQW NRA LEDs have similar electrical characteristics to conventional broad area (BA) LEDs. However, due to the lack of dislocations and the large surface areas provided by the sidewalls of NRs, both internal and extraction efficiencies are significantly enhanced. At 20 mA dc current, the MQW NRA LEDs emit about 4.3 times more light than the conventional BA LEDs, even though overall active volume of the MQW NRA LEDs is much smaller than conventional LEDs. Moreover, the fabrication processes involved in producing MQW NRA LEDs are almost the same for conventional BA LEDs. It is, thus, not surprising that the total yield of these MQW NRA LEDs is essentially the same as that of conventional BA LEDs. The present method of utilizing dislocation-free MQW NRA LEDs is applicable to super-bright white LEDs as well as other semiconductor LEDs for improving total external efficiency and brightness of LEDs.

The demand for non-volatile memory technologies that offer high speed, high storage density and low power consumption has stimulated extensive research into new functional materials and device physics. [1][2][3][4][5] Nano-ferronic devices based on multiferroic/ferroelectric materials have been emerging as nextgeneration nano-electronics, which deal with the interplay between ferroic orders (e.g. ferroelectricity and ferromagnetism) and electronic transport on the nanoscale. [ 6 ] Recent investigations into various multiferroic/ferroelectric materials have revealed remarkable polarization dependent electronic transport properties, which include signifi cant electroresistance effects in a switchable ferroelectric diode [7][8][9][10][11] and multiferroic/ferroelectric tunnel junctions (M/FTJs) [12][13][14][15][16][17] and intriguing charge conduction in ferroelectric domain/walls. [ 18 , 19 ] These conduction properties can be utilized for fast and non-destructive readout in emergent non-volatile memories such as resistive random access memory (RRAM) and memristor. [ 20 ] Especially, ferroelectric-resistive memories based on ferroelectric diode and tunnel junctions have demonstrated that it is possible to achieve high resistive ON/OFF ratio, high speed and low write power with a high reproducibility by controlling ferroelectric polarization. In a switchable ferroelectric diode, the Schottky-to-Ohmic contacts, forming at the interfaces between metal electrodes and semiconducting ferroelectric thin fi lms, are reversibly modulated by the polarization fl ipping which gives rise to rectifi cation direction switching . [8][9][10][11] The tunnel junctions with ultrathin ferroelectric barrier yield a giant tunnel electroresistance effect resulting from the change of asymmetric tunnel barrier heights controlled by ferroelectric polarization direction. However, multiferroic/ferroelectric nano-structures such as nano-islands and nano-wires have not yet been exploited for ferroelectric-resistive memories, although large storage capacity, lower power consumption and high reliability are expected for such nano-structures. They also provide an effective way to understand and manipulate the ferroelectric-resistive switching, piezoelectricity, polarization and domain structures on the nanoscale. On the other hand, the fabrication of ferroelectric nano-structures through bottom-up approach is crucial to realizing high-performance of nano-ferronic devices since top-down approach may induce serious deterioration in ferroelectric nano-structures. [ 21 , 22 ] Here, we explored the local charge conductions and their coupling with ferroelectric polarization in highly oriented ferroelectric BiFeO 3 (BFO) nano-islands array by using conductive atomic force microscopy (CAFM) and piezoresponse force microscopy (PFM). We observed a switchable diode effect in BFO nano-islands grown on SrRuO 3 /SrTiO 3 (SRO/STO) substrate, which showed the direct correlation between rectifi cation and ferroelectric polarization directions. The rectifi cation...

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