http://hdl.handle.net/1721.1/3650 http://dspace.mit.edu:80/retrieve/3312 http://hdl.handle.net/1721.1/3650 http://hdl.handle.net/1721.1/35834 ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application Le, Hong Quang Chua, Soo-Jin Fitzgerald, Eugene A. Loh, Kian Ping The ZnO nanorods with the length of 1-1.5 μm were deposited on p-GaN by hydrothermal synthesis at low temperature 100°C. The structural and optical properties of the as-grown ZnO rods were investigated by X-Ray diffraction (XRD) and photoluminescence (PL) spectra. After annealing treatment the as-grown films in air at 600°C, 30min, and the ZnO rods showed good crystallinity and optical properties with strong UV emission at 378 nm. In addition, a sharp UV emission peak at 369.45 nm with the FWHM 20 meV, which attributed to the bound exciton recombination, was also observed from the ZnO rods at 80K. Next, the e-beam evaporation method was used to deposit metal contact on n-ZnO and p-GaN. Here, we use Au and Ni/Au as metal contacts for n-ZnO and p-GaN, respectively. The current-voltage characteristics of the fabricated n-ZnO/p-GaN heterojunction revealed rectifying behavior with a leakage current of 10⁻⁸ A at -10V, a forward current 4x10⁻⁶ A at 10V bias. The heterojunction also showed a good photoresponse, with the change of the current – voltage characteristics under ultraviolet illumination. Under UV illumination, the forward turn on voltage changed to 7.5V. This result showed the ability to manipulate the electron transport in the ZnO based heterojunction devices. Fri, 29 Dec 2006 22:58:59 GMT http://hdl.handle.net/1721.1/35833 Workfunction Tuning of n-Channel MOSFETs Using Interfacial Yttrium Layer in Fully Silicided Nickel Gate Yu, Hongpeng Pey, Kin Leong Choi, Wee Kiong Chi, D.Z. Fitzgerald, Eugene A. Antoniadis, Dimitri A. Continual scaling of the CMOS technology requires thinner gate dielectric to maintain high performance. However, when moving into the sub-45 nm CMOS generation, the traditional poly-Si gate approach cannot effectively reduce the gate thickness further due to the poly-depletion effect. Fully silicided Ni metal gate (FUSI) has been proven to be a promising solution. Ni FUSI metal gate can significantly reduce gate-line sheet resistance, eliminate boron penetration to channels and has good process compatibility with high-k gate dielectric. But Ni FUSI has a mid-gap workfunction which is not suitable for high-performance CMOS applications where the band-edge workfunction is required. In this paper, we propose to tune the nickel (Ni) fully silicided metal gate (FUSI) workfunction via an yttrium/Si/Ni gate stack structure. The workfunction of such structure indicates that the Y interlayer can effectively tune the Ni FUSI workfunction from the mid gap to the conduction band edge of silicon by controlling the interlayer thickness. The gate stack workfunction starts to saturate to the pure yttrium value when the yttrium interlayer is >1.6 nm. This indicates the chemical potential of the material adjacent to gate electrode/gate insulator plays an important role in the determination of the workfunction. Fri, 29 Dec 2006 22:58:59 GMT http://hdl.handle.net/1721.1/35832 Study of Stress Evolution of Germanium Nanocrystals Embedded in Silicon Oxide Matrix Chew, Han Guan Choi, Wee Kiong Chim, Wai Kin Foo, Y.L. Fitzgerald, Eugene A. Germanium (Ge) nanocrystals had been synthesized by annealing co-sputtered SiO₂-Ge in N₂ and/or forming gas (90% N₂ + 10% H₂) at temperatures ranging from 700 to 1000°C from 15 to 60 min. It was concluded that the annealing ambient, temperature and time have a significant influence on the formation and evolution of the nanocrystals. We also showed that a careful selective etching of the annealed samples in hydrofluoric solution enabled the embedded Ge nanocrystals to be liberated from the Si oxide matrix. From the Raman results of the as-grown and the liberated nanocrystals, we established that the nanocrystals generally experienced compressive stress in the oxide matrix and the evolution of these stress states was intimately linked to the distribution, density, size and quality of the Ge nanocrystals. Fri, 29 Dec 2006 22:58:59 GMT http://hdl.handle.net/1721.1/35831 Ordering Control of Self-Assembled Colloidal Crystals Koh, Yaw Koon Chiang, Yet-Ming Wong, Chee Cheong Colloidal crystals are 3D nanostructures formed by self assembly of nanoparticles in suspension. The interaction forces between the colloid particles are expected to affect the ordering and the defect density in the resultant crystal. Based on this insight, the effect of ionic strength on the quality of the colloidal crystal is examined. It is found that at intermediate ionic strength, it is possible to get the best ordering of the colloidal crystal. The reason for this is explained based on previous work on the structural changes in an assembling colloidal crystal. A method for reducing the defect density in colloidal crystal will also be proposed. Fri, 29 Dec 2006 22:58:59 GMT