The fabrication of highly functional materials for practical devices requires a deep understanding of the association between morphological and structural properties and applications. A controlled hydrothermal method to produce single crystal ZnO hexagonal nanodisks, nanorings, and nanoroses using a mixed solution of zinc sulfate (ZnSO4) and hexamethylenetetramine (HMTA) without the need of catalysts, substrates, or templates at low temperature (75 °C) is introduced. Metal-semiconductor-metal (MSM) ultraviolet (UV) detectors were fabricated based on individual and multiple single-crystal zinc oxide (ZnO) hexagonal nanodisks. High quality single crystal individual nanodisk devices were fabricated with inkjet-printed silver electrodes. The detectors fabricated show record photoresponsivity (3300 A/W) and external quantum efficiency (1.2 × 10(4)), which we attribute to the absence of grain boundaries in the single crystal ZnO nanodisk and the polarity of its exposed surface.
Enhanced gas sensing properties of ZnO were achieved by designing hierarchical nanostructures with high surface-to-volume ratios and more exposed polar facets.
The size of a metal oxide nanostructure plays a key role in its performance as a gas sensor.
A differential Hall effect technique has been developed to obtain doping profiles at a depth resolution down to 2 nm with junction depths of about 20 nm. We have determined the electrical characteristics of 5 ϫ 10 14 Sb + cm −2 implanted in (100) silicon at an energy of 5 keV. A comparison was made between carrier concentration profiles and secondary ion mass spectroscopy measurements of the atomic profiles as a function of annealing temperature. We have profiled single energy implants of antimony and also double implants; the latter enables complete profiles to be measured down to the background level of about 10 18 Future generations of (CMOS) devices will require the production of ultrashallow junctions ͑10-20 nm͒ for the source/drain extension regions, 1 but low energy implantation to obtain these layers faces many difficulties. 2 The electrical characteristics, including profiles, of shallow layers have been measured by spreading resistance but there has been little if any study using differential Hall effect measurements. 3,4 However, there are difficulties with profiling such shallow layers using the differential Hall effect technique. For example, the anodization process that has been commonly used in the past 5 does not work well for very thin layers. Also the junction formed as a result of the implantation has a depletion region associated with it which limits the extent of the profile which can be measured. We have considered these problems and have developed a method for determining the electrical profiles by using double implants of antimony and an improved method for removing thin layers ͑1-2 nm͒ uniformly and reproducibly so that the differential Hall technique can be utilised.P-type (100) Si wafers of resistivity of 2 -10 ⍀ cm were implanted at room temperature with 5 ϫ 10 14 Sb + cm −2 at 5 keV. To facilitate the measurement of the carrier profile, a second implant of 3 ϫ 10 13 Sb + at 70 keV was performed into part of the wafer. This produces an antimony concentration of 10 18 -10 19 cm −3 in the tail of the 5 keV implant and moves the n + / p junction deep ͑Ϸ80 nm͒ into the material. All the implants were performed using a 200 kV Danfysik 1090 accelerator. The wafers were annealed at temperatures of 600-1100°C for 10 s in a flowing nitrogen ambient. Electrical measurements were performed on cloverleaf samples using an Accent HL5900 Hall system with In/ Ga eutectic used for ohmic contact formation.For differential Hall effect profiling, we have developed a native oxide growth and strip process, since the conventional anodization technique 5 does not give the necessary reproducibility and control at the nanometer level. The process is to immerse the sample into de-ionized water for 10 s, which enables the growth of a very thin oxide. The sample is then washed and dried before measurement of the sheet Hall coefficient and sheet resistance with the oxide in place. Subsequently, the oxide is removed in 5% buffered hydrofluoric acid and the process of oxidation and measurement repeated until the en...
Antimony implants at 40 keV and at a dose of 4 × 10 14 cm −2 have been characterized for their potential use in n-type shallow junction formation. The electrical characterization was done using sheet resistivity and Hall effect measurements. High electrical activities (>80%) and low sheet resistance values (<200 / ) were obtained for annealing temperatures below 800 • C. A novel differential Hall effect technique was used to obtain doping profiles at a depth resolution down to 1 nm, with a comparison made between these and Rutherford backscattering (RBS) measurements of the atomic profile as a function of annealing temperature. The antimony shows insignificant diffusion for annealing temperatures of 800 • C and below, with junction depths of about 60 nm. Electrical activation correlates well with the substitutional fraction of antimony determined by RBS.
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