Suppressing on-chip electromagnetic crosstalk for spin qubit devices J. Appl. Phys. 112, 064315 (2012) Ultra high density three dimensional capacitors based on Si nanowires array grown on a metal layer Appl. Phys. Lett. 101, 083110 (2012) Bipolar and tri-state unipolar resistive switching behaviors in Ag/ZnFe2O4/Pt memory devices Appl. Phys. Lett. 101, 063501 (2012) Optimization of nanotube thermal interconnects for near-field radiative heat transport Appl. Phys. Lett. 101, 063115 (2012) High-temperature gold metallization for ZnO nanowire device on a SiC substrate A metallization scheme has been developed for obtaining low ohmic contacts to n-GaN with a low contact resistance. The metal contact is a Ti/Al/Ti/Au composite with layers that are respectively 30, 100, 30, and 30 nm thick. Contacts with a specific contact resistivity s , as low as 6.0 ϫ10 Ϫ7 ⍀ cm 2 for a doping level of 1.40ϫ10 20 cm Ϫ3 were obtained after annealing the sample for 30 s at 750°C in a rapid thermal annealer. The Ti placed on top of the traditional Ti/Al contact appears to have the advantage of tying up the excess Al; therefore it does not form a mottled contact. Some of the additional Ti-Al intermetallic alloys that are formed also have beneficial effects. The Ti-Au layer forms a robust upper portion of the composite, which enables the contacts to have high-temperature applications.

A series of experiments have been conducted to systematically study the effects of growth conditions (NH3 flow rate, growth temperature, chamber pressure, and growth location) on the size (nano, meso, or micro) and the shape (one, two, or three dimensional) of GaN single crystal products grown by a direct reaction of Ga with NH3. A growth map with a wider range of experimental parameters was developed; it has three distinct zones. The size and shape of the products in every zone were found to depend on both temperature and NH3 flow rate with other growth conditions fixed. An effective surface diffusion length consisting of the Ga atomic surface diffusion length and the GaN molecular surface diffusion length, and the anisotropy of the Ga surface diffusion length and the GaN growth rate in different growth directions were introduced into the growth model, in such a way that it allowed successful explanation of all observed results. The optimal growth parameters could thus be determined, which conclusively demonstrated that nanowires with uniform diameter, clear crystal structure, length larger than 1 mm, uniform location distribution, and high yield can be obtained. Such a growth map based on in-depth understanding of the growth mechanism provides a clear direction for growing various materials with desired size and shape.

A novel two-step surface treatment method has been developed to realize low resistance nonalloyed ohmic contact to n-type GaN doped with Si to 6ϫ10 17 cm Ϫ3 . The removal of native oxide ͑oxides and hydroxides͒ formed on GaN surface is crucial for successful creation of nonalloyed low resistance ohmic contact. In the case of GaN, plasma etching of the material surface prior to metal deposition holds promise for developing such nonalloyed ohmic contacts. In this article, the effects of the postetch chemical treatment of the n-type GaN surface on the Ti based nonalloyed contact performance have been investigated. Contacts on samples without reactive ion etching ͑RIE͒ showed Schottky behavior. However, contacts on samples with 15 s of RIE using Cl 2 showed ohmic behavior. The contact resistivity of this contact reached to s ϭ1.2ϫ10 Ϫ3 ⍀ cm 2 . Treating the RIE etched sample in boiling aqua regia for 5 min yielded a contact resistivity on the order of 3.6 ϫ10 Ϫ4 ⍀ cm 2 . Dramatic improvement in current-voltage characteristics was observed after boiling RIE etched samples in KOH for 5 min. It yielded contact resistivity on the order of s ϳ7 ϫ10 Ϫ5 ⍀ cm 2 , which is comparable to the contact resistivity of alloyed contacts. It was demonstrated, for the first time, that chemical treatment of postetched GaN surfaces employing KOH is very promising for new generation of nonalloyed ohmic contacts. This study suggested that the reduction of contact resistivity results from the effective removal of surface oxides and hydroxides, which act as an impeding barrier for electron transport.

Free-standing InAs nanowires and whiskers were grown employing reaction of indium (In) liquid and vapor with GaAs substrate. The arsenic (As) atoms resulting from this reaction were transported by a flow of N2 or NH3 to the growth location where they reacted with In to produce InAs nanowires and whiskers. Scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy of the products indicate that the diameter of the nanowires and whiskers ranges from 15 nm to 2 μm depending on the growth temperature, the composition is InAs, and the structure is zinc-blende crystal with [110] or [100] growth direction. The As source and growth mechanism were discussed. The method for synthesis involved no any template, catalyst, toxic As source, nor even lattice matched substrate.