Devices – Page 3

Cathodoluminescence lithography

In a brief paper in Applied Physics Letters, a group from the Solid State Physics department at TU Berlin report an interesting process to build isolating mesas to support single quantum dots. Given a random distribution of quantum dots on a surface, one can select specifically those which suit one’s purposes as follows. Coat the sample with PMMA, scan with an electron beam thereby exciting cathodoluminescence from the quantum dots. Return the beam to the selected locations and invert the resist tone. Develop, etch, ash, etc. This leaves the selected quantum dots isolated from one another, each on its own small mesa. Apparently, the dose required to acquire sufficient luminescence signal is enough to fully expose the PMMA (in the positive sense). This is why the polymerization (tone reversal) step is needed.

The paper can also be found on the arXiv.

Gap-free graphene FET

To date, field effect transistors based on graphene have all introduced a band gap into the graphene beneath the gate. Various treatments like oxidation, hydrogenation, etc. are difficult to control and furthermore adversely impact the novel properties of pristine graphene which one would like to retain. In the May 28 issue of PNAS, a joint work between researchers at KAIST and KIAS in Korea and at CalTech in southern California proposes using pristine graphene with a saw-toothed gate field instead of the ordinary rectangular gate field. Since gate geometry is something we know how to engineer, this proposal may lead to more readily manufacturable digital graphene devices.

Single electron CMOS transistor

A group at NIST reports that they have created single electron transistors in a CMOS process. These are meant to support electrometry, thermometry, and quantum information processing. As experimental devices, they are rather large but they do work over temperatures ranging from 30 mK to 300 K. The nanowire and gates at the heart of the devices were formed by e-beam lithography in HSQ and chlorine etch.

Details may be found on the arXiv as arXiv:1206.2872v1.

Boron nitride nanotubes

Marvin Cohen and Alex Zettl have published a small review of boron nitride nanotubes [Physics Today 63 (11), 34-38 (2010)]. Two potential applications loom. The authors point out that these nanotubes (abbreviated BNNT) show field emission that is unusually stable compared to carbon nanotube field emission. Also, BNNT field emission closely follows the Fowler-Nordheim law. The implications to cold field emission device construction are obvious.

Furthermore, the BNNT bandgap can be tuned by application of an electric field transverse to the tube axis. At zero applied voltage, the gap is around 5 eV. At sufficiently large applied voltage, the band gap collapses to 0 eV. Perhaps one may use a BNNT as a transistor channel based on this giant Stark effect.

Other electronic applications may arise from the peculiar spatial localization of the lowest conduction band. It is physically situated in the tube, leading lightly doped BNNTs to act like plumbing for nearly a free electron gas.

III-V compounds on silicon

The Javey group at UC Berkeley has developed a novel method for placing III-V compound structures on silicon substrates. The method appeared in Nature 468, 286-9 (11 November 2010) [doi:10.1038/nature09541].

After growing and patterning thin InAs on a suitable III-V substrate, the patterned elements are picked up by a silicon rubber carrier and transferred to an oxidized silicon wafer, where further processing can take place.

Longer blog postings can be found at IEEE Spectrum , and at Technology Review.