Novel Devices ♦ news digest


pairing quantum dots with carbon-rich buckyballs. In that study, they found the opposite effect: Buckyballs decreased the dots “on” time while enhancing the transfer of electrons.


In other applications combing dots and polymers, such as LEDs or biosensors, scientists are looking for ways to suppress charge transfer as this process becomes detrimental.


“Knowing these fundamentals and how to control these processes at the nanoscale should help us optimise the use of quantum dots for a wide range of applications,” Cotlet concludes.


More detail of this work has been published in the paper, “Core size dependent hole transfer from a photoexcited CdSe/ZnS quantum dot to a conductive polymer,” by Huidong Zang et al in Chem. Commun., 2014. DOI: 10.1039/C3CC47975G.


This research was funded by the DOE Office of Science and by the Air Force Office of Scientific Research.


III-V transistor offers high- performance at low voltage


Researchers have demonstrated an InGaAs/GaAsSb broken-gap tunnel field effect transistor where the energy barrier was close to zero


A new type of transistor could enable possible fast and low-power computing devices for energy-constrained applications according to Penn State researchers.


Applications where this development could be of use include smart sensor networks, implantable medical electronics and ultra-mobile computing.


Called a near broken-gap tunnel field effect transistor (TFET), the new device uses the quantum mechanical tunnelling of electrons through an ultrathin energy barrier to provide high current at low voltage.


Penn State, the National Institute of Standards and Technology and IQE, a specialty wafer manufacturer, jointly presented their findings at the International Electron Devices Meeting in Washington, D.C. The IEDM meeting includes representatives from all of the major chip companies and is the recognised forum for reporting breakthroughs in semiconductor and electronic technologies.


Tunnel field effect transistors are considered to be a potential replacement for current CMOS transistors, as


A scanning electron microscope top view of the TFET, (Image: Suman Datta/Penn State)


“This transistor has previously been developed in our lab to replace MOSFET transistors for logic applications and to address power issues,” says lead author and Penn State graduate student Bijesh Rajamohanan. “In this work we went a step beyond and showed the capability of operating at high frequency, which is handy for applications where power concerns are critical, such as processing and transmitting information from devices implanted inside the human body.”


For implanted devices, generating too much power and heat can damage the tissue that is being monitored, while draining the battery requires frequent replacement surgery. The researchers, led by Suman Datta, professor of electrical engineering, tuned the material composition of the InGaAs/GaAsSb so that the energy barrier was close to zero - or near broken gap. This allowed electrons to tunnel through the barrier when desired. To improve amplification, the researchers moved all the contacts to the same plane at the top surface of the vertical transistor.


device makers search for a way to continue shrinking the size of transistors and packing more transistors into a given area. The main challenge facing current chip technology is that as size decreases, the power required to operate transistors does not decrease in step.


The results can be seen in batteries that drain faster and increasing heat dissipation that can damage delicate electronic circuits. Various new types of transistor architecture using materials other than standard silicon are being studied to overcome the power consumption challenge.


January / February 2014 www.compoundsemiconductor.net 165


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