news digest ♦ Novel Devices


The reported strained germanium p-channel FinFETs on SiGe trench buffer achieved peak transconductance (gmSAT) values of 1.3mS/µm at VDS of 0.5V with good short channel control down to 60nm gate length. The transconductance to subthreshold slope ratio of the devices (gmSAT/SSSAT) is high compared to published relaxed germanium FinFET devices.


Future developments will focus on improving the device performance through p-doping in the SiGe, optimising silicon cap passivation thickness on the germanium, and improving the gate wrap of the channel.


“Unlike published germanium FinFETs, this work demonstrates a Ge-SiGe heterostructure-based quantum-well device in a FinFET form, which not only provides strain benefits but also- enhancesshort-channel control,” says Nadine Collaert, program manager of the Ge/IIIV device R&D.


“Just recently, we reported the implementation of IIIV material into the device architecture using a fin replacement process,” states Aaron Thean, director of the logic R&D program at imec. “This new achievement, implementing germanium into the channel through our fin replacement process, is another key ingredient to our menu of process possibilities for monolithic heterogeneous integration to extend CMOS and SOCs.”


Imec’s research into next-generation FinFETs is part of its core CMOS program, in cooperation with key partners including Intel, Samsung, TSMC, Globalfoundries, Micron, SK Hynix, Toshiba/Sandisk, Panasonic, Sony, Qualcomm, Altera, Fujitsu, nVidia and Xilinx.


Versatile GaAs-AlGaAs nanowire lasers


III-V nanowires could potentially be used in multiple applications if several problems are overcome. These applications include silicon-on-chip optical interconnects, optical transistors, integrated optoelectronics for telecoms, laser arrays and bbiological and environmental sensing


Thread-like semiconductor structures called nanowires, so thin that they are effectively one-dimensional, show potential as lasers. These lasers could be used for applications in computing, communications, and sensing.


Now, scientists at the Technische Universität München (TUM) have demonstrated laser action in semiconductor nanowires that emit light at technologically useful wavelengths and operate at room temperature.


168 www.compoundsemiconductor.net January / February 2014


Scanning electron micrograph of the as-grown core-shell GaAs-Al0.25Ga0.75As NWs revealing typical lengths ranging from 11 to 16 μm and an areal density of the order of ~108 cm−2


The nanowires’ tailored core-shell structure enables them to act both as lasers, generating coherent pulses of light, and as waveguides, similar to optical fibres. Like conventional communication lasers, these nanowires are made of GaAs-AlGaAs semiconductors, with the right bandgap to emit light in the near-infrared.


A unique advantage, Finley explains, is that the nanowire


They have documented this breakthrough in the journal Nature Communications and in two Nano Letters papers, where they have disclosed further results showing enhanced optical and electronic performance.


“Nanowire lasers could represent the next step in the development of smaller, faster, more energy-efficient sources of light,” says Jonathan Finley, director of TUM’s Walter Schottky Institute.


Potential applications include on-chip optical interconnects or even optical transistors to speed up computers, integrated optoelectronics for fibre-optic communications, and laser arrays with steerable beams.


“But nanowires are also a bit special,” Finley adds, “in that they are very sensitive to their surroundings, have a large surface-to-volume ratio, and are small enough, for example, to poke into a biological cell.” Thus nanowire lasers could also prove useful in environmental and biological sensing.


These experimental nanowire lasers emit light in the near-infrared, approaching the “sweet spot” for fibre-optic communications. They can be grown directly on silicon, presenting opportunities for integrated photonics and optoelectronics. And they operate at room temperature, a prerequisite for real-world applications.


Tailored in the lab, with an eye toward industry


Tiny as they are - a hundred to a thousand times thinner than a human hair - the nanowire lasers demonstrated at TUM have a complex “core-shell” cross-section with a profile of differing semiconductor materials tailored virtually atom by atom.


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