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Research Review: Double Barrier Increases MOSFET Mobility

Scientists from the University of Texas at Austin have broken the channel mobility record for an inversion-type/accumulationtype III-V MOSFET.

The key to realizing a mobility of 4729 cm2/Vs was the addition of an InP/In0.52Al0.48As barrier on top of the transistor. This addition reduces the chance of electrons spilling over from the channel to the barrier, where mobility is compromised.

A higher mobility of 5500 cm2/Vs has been reported in an III-V MOSHEMTs-like structure, which has channel electrons provided by a silicon δ-doping layer, rather than a gate bias. However, realizing this higher mobility comes at the expense of fabricating a more complicated structure, according to team-member Jack Lee.

The University of Texas researchers could further increase the channel mobility of their devices by increasing the thickness of their InP layer in the barrier beyond 5 nm.“But we have not tried [this] because the short channel effect would be much more severe," says Lee. “ In our work we used long channel devices [with a length of 20 μm], where short channel effects are not a problem."

The team now plans to work on devices with new channel layers, such as InAs, which promise even higher mobility. “We will also measure effective channel mobility for III-V MOSFETs at different temperatures, and find scattering mechanisms that influence channel mobility," says Lee.

H. Zhao et al. Appl. Phys. Lett. 96 102101 (2010)

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