Development of AlAsSb as a barrier material for ultra-thin-channel InGaAs nMOSFETs
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Development of AlAsSb as a barrier material for ultra-thin-channel InGaAs nMOSFETs Cheng-Ying Huang1, Jeremy J. M. Law1, Hong Lu2, Mark J. W. Rodwell1, and Arthur C. Gossard1,2 1 Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, U.S.A. 2 Materials Department, University of California, Santa Barbara, CA 93106, U.S.A. ABSTRACT We investigated AlAs0.56Sb0.44 epitaxial layers lattice-matched to InP grown by molecular beam epitaxy (MBE). Silicon (Si) and tellurium (Te) were studied as n-type dopants in AlAs0.56Sb0.44 material. Similar to most Sb-based materials, AlAs0.56Sb0.44 demonstrates a maximum active carrier concentration around low-1018 cm-3 when using Te as a dopant. We propose the use of a heavily Si-doped InAlAs layer embedded in the AlAsSb barrier as a modulation-doped layer. The In0.53Ga0.47As/AlAs0.56Sb0.44 double heterostructures with a 10 nm InGaAs well show an electron mobility of about 9400 cm2/V·s at 295 K and 32000 cm2/V·s at 46 K. A thinner 5 nm InGaAs well has an electron mobility of about 4300 cm2/V·s at 295 K. This study demonstrates that AlAs0.56Sb0.44 is a promising barrier material for highly scaled InGaAs MOSFETs and HEMTs. INTRODUCTION III-V metal-oxide-semiconductor field effect transistors (MOSFETs), particularly InxGa1– (x≥0.53), are being investigated to replace silicon for future CMOS VLSI technology. At the same oxide thickness, the low electron transport mass with resultant high saturated and injection velocity may provide high on-state current and transconductance. To date, most InGaAs MOSFETs are built utilizing the In0.53Ga0.47As/In0.52Al0.48As material system. Aiming at replacing Si channels below 10 nm gate-length generations, the InGaAs channel thickness must be scaled down (tch~2-5 nm) in order to maintain strong electrostatic gate control. Thinning the channel could also decrease the electron wave-function depth, increase total gate capacitance and device transconductance. However, given the small conduction band offset between In0.53Ga0.47As and In0.52Al0.48As (~0.52 eV) [1], upon shrinking the InGaAs channel thickness, the increased eigenstate energy will cause increased electron wave-function penetration into the barrier layer, leading to a parallel conduction path in the barrier. The channel electron spillover into the barrier layer will degrade electron transport velocity and reduce device performance [2]. Additionally, the increasing eigenstate energy with decrease of channel thickness will reduce the total allowable sheet charge density in the channel before the Fermi level reaches the conduction band energy of the barrier layer. Further increases in gate voltage will modulate the parasitic charge in the barrier layer with resultant less confinement and lower transconductance. Therefore, to mitigate these problems, a wider band-gap barrier material with higher conduction band offset to InGaAs channels is needed for realizing InGaAs MOSFETs for sub-10-nm generations. In this work, an AlAs0.56Sb0.44 layer lattice matched to InP is propo
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