UC Santa Barbara

As device scaling continues to sub-10-nm regime, III-V InGaAs/InAs metal-

oxide-semiconductor field-effect transistors (MOSFETs) are promising candidates

for replacing Si-based MOSFETs for future very-large-scale integration (VLSI)

logic applications. III-V InGaAs materials have low electron effective mass and

high electron velocity, allowing higher on-state current at lower VDD and reducing

the switching power consumption. However, III-V InGaAs materials have a nar-

rower band gap and higher permittivity, leading to large band-to-band tunneling

(BTBT) leakage or gate-induced drain leakage (GIDL) at the drain end of the

channel, and large subthreshold leakage due to worse electrostatic integrity. To

utilize III-V MOSFETs in future logic circuits, III-V MOSFETs must have high

on-state performance over Si MOSFETs as well as very low leakage current and

low standby power consumption. In this dissertation, we will report InGaAs/InAs

ultra-thin-body MOSFETs. Three techniques for reducing the leakage currents in

InGaAs/InAs MOSFETs are reported as described below.

1) Wide band-gap barriers: We developed AlAs0.44Sb0.56 barriers lattice-match

to InP by molecular beam epitaxy (MBE), and studied the electron transport

in In0.53Ga0.47As/AlAs0.44Sb0.56 heterostructures. The InGaAs channel MOS-

FETs using AlAs0.44Sb0.56 bottom barriers or p-doped In0.52Al0.48As barriers

were demonstrated, showing significant suppression on the back barrier leakage.

2) Ultra-thin channels: We investigated the electron transport in InGaAs and

InAs ultra-thin quantum wells and ultra-thin body MOSFETs (tch∼2-4 nm).

For high performance logic, InAs channels enable higher on-state current, while

for low power logic, InGaAs channels allow lower BTBT leakage current.

3) Source/Drain engineering: We developed raised InGaAs and recessed InP

source/drain spacers. The raised InGaAs source/drain spacers improve electro-

statics, reducing subthreshold leakage, and smooth the electric field near drain,

reducing BTBT leakage. With further replacement of raised InGaAs spacers by

recessed, doping-graded InP spacers at high field regions, BTBT leakage can be

reduced ∼100:1.

Using the above-mentioned techniques, record high performance InAs MOS-

FETs with a 2.7 nm InAs channel and a ZrO2 gate dielectric were demonstrated

with Ion = 500 µA/µm at Ioff = 100 nA/µm and VDS =0.5 V, showing the highest

on-state performance among all the III-V MOSFETs and comparable performance

to 22 nm Si FinFETs. Record low leakage InGaAs MOSFETs with recessed InP

source/drain spacers were also demonstrated with minimum Ioff = 60 pA/µm at

30 nm-Lg , and Ion = 150 µA/µm at Ioff = 1 nA/µm and VDS =0.5 V. This re-

cessed InP source/drain spacer technique improves device scalability and enables

III-V MOSFETs for low standby power logic applications. Furthermore, ultra-

thin InAs channel MOSFETs were fabricated on Si substrates, exhibiting high

yield and high transconductance gm ∼2.0 mS/µm at 20 nm-Lg and VDS =0.5 V.

With further scaling of gate lengths, a 12 nm-Lg III-V MOSFET has shown max-

imum Ion/Ioff ratio ∼8.3×10 5 , confirming that III-V MOSFETs are scalable to

sub-10-nm technology nodes.