We present a systematic study of the low-temperature magnetotransport
properties of modulation-doped GaAs heterostructures co examine the de
vice isolation mechanism in a low-energy (150 eV) Ar+ ion exposure pro
cess. Measurements were carried out repeatedly on the same Hall bar as
a function of the ion exposure time. A gradual evolution from paralle
l conduction to strictly single-channel conduction was observed. The c
arrier density of the upper channel was depleted by ion surface millin
g, while the lower channel two-dimensional electron gas was essentiall
y unaffected. The data indicated that carrier depletion and the subseq
uent breakdown in electron screening of the long-range random potentia
l was the main reason for device isolation during the low-energy ion e
xposure process;in agreement with recent theoretical work. (C) 1996 Am
erican Institute of Physics.